greater than (>) less than (<)
H 0 always has a symbol with an equal in it. H a never has a symbol with an equal in it. The choice of symbol depends on the wording of the hypothesis test. However, be aware that many researchers (including one of the co-authors in research work) use = in the null hypothesis, even with > or < as the symbol in the alternative hypothesis. This practice is acceptable because we only make the decision to reject or not reject the null hypothesis.
H 0 : No more than 30% of the registered voters in Santa Clara County voted in the primary election. p ≤ 30
H a : More than 30% of the registered voters in Santa Clara County voted in the primary election. p > 30
A medical trial is conducted to test whether or not a new medicine reduces cholesterol by 25%. State the null and alternative hypotheses.
H 0 : The drug reduces cholesterol by 25%. p = 0.25
H a : The drug does not reduce cholesterol by 25%. p ≠ 0.25
We want to test whether the mean GPA of students in American colleges is different from 2.0 (out of 4.0). The null and alternative hypotheses are:
H 0 : μ = 2.0
H a : μ ≠ 2.0
We want to test whether the mean height of eighth graders is 66 inches. State the null and alternative hypotheses. Fill in the correct symbol (=, ≠, ≥, <, ≤, >) for the null and alternative hypotheses. H 0 : μ __ 66 H a : μ __ 66
We want to test if college students take less than five years to graduate from college, on the average. The null and alternative hypotheses are:
H 0 : μ ≥ 5
H a : μ < 5
We want to test if it takes fewer than 45 minutes to teach a lesson plan. State the null and alternative hypotheses. Fill in the correct symbol ( =, ≠, ≥, <, ≤, >) for the null and alternative hypotheses. H 0 : μ __ 45 H a : μ __ 45
In an issue of U.S. News and World Report , an article on school standards stated that about half of all students in France, Germany, and Israel take advanced placement exams and a third pass. The same article stated that 6.6% of U.S. students take advanced placement exams and 4.4% pass. Test if the percentage of U.S. students who take advanced placement exams is more than 6.6%. State the null and alternative hypotheses.
H 0 : p ≤ 0.066
H a : p > 0.066
On a state driver’s test, about 40% pass the test on the first try. We want to test if more than 40% pass on the first try. Fill in the correct symbol (=, ≠, ≥, <, ≤, >) for the null and alternative hypotheses. H 0 : p __ 0.40 H a : p __ 0.40
In a hypothesis test , sample data is evaluated in order to arrive at a decision about some type of claim. If certain conditions about the sample are satisfied, then the claim can be evaluated for a population. In a hypothesis test, we: Evaluate the null hypothesis , typically denoted with H 0 . The null is not rejected unless the hypothesis test shows otherwise. The null statement must always contain some form of equality (=, ≤ or ≥) Always write the alternative hypothesis , typically denoted with H a or H 1 , using less than, greater than, or not equals symbols, i.e., (≠, >, or <). If we reject the null hypothesis, then we can assume there is enough evidence to support the alternative hypothesis. Never state that a claim is proven true or false. Keep in mind the underlying fact that hypothesis testing is based on probability laws; therefore, we can talk only in terms of non-absolute certainties.
H 0 and H a are contradictory.
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Lesson 10 of 24 By Avijeet Biswal
In today’s data-driven world, decisions are based on data all the time. Hypothesis plays a crucial role in that process, whether it may be making business decisions, in the health sector, academia, or in quality improvement. Without hypothesis and hypothesis tests, you risk drawing the wrong conclusions and making bad decisions. In this tutorial, you will look at Hypothesis Testing in Statistics.
Hypothesis Testing is a type of statistical analysis in which you put your assumptions about a population parameter to the test. It is used to estimate the relationship between 2 statistical variables.
Let's discuss few examples of statistical hypothesis from real-life -
Now that you know about hypothesis testing, look at the two types of hypothesis testing in statistics.
Here is what makes hypothesis testing so important in data analysis and why it is key to making better decisions:
One of the biggest benefits of hypothesis testing is that it helps you avoid jumping to the wrong conclusions. For instance, a Type I error could occur if a company launches a new product thinking it will be a hit, only to find out later that the data misled them. A Type II error might happen when a company overlooks a potentially successful product because their testing wasn’t thorough enough. By setting up the right significance level and carefully calculating the p-value, hypothesis testing minimizes the chances of these errors, leading to more accurate results.
Hypothesis testing is key to making smarter, evidence-based decisions. Let’s say a city planner wants to determine if building a new park will increase community engagement. By testing the hypothesis using data from similar projects, they can make an informed choice. Similarly, a teacher might use hypothesis testing to see if a new teaching method actually improves student performance. It’s about taking the guesswork out of decisions and relying on solid evidence instead.
In business, hypothesis testing is invaluable for testing new ideas and strategies before fully committing to them. For example, an e-commerce company might want to test whether offering free shipping increases sales. By using hypothesis testing, they can compare sales data from customers who received free shipping offers and those who didn’t. This allows them to base their business decisions on data, not hunches, reducing the risk of costly mistakes.
Z = ( x̅ – μ0 ) / (σ /√n)
An analyst performs hypothesis testing on a statistical sample to present evidence of the plausibility of the null hypothesis. Measurements and analyses are conducted on a random sample of the population to test a theory. Analysts use a random population sample to test two hypotheses: the null and alternative hypotheses.
The null hypothesis is typically an equality hypothesis between population parameters; for example, a null hypothesis may claim that the population means return equals zero. The alternate hypothesis is essentially the inverse of the null hypothesis (e.g., the population means the return is not equal to zero). As a result, they are mutually exclusive, and only one can be correct. One of the two possibilities, however, will always be correct.
The Null Hypothesis is the assumption that the event will not occur. A null hypothesis has no bearing on the study's outcome unless it is rejected.
H0 is the symbol for it, and it is pronounced H-naught.
The Alternate Hypothesis is the logical opposite of the null hypothesis. The acceptance of the alternative hypothesis follows the rejection of the null hypothesis. H1 is the symbol for it.
Let's understand this with an example.
A sanitizer manufacturer claims that its product kills 95 percent of germs on average.
To put this company's claim to the test, create a null and alternate hypothesis.
H0 (Null Hypothesis): Average = 95%.
Alternative Hypothesis (H1): The average is less than 95%.
Another straightforward example to understand this concept is determining whether or not a coin is fair and balanced. The null hypothesis states that the probability of a show of heads is equal to the likelihood of a show of tails. In contrast, the alternate theory states that the probability of a show of heads and tails would be very different.
Let's consider a hypothesis test for the average height of women in the United States. Suppose our null hypothesis is that the average height is 5'4". We gather a sample of 100 women and determine their average height is 5'5". The standard deviation of population is 2.
To calculate the z-score, we would use the following formula:
z = ( x̅ – μ0 ) / (σ /√n)
z = (5'5" - 5'4") / (2" / √100)
z = 0.5 / (0.045)
We will reject the null hypothesis as the z-score of 11.11 is very large and conclude that there is evidence to suggest that the average height of women in the US is greater than 5'4".
Hypothesis testing is a statistical method to determine if there is enough evidence in a sample of data to infer that a certain condition is true for the entire population. Here’s a breakdown of the typical steps involved in hypothesis testing:
The significance level, often denoted by alpha (α), is the probability of rejecting the null hypothesis when it is true. Common choices for α are 0.05 (5%), 0.01 (1%), and 0.10 (10%).
Choose a statistical test based on the type of data and the hypothesis. Common tests include t-tests, chi-square tests, ANOVA, and regression analysis. The selection depends on data type, distribution, sample size, and whether the hypothesis is one-tailed or two-tailed.
Gather the data that will be analyzed in the test. To infer conclusions accurately, this data should be representative of the population.
Based on the collected data and the chosen test, calculate a test statistic that reflects how much the observed data deviates from the null hypothesis.
The p-value is the probability of observing test results at least as extreme as the results observed, assuming the null hypothesis is correct. It helps determine the strength of the evidence against the null hypothesis.
Compare the p-value to the chosen significance level:
Present the findings from the hypothesis test, including the test statistic, p-value, and the conclusion about the hypotheses.
Depending on the results and the study design, further analysis may be needed to explore the data more deeply or to address multiple comparisons if several hypotheses were tested simultaneously.
To determine whether a discovery or relationship is statistically significant, hypothesis testing uses a z-test. It usually checks to see if two means are the same (the null hypothesis). Only when the population standard deviation is known and the sample size is 30 data points or more, can a z-test be applied.
A statistical test called a t-test is employed to compare the means of two groups. To determine whether two groups differ or if a procedure or treatment affects the population of interest, it is frequently used in hypothesis testing.
You utilize a Chi-square test for hypothesis testing concerning whether your data is as predicted. To determine if the expected and observed results are well-fitted, the Chi-square test analyzes the differences between categorical variables from a random sample. The test's fundamental premise is that the observed values in your data should be compared to the predicted values that would be present if the null hypothesis were true.
ANOVA , or Analysis of Variance, is a statistical method used to compare the means of three or more groups. It’s particularly useful when you want to see if there are significant differences between multiple groups. For instance, in business, a company might use ANOVA to analyze whether three different stores are performing differently in terms of sales. It’s also widely used in fields like medical research and social sciences, where comparing group differences can provide valuable insights.
Both confidence intervals and hypothesis tests are inferential techniques that depend on approximating the sample distribution. Data from a sample is used to estimate a population parameter using confidence intervals. Data from a sample is used in hypothesis testing to examine a given hypothesis. We must have a postulated parameter to conduct hypothesis testing.
Bootstrap distributions and randomization distributions are created using comparable simulation techniques. The observed sample statistic is the focal point of a bootstrap distribution, whereas the null hypothesis value is the focal point of a randomization distribution.
A variety of feasible population parameter estimates are included in confidence ranges. In this lesson, we created just two-tailed confidence intervals. There is a direct connection between these two-tail confidence intervals and these two-tail hypothesis tests. The results of a two-tailed hypothesis test and two-tailed confidence intervals typically provide the same results. In other words, a hypothesis test at the 0.05 level will virtually always fail to reject the null hypothesis if the 95% confidence interval contains the predicted value. A hypothesis test at the 0.05 level will nearly certainly reject the null hypothesis if the 95% confidence interval does not include the hypothesized parameter.
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Depending on the population distribution, you can classify the statistical hypothesis into two types.
Simple Hypothesis: A simple hypothesis specifies an exact value for the parameter.
Composite Hypothesis: A composite hypothesis specifies a range of values.
A company is claiming that their average sales for this quarter are 1000 units. This is an example of a simple hypothesis.
Suppose the company claims that the sales are in the range of 900 to 1000 units. Then this is a case of a composite hypothesis.
The One-Tailed test, also called a directional test, considers a critical region of data that would result in the null hypothesis being rejected if the test sample falls into it, inevitably meaning the acceptance of the alternate hypothesis.
In a one-tailed test, the critical distribution area is one-sided, meaning the test sample is either greater or lesser than a specific value.
In two tails, the test sample is checked to be greater or less than a range of values in a Two-Tailed test, implying that the critical distribution area is two-sided.
If the sample falls within this range, the alternate hypothesis will be accepted, and the null hypothesis will be rejected.
If the larger than (>) sign appears in your hypothesis statement, you are using a right-tailed test, also known as an upper test. Or, to put it another way, the disparity is to the right. For instance, you can contrast the battery life before and after a change in production. Your hypothesis statements can be the following if you want to know if the battery life is longer than the original (let's say 90 hours):
The crucial point in this situation is that the alternate hypothesis (H1), not the null hypothesis, decides whether you get a right-tailed test.
Alternative hypotheses that assert the true value of a parameter is lower than the null hypothesis are tested with a left-tailed test; they are indicated by the asterisk "<".
Suppose H0: mean = 50 and H1: mean not equal to 50
According to the H1, the mean can be greater than or less than 50. This is an example of a Two-tailed test.
In a similar manner, if H0: mean >=50, then H1: mean <50
Here the mean is less than 50. It is called a One-tailed test.
A hypothesis test can result in two types of errors.
Type 1 Error: A Type-I error occurs when sample results reject the null hypothesis despite being true.
Type 2 Error: A Type-II error occurs when the null hypothesis is not rejected when it is false, unlike a Type-I error.
Suppose a teacher evaluates the examination paper to decide whether a student passes or fails.
H0: Student has passed
H1: Student has failed
Type I error will be the teacher failing the student [rejects H0] although the student scored the passing marks [H0 was true].
Type II error will be the case where the teacher passes the student [do not reject H0] although the student did not score the passing marks [H1 is true].
Here are the practice problems on hypothesis testing that will help you understand how to apply these concepts in real-world scenarios:
A telecom service provider claims that customers spend an average of ₹400 per month, with a standard deviation of ₹25. However, a random sample of 50 customer bills shows a mean of ₹250 and a standard deviation of ₹15. Does this sample data support the service provider’s claim?
Solution: Let’s break this down:
1. Calculate the z-value:
z=250-40025/50 −42.42
2. Compare with critical z-values: For a 5% significance level, critical z-values are -1.96 and +1.96. Since -42.42 is far outside this range, we reject the null hypothesis. The sample data suggests that the average amount spent is significantly different from ₹400.
Out of 850 customers, 400 made online grocery purchases. Can we conclude that more than 50% of customers are moving towards online grocery shopping?
Solution: Here’s how to approach it:
z=p-PP(1-P)/n
z=0.47-0.500.50.5/850 −1.74
2. Compare with the critical z-value: For a 5% significance level (one-tailed test), the critical z-value is -1.645. Since -1.74 is less than -1.645, we reject the null hypothesis. This means the data does not support the idea that most customers are moving towards online grocery shopping.
In a study of code quality, Team A has 250 errors in 1000 lines of code, and Team B has 300 errors in 800 lines of code. Can we say Team B performs worse than Team A?
Solution: Let’s analyze it:
p=nApA+nBpBnA+nB
p=10000.25+8000.3751000+800 ≈ 0.305
z=pA−pBp(1-p)(1nA+1nB)
z=0.25−0.3750.305(1-0.305) (11000+1800) ≈ −5.72
2. Compare with the critical z-value: For a 5% significance level (one-tailed test), the critical z-value is +1.645. Since -5.72 is far less than +1.645, we reject the null hypothesis. The data indicates that Team B’s performance is significantly worse than Team A’s.
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Apart from the practical problems, let's look at the real-world applications of hypothesis testing across various fields:
In medicine, hypothesis testing plays a pivotal role in assessing the success of new treatments. For example, researchers may want to find out if a new exercise regimen improves heart health. By comparing data from patients who followed the program to those who didn’t, they can determine if the exercise significantly improves health outcomes. Such rigorous testing allows medical professionals to rely on proven methods rather than assumptions.
In manufacturing, ensuring product quality is vital, and hypothesis testing helps maintain those standards. Suppose a beverage company introduces a new bottling process and wants to verify if it reduces contamination. By analyzing samples from the new and old processes, hypothesis testing can reveal whether the new method reduces the risk of contamination. This allows manufacturers to implement improvements that enhance product safety and quality confidently.
In education and learning, hypothesis testing is a tool to evaluate the impact of innovative teaching techniques. Imagine a situation where teachers introduce project-based learning to boost critical thinking skills. By comparing the performance of students who engaged in project-based learning with those in traditional settings, educators can test their hypothesis. The results can help educators make informed choices about adopting new teaching strategies.
Hypothesis testing is essential in environmental science for evaluating the effectiveness of conservation measures. For example, scientists might explore whether a new water management strategy improves river health. By collecting and comparing data on water quality before and after the implementation of the strategy, they can determine whether the intervention leads to positive changes. Such findings are crucial for guiding environmental decisions that have long-term impacts.
In marketing, businesses use hypothesis testing to refine their approaches. For instance, a clothing brand might test if offering limited-time discounts increases customer loyalty. By running campaigns with and without the discount and analyzing the outcomes, they can assess if the strategy boosts customer retention. Data-driven insights from hypothesis testing enable companies to design marketing strategies that resonate with their audience and drive growth.
Hypothesis testing has some limitations that researchers should be aware of:
After reading this tutorial, you would have a much better understanding of hypothesis testing, one of the most important concepts in the field of Data Science . The majority of hypotheses are based on speculation about observed behavior, natural phenomena, or established theories.
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Hypothesis testing is a statistical method used to determine if there is enough evidence in a sample data to draw conclusions about a population. It involves formulating two competing hypotheses, the null hypothesis (H0) and the alternative hypothesis (Ha), and then collecting data to assess the evidence. An example: testing if a new drug improves patient recovery (Ha) compared to the standard treatment (H0) based on collected patient data.
In statistics, H0 and H1 represent the null and alternative hypotheses. The null hypothesis, H0, is the default assumption that no effect or difference exists between groups or conditions. The alternative hypothesis, H1, is the competing claim suggesting an effect or a difference. Statistical tests determine whether to reject the null hypothesis in favor of the alternative hypothesis based on the data.
A simple hypothesis is a specific statement predicting a single relationship between two variables. It posits a direct and uncomplicated outcome. For example, a simple hypothesis might state, "Increased sunlight exposure increases the growth rate of sunflowers." Here, the hypothesis suggests a direct relationship between the amount of sunlight (independent variable) and the growth rate of sunflowers (dependent variable), with no additional variables considered.
The three major types of hypotheses are:
Several software tools offering distinct features can help with hypothesis testing. R and RStudio are popular for their advanced statistical capabilities. The Python ecosystem, including libraries like SciPy and Statsmodels, also supports hypothesis testing. SAS and SPSS are well-established tools for comprehensive statistical analysis. For basic testing, Excel offers simple built-in functions.
Interpreting hypothesis test results involves comparing the p-value to the significance level (alpha). If the p-value is less than or equal to alpha, you can reject the null hypothesis, indicating statistical significance. This suggests that the observed effect is unlikely to have occurred by chance, validating your analysis findings.
Sample size is crucial in hypothesis testing as it affects the test’s power. A larger sample size increases the likelihood of detecting a true effect, reducing the risk of Type II errors. Conversely, a small sample may lack the statistical power needed to identify differences, potentially leading to inaccurate conclusions.
Yes, hypothesis testing can be applied to non-numerical data through non-parametric tests. These tests are ideal when data doesn't meet parametric assumptions or when dealing with categorical data. Non-parametric tests, like the Chi-square or Mann-Whitney U test, provide robust methods for analyzing non-numerical data and drawing meaningful conclusions.
Selecting the right hypothesis test depends on several factors: the objective of your analysis, the type of data (numerical or categorical), and the sample size. Consider whether you're comparing means, proportions, or associations, and whether your data follows a normal distribution. The correct choice ensures accurate results tailored to your research question.
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Stats Hypothesis testing
Hypothesis testing is one of the most widely used approaches of statistical inference.
The idea of hypothesis testing (more formally: null hypothesis significance testing - NHST) is the following: if we have some data observed, and we have a statistical model, we can use this statistical model to specify a fixed hypothesis about how the data did arise. For the example with the plants and music, this hypothesis could be: music has no influence on plants, all differences we see are due to random variation between individuals.
Such a scenario is called the null hypothesis H0. Although it is very typical to use the assumption of no effect as null-hypothesis, note that it is really your choice, and you could use anything as null hypothesis, also the assumption: “classical music doubles the growth of plants”. The fact that it’s the analyst’s choice what to fix as null hypothesis is part of the reason why there are are a large number of tests available. We will see a few of them in the following chapter about important hypothesis tests.
The hypothesis that H0 is wrong, or !H0, is usually called the alternative hypothesis, H1
Given a statistical model, a “normal” or “simple” null hypothesis specifies a single value for the parameter of interest as the “base expectation”. A composite null hypothesis specifies a range of values for the parameter.
If we have a null hypothesis, we calculate the probability that we would see the observed data or data more extreme under this scenario. This is called a hypothesis tests, and we call the probability the p-value. If the p-value falls under a certain level (the significance level $\alpha$) we say the null hypothesis was rejected, and there is significant support for the alternative hypothesis. The level of $\alpha$ is a convention, in ecology we chose typically 0.05, so if a p-value falls below 0.05, we can reject the null hypothesis.
Test Statistic
Significance level, Power
A problem with hypothesis tests and p-values is that their results are notoriously misinterpreted. The p-value is NOT the probability that the null hypothesis is true, or the probability that the alternative hypothesis is false, although many authors have made the mistake of interpreting it like that \citep[][]{Cohen-earthisround-1994}. Rather, the idea of p-values is to control the rate of false positives (Type I error). When doing hypothesis tests on random data, with an $\alpha$ level of 0.05, one will get exactly 5\% false positives. Not more and not less.
Recall statistical tests, or more formally, null-hypothesis significance testing (NHST) is one of several ways in which you can approach data. The idea is that you define a null-hypothesis, and then you look a the probability that the data would occur under the assumption that the null hypothesis is true.
Now, there can be many null hypothesis, so you need many tests. The most widely used tests are given here.
The t -test can be used to test whether one sample is different from a reference value (e.g. 0: one-sample t -test), whether two samples are different (two-sample t -test) or whether two paired samples are different (paired t -test).
The t -test assumes that the data are normally distributed. It can handle samples with same or different variances, but needs to be “told” so.
The one-sample t-test compares the MEAN score of a sample to a known value, usually the population MEAN (the average for the outcome of some population of interest).
Our null hypothesis is that the mean of the sample is not less than 2.5 (real example: weight data of 200 lizards collected for a research, we want to compare it with the known average weights available in the scientific literature)
One-sample Wilcoxon signed rank test is a non-parametric alternative method of one-sample t-test, which is used to test whether the location (MEDIAN) of the measurement is equal to a specified value
Create fake data log-normally distributed and verify data distribution
Our null hypothesis is that the median of x is not different from 1
Parametric method for examining the difference in MEANS between two independent populations. The t -test should be preceeded by a graphical depiction of the data in order to check for normality within groups and for evidence of heteroscedasticity (= differences in variance), like so:
Reshape the data:
Now plot them as points (not box-n-whiskers):
The points to the right scatter similar to those on the left, although a bit more asymmetrically. Although we know that they are from a log-normal distribution (right), they don’t look problematic.
If data are not normally distributed, we sometimes succeed making data normal by using transformations, such as square-root, log, or alike (see section on transformations).
While t -tests on transformed data now actually test for differences between these transformed data, that is typically fine. Think of the pH-value, which is only a log-transform of the proton concentration. Do we care whether two treatments are different in pH or in proton concentrations? If so, then we need to choose the right data set. Most likely, we don’t and only choose the log-transform because the data are actually lognormally distributed, not normally.
A non-parametric alternative is the Mann-Whitney-U-test, or, the ANOVA-equivalent, the Kruskal-Wallis test. Both are available in R and explained later, but instead we recommend the following:
Use rank-transformations, which replaces the values by their rank (i.e. the lowest value receives a 1, the second lowest a 2 and so forth). A t -test of rank-transformed data is not the same as the Mann-Whitney-U-test, but it is more sensitive and hence preferable (Ruxton 2006) or at least equivalent (Zimmerman 2012).
To use the rank, we need to employ the “formula”-invokation of t.test! In this case, results are the same, indicating that our hunch about acceptable skew and scatter was correct.
(Note that the original t -test is a test for differences between means, while the rank- t -test becomes a test for general differences in values between the two groups, not specifically of the mean.)
Cars example:
Test the difference in car consumption depending on the transmission type. Check wherever the 2 ‘independent populations’ are normally distributed
Graphic representation
We have two ~normally distributed populations. In order to test for differences in means, we applied a t-test for independent samples.
Any time we work with the t-test, we have to verify whether the variance is equal betwenn the 2 populations or not, then we fit the t-test accordingly. Our Ho or null hypothesis is that the consumption is the same irrespective to transmission. We assume non-equal variances
From the output: please note that CIs are the confidence intervales for differences in means
Same results if you run the following (meaning that the other commands were all by default)
The alternative could be one-sided (greater, lesser) as we discussed earlier for one-sample t-tests
If we assume equal variance, we run the following
Ways to check for equal / not equal variance
1) To examine the boxplot visually
2) To compute the actual variance
There is 2/3 times difference in variance.
3) Levene’s test
We change the response variable to hp (Gross horsepower)
The ‘population’ of cars with manual transmission has a hp not normally distributed, so we have to use a test for independent samples - non-parametric
We want to test a difference in hp depending on the transmission Using a non-parametric test, we test for differences in MEDIANS between 2 independent populations
Our null hypothesis will be that the medians are equal (two-sided)
This is a non-parametric method appropriate for examining the median difference in 2 populations observations that are paired or dependent one of the other.
This is a dataset about some water measurements taken at different levels of a river: ‘up’ and ‘down’ are water quality measurements of the same river taken before and after a water treatment filter, respectively
The line you see in the plot corresponds to x=y, that is, the same water measuremets before and after the water treatment (it seems to be true in 2 rivers only, 5 and 15)
Our null hypothesis is that the median before and after the treatment are not different
the assumption of normality is certainly not met for the measurements after the treatment
This parametric method examinates the difference in means for two populations that are paired or dependent one of the other
This is a dataset about the density of a fish prey species (fish/km2) in 121 lakes before and after removing a non-native predator
changing the order of variables, we have a change in the sign of the t-test estimated mean of differences
low p ->reject Ho, means are equal
The normal distribution is the most important and most widely used distribution in statistics. We can say that a distribution is normally distributed when: 1) is symmetric around their mean. 2) the mean, median, and mode of a normal distribution are equal. 3) the area under the normal curve is equal to 1.0. 4) distributions are denser in the center and less dense in the tails. 5) distributions are defined by two parameters, the mean and the standard deviation (sd). 6) 68% of the area of a normal distribution is within one standard deviation of the mean. 7) Approximately 95% of the area of a normal distribution is within two standard deviations of the mean.
Normal distribution
Load example data
Visualize example data
This one plots the ranked samples from our distribution against a similar number of ranked quantiles taken from a normal distribution. If our sample is normally distributed then the line will be straight. Exceptions from normality show up different sorts of non-linearity (e.g. S-shapes or banana shapes).
As an example we will create a fake data log-normally distributed and verify the assumption of normality
Correlation tests measure the relationship between variables. This relationship can goes from +1 to -1, where 0 means no relation. Some of the tests that we can use to estimate this relationship are the following:
-Pearson’s correlation is a parametric measure of the linear association between 2 numeric variables (PARAMETRIC TEST)
-Spearman’s rank correlation is a non-parametric measure of the monotonic association between 2 numeric variables (NON-PARAMETRIC TEST)
-Kendall’s rank correlation is another non-parametric measure of the associtaion, based on concordance or discordance of x-y pairs (NON-PARAMETRIC TEST)
Compute the three correlation coefficients
Test the null hypothesis, that means that the correlation is 0 (there is no correlation)
When we have non-parametric data and we do not know which correlation method to choose, as a rule of thumb, if the correlation looks non-linear, Kendall tau should be better than Spearman Rho.
Plot all possible combinations with “pairs”
To make it simpler we select what we are interested
Building a correlation matrix
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The null hypothesis (H0) answers "No, there's no effect in the population.". The alternative hypothesis (Ha) answers "Yes, there is an effect in the population.". The null and alternative are always claims about the population. That's because the goal of hypothesis testing is to make inferences about a population based on a sample.
The actual test begins by considering two hypotheses.They are called the null hypothesis and the alternative hypothesis.These hypotheses contain opposing viewpoints. H 0, the —null hypothesis: a statement of no difference between sample means or proportions or no difference between a sample mean or proportion and a population mean or proportion. In other words, the difference equals 0.
The null hypothesis and the alternative hypothesis are types of conjectures used in statistical tests to make statistical inferences, which are formal methods of reaching conclusions and separating scientific claims from statistical noise.. The statement being tested in a test of statistical significance is called the null hypothesis. The test of significance is designed to assess the strength ...
A null hypothesis is a statistical concept suggesting that there's no significant difference or relationship between measured variables. It's the default assumption unless empirical evidence proves otherwise. ... The null (H0) and alternative (Ha or H1) hypotheses are two competing claims that describe the effect of the independent variable on ...
For any hypothesis H0: q 2 0, its complementary hypothesis is H1: q 2 1 = c 0. H0 is called thenull hypothesisand H1 is called the alternative hypothesis. Based on a sample from the population, we want to decide which of the two complementary hypotheses is true, i.e., to test H0: q 2 0 versus H1: q 2 1 = c0 UW-Madison (Statistics) Stat 610 ...
Table of contents. Step 1: State your null and alternate hypothesis. Step 2: Collect data. Step 3: Perform a statistical test. Step 4: Decide whether to reject or fail to reject your null hypothesis. Step 5: Present your findings. Other interesting articles. Frequently asked questions about hypothesis testing.
The actual test begins by considering two hypotheses.They are called the null hypothesis and the alternative hypothesis.These hypotheses contain opposing viewpoints. \(H_0\): The null hypothesis: It is a statement of no difference between the variables—they are not related. This can often be considered the status quo and as a result if you cannot accept the null it requires some action.
This tests whether the population parameter is equal to, versus less than, some specific value. Ho: μ = 12 vs. H1: μ < 12. The critical region is in the left tail and the critical value is a negative value that defines the rejection zone. Figure 3.1.3 3.1. 3: The rejection zone for a left-sided hypothesis test.
The null hypothesis (H0) represents the default assumption, while the alternative hypothesis (H1) challenges it. For instance, in drug testing, H0 : "The new drug is no better than the existing one," H1 : "The new drug is superior." 2.2. Choose a Significance Level (α) When You collect and analyze data to test H0 and H1 hypotheses.
In hypothesis testing there are two mutually exclusive hypotheses; the Null Hypothesis (H0) and the Alternative Hypothesis (H1). One of these is the claim to be tested and based on the sampling results (which infers a similar measurement in the population), the claim will either be supported or not. The claim might be that the population ...
The null and alternative hypotheses are two competing claims that researchers weigh evidence for and against using a statistical test: Null hypothesis (H0): There's no effect in the population. Alternative hypothesis (HA): There's an effect in the population. The effect is usually the effect of the independent variable on the dependent ...
H0: The null hypothesis: It is a statement about the population that either is believed to be true or is used to put forth an argument unless it can be shown to be incorrect beyond a reasonable doubt. Ha: The alternative hypothesis: It is a claim about the population that is contradictory to H0 and what we conclude when we reject H0. Since the ...
Definition 8.1.2 The two complementary hypotheses in a hypothesis testing problem are called the null hypothesis and the alternative hypothesis. They are denoted by H0 and H1, respectively. Definition 8.1.3 A hypothesis testing procedure or hypothesis test is a rule that specifies: i. For which sample values the decision is made to accept H0 ...
Instead, hypothesis testing concerns on how to use a random sample to judge if it is evidence that supports or not the hypothesis. Hypothesis testing is formulated in terms of two hypotheses: H0: the null hypothesis; H1: the alternate hypothesis. The hypothesis we want to test is if H1 is \likely" true.
The alternative hypothesis is given the symbol H a. The null hypothesis defines a specific value of the population parameter that is of interest. Therefore, the null hypothesis always includes the possibility of equality. Consider. H 0:μ=3.2. H a:μ≠3.2. In this situation if our sample mean, x̄, is very different from 3.2 we would reject H0.
Intro to hypothesis testing. Write the null hypothesis H0, and the alternative hypothesis H1 (Ha). #vudomath0:00 Meaning of null and alternative hypotheses0:...
2. What is H0 and H1 in statistics? In statistics, H0 and H1 represent the null and alternative hypotheses. The null hypothesis, H0 , is the default assumption that no effect or difference exists between groups or conditions. The alternative hypothesis, H1 , is the competing claim suggesting an effect or a difference.
Here are the steps for conducting hypothesis testing: Step 1: Set up the null hypothesis: Two tails: H0: Ᾱ = μ. H1: Ᾱ != μ. One tail: H0: Ᾱ ≥ μ. H1: Ᾱ < μ. or: H0: Ᾱ ≤ μ. H1: Ᾱ > μ. The alternative hypothesis H1 is the hypothesis we want to test. For example, if we want to test whether Ᾱ is larger than μ, we set H1 as ...
Example 1: Weight of Turtles. A biologist wants to test whether or not the true mean weight of a certain species of turtles is 300 pounds. To test this, he goes out and measures the weight of a random sample of 40 turtles. Here is how to write the null and alternative hypotheses for this scenario: H0: μ = 300 (the true mean weight is equal to ...
A one-tailed hypothesis involves making a "greater than" or "less than " statement. For example, suppose we assume the mean height of a male in the U.S. is greater than or equal to 70 inches. The null hypothesis would be H0: µ ≥ 70 inches and the alternative hypothesis would be Ha: µ < 70 inches.
Hypothesis tests and condence intervals The 95% condence interval for is the set of values, 0, such that the null hypothesis H 0: = 0 would not be rejected (by a two-sided test with = 5%). The 95% CI for is the set of plausible values of . If a value of is plausible, then as a null hypothesis, it would not be rejected.
The null hypothesis H0 and the alternative hypothesis H1. Such a scenario is called the null hypothesis H0. Although it is very typical to use the assumption of no effect as null-hypothesis, note that it is really your choice, and you could use anything as null hypothesis, also the assumption: "classical music doubles the growth of plants".
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