Questions tagged [t-test]
A test for comparing the means of two samples, or the mean of one sample (or even parameter estimates) with a specified value; also known as the "Student t-test" after the pseudonym of its inventor.
466 questions
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How to choose between t-test or non-parametric test e.g. Wilcoxon in small samples
Certain hypotheses can be tested using Student's t-test (maybe using Welch's correction for unequal variances in the two-sample case), or by a non-parametric test like the Wilcoxon paired signed rank ...
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Why is it possible to get significant F statistic (p<.001) but non-significant regressor t-tests?
In a multiple linear regression, why is it possible to have a highly significant F statistic (p<.001) but have very high p-values on all the regressor's t tests?
In my model, there are 10 ...
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t-test on highly skewed data
I have a data set with tens of thousands of observations of medical cost data. This data is highly skewed to the right and has a lot of zeros. It looks like this for two sets of people (in this case ...
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Is there a minimum sample size required for the t-test to be valid?
I'm currently working on a quasi-experimental research paper. I only have a sample size of 15 due to low population within the chosen area and that only 15 fit my criteria. Is 15 the minimum sample ...
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What follows if we fail to reject the null hypothesis? [duplicate]
What conclusions can we draw if $p>\alpha$? Does not rejecting the $H_0$ mean anything?
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Significance contradiction in linear regression: significant t-test for a coefficient vs non-significant overall F-statistic
I'm fitting a multiple linear regression model between 4 categorical variables (with 4 levels each) and a numerical output. My dataset has 43 observations.
Regression gives me the following $p$-...
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t-test for partially paired and partially unpaired data
An investigator wishes to produce a combined analysis of several datasets. In some datasets there are paired observations for treatment A and B. In others there are unpaired A and/or B data. I am ...
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How should one interpret the comparison of means from different sample sizes?
Take the case of book ratings on a website. Book A is rated by 10,000 people with an average rating of 4.25 and the variance $\sigma = 0.5$. Similarly Book B is rated by 100 people and has a rating of ...
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T-test for non normal when N>50?
Long ago I learnt that normal distribution was necessary to use a two sample T-test. Today a colleague told me that she learnt that for N>50 normal distribution was not necessary. Is that true?
If ...
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How to test hypothesis of no group differences?
Imagine you have a study with two groups (e.g., males and females) looking at a numeric dependent variable (e.g., intelligence test scores) and you have the hypothesis that there are no group ...
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How to perform Student's t-test having only sample size, sample average and population average are known?
Student's $t$-test requires the sample standard deviation $s$. However, how do I compute for $s$ when only the sample size and sample average are known?
For example, if sample size is $49$ and sample ...
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How are regression, the t-test, and the ANOVA all versions of the general linear model?
How are they all versions of the same basic statistical method?
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Choosing between $z$-test and $t$-test
Background: I'm giving a presentation to colleagues at work on hypothesis testing, and understand most of it fine but there's one aspect that I'm tying myself up in knots trying to understand as well ...
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Why Levene test of equality of variances rather than F ratio?
SPSS uses the Levene test to evaluate homogeneity of variances in the independent group t-test procedure.
Why is the Levene test better than a simple F ratio of the ratio of the variances of the ...
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Can ANOVA be significant when none of the pairwise t-tests is?
Is it possible for one-way (with $N>2$ groups, or "levels") ANOVA to report a significant difference when none of the $N(N-1)/2$ pairwise t-tests does?
In this answer @whuber wrote:
It is ...
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Is there a statistical test to compare two samples of size 1 and 3?
For an ecology project, my lab group added vinegar to 4 tanks containing equal volumes of pond water, 1 control with no elodea (an aquatic plant) and 3 treatments with the same amount of elodea in ...
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T-tests, manova or logistic regression - how to compare two groups?
I'd like to check whether women and men differ on those five variables, that can be correlated with each other. The groups are also not equal with 589 females and 293 males.
The solutions that come to ...
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Which permutation test implementation in R to use instead of t-tests (paired and non-paired)?
I have data from an experiment that I analyzed using t-tests. The dependent variable is interval scaled and the data are either unpaired (i.e., 2 groups) or paired (i.e., within-subjects).
E.g. (...
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When conducting a t-test why would one prefer to assume (or test for) equal variances rather than always use a Welch approximation of the df?
It seems like when the assumption of homogeneity of variance is met that the results from a Welch adjusted t-test and a standard t-test are approximately the same. Why not simply always use the Welch ...
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How robust is the independent samples t-test when the distributions of the samples are non-normal?
I've read that the t-test is "reasonably robust" when the distributions of the samples depart from normality. Of course, it's the sampling distribution of the differences that are important. I have ...
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Group differences on a five point Likert item
Following on from this question:
Imagine that you want to test for differences in central tendency between two groups (e.g., males and females)
on a 5-point Likert item (e.g., satisfaction with life: ...
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Significance test for two groups with dichotomous variable
I have a 2x2 table with two independent groups of people that replied Yes or No in the survey:
Yes
No
Group A
350
1250
Group B
1700
3800
Could you help to find a test that can be run on these ...
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Test model coefficient (regression slope) against some value
In R, when I have a (generalized) linear model (lm, glm, gls, ...
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When to use the Wilcoxon rank-sum test instead of the unpaired t-test?
This is a followup question to what Frank Harrell wrote here:
In my experience the required sample size for the t distribution to be
accurate is often larger than the sample size at hand. The ...
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"Accept null hypothesis" or "fail to reject the null hypothesis"? [duplicate]
I'm trying to conduct a Student's t-test for a table of values while trying to follow the explanation and details found on this website. I understand that if the p-value is
<.01 then it's really ...
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Why use a z test rather than a t test with proportional data?
When testing the difference between 2 proportions why do we use a z-test rather than a t-test?
Further, is there a simple way to conduct an omnibus test for significant differences between more ...
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How to visualize independent two sample t-test?
What are the most accepted ways to visualize the results of an independent two sample t-test? Is a numeric table more often used or some sort of plot? The goal is for a casual observer to look at the ...
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Logistic regression or T test?
A group of persons answers one question. The answer can be "yes" or "no". The researcher wants to know whether age is associated with the type of answer.
The association was assessed by doing a ...
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Paired versus unpaired t-test
Suppose I have 20 mice. I pair the mice in some way, so that I get 10 pairs. For the purpose of this question, it could be a random pairing, OR it could be a sensible pairing, like trying to pair mice ...
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Should I use t-test on highly skewed and discrete data?
I have samples from a highly skewed dataset about users' participation (e.g.: number of posts), that have different sizes (but not less than 200) and I want to compare their mean. For that, I'm using ...
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Prove F test is equal to T test squared
I need to show that F test is equal to T test squared, when the T test is for 2 independent groups and assuming variances are equal.
I know that $F=\frac{MSB}{MSW}=\frac{SSB/k-1}{SSW/N-K}$
and I know ...
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t-test when the data population is not normally distributed
I understand that according to CLT the estimator would become normal but, If my population is not normally distributed, let's say it is uniformly distributed. Can I use t-test? let's also assume that ...
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How to statistically compare the performance of machine learning classifiers?
Based on estimated classification accuracy, I want to test whether one classifier is statistically better on a base set than another classifier . For each classifier, I select a training and testing ...
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Paired t-test as a special case of linear mixed-effect modeling
We know that a paired t-test is just a special case of one-way repeated-measures (or within-subject) ANOVA as well as linear mixed-effect model, which can be demonstrated with lme() function the nlme ...
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How to perform a bootstrap test to compare the means of two samples?
I have two heavily skewed samples and am trying to use bootstrapping to compare their means using t-statistic.
What is the correct procedure to do it?
The process I am using
I am concerned about ...
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Power of a Mann Whitney test compared to a t test
So a Mann Whitney U test is supposedly about 95% as powerful as a t-test when t-test assumptions of normality and homogeneous variance are satisfied. I also know that a Mann Whitney U test is more ...
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Which statistical analysis should I perform if the data sets are not normally distributed?
I am doing an experiment where there are two independent groups; one is the group of "infected" patients another is the group of "sepsis" patients. I am comparing "platelet monocyte aggregates(PMA)" ...
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Comparing two classifier accuracy results for statistical significance with t-test
I want to compare the accuracy of two classifiers for statistical significance. Both classifiers are run on the same data set. This leads me to believe I should be using a one sample t-test from what ...
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How to test for differences between two group means when the data is not normally distributed?
I'll eliminate all the biological details and experiments and quote just the problem at hand and what I have done statistically. I would like to know if its right, and if not, how to proceed. If the ...
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$t$-tests vs $z$-tests?
I'm trying to figure out exactly what the difference is between $t$-tests and $z$-tests.
As far as I can tell, for both classes of tests one uses the same test statistic, something of the form
$$\...
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Minimum sample size for unpaired t-test
Is there a "rule" to determine the minimum sample size required for a t-test to be valid?
For example, a comparison needs to be performed between the means of 2 populations. There are 7 data points ...
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Independent samples t-test: Do data really need to be normally distributed for large sample sizes?
Let's say I want to test if two independent samples have different means. I know the underlying distribution is not normal.
If I understand correctly, my test statistic is the mean, and for large ...
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Minimum number of observations for multiple linear regression
I am doing multiple linear regression. I have 21 observations and 5 variables. My aim is just finding the relation between variables
Is my data set enough to do multiple regression?
The t-test result ...
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Always use Welch-t test (unequal variances t-test) instead of Student-t or Mann-Whitney test?
I want to do an AB test to check if one version does significantly increase revenue. Generically speaking I want to test whether the central tendency (mean) of 2 groups are different from each other ...
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Equivalent to Welch's t-test in GLS framework
How can Welch's t-test be expressed as a generalized least squares model?
A standard independent samples t-test (where it is assumed that the samples being compared are drawn from populations with ...
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Normality of residuals vs sample data; what about t-tests?
An addition to the common confusion about normality testing in inferential statistics for general linear models:
I understand the assumption of normality refers to the residuals in ANOVA and ...
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Analysing pre-and-post intervention study with anonymous responses
The study I am analysing is a pre-and-post intervention questionnaire of students' views before and after studying a module. The questionnaire was distributed in three different geographical ...
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Should I use t-test on highly skewed data ? Scientific proof, please?
I have samples from a highly skewed (looking like an exponential distribution) dataset about users' participation (e.g.: number of posts), that have different sizes (but not less than 200) and I want ...
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degrees of freedom in a t-test in Kruschke's BEST paper
This question is based on a comment by John Kruschke in his BEST paper, pages 589-590.
Kruschke, John K. "Bayesian estimation supersedes the t test." Journal of Experimental Psychology: ...
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Is using error bars for means in a within-subjects study wrong?
I seem to recall one of my professors saying that error bars are completely uninformative when comparing repeated measures taken from a single group. Is that true?
Surely many studies compute the ...
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