# 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.

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17 views

### How to calculate significance when I have confidence interval and standard error?

I am very much a beginner in statistics... I have a table of nominal values about to what degree immigrants can resonate with the values of their current country. I have two tables, one which includes ...
31 views

### how can I compare if a drug affects a biological process differently than vehicle treatment

I have an experiment where I am trying to see if a drug has a biological effect that is significantly different from vehicle. Activity is measured before and after treatment. For treatment, I have ...
22 views

### Robust linear regression for group differences

I am trying to understand what it means when a p value for a grouping variable is < 0.05 after running robust linear regression. Does this mean that the 2 groups significantly differ with respect ...
18 views

### What's the population inclusion criterion in an unpaired two-sample t-test?

I'm conducting a clinical trial in London, UK on 200 women suffering from breast cancer and would like to investigate the difference in a biomarker's concentration (continuous variable) among two ...
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### What statistical test would I use with 2 groups and a control to show significant difference?

Question I would like to answer: To encourage more referrals, the product team is running an experiment on the iOS app, called “ios_referral_experiment”, that tests adding new links to the referral ...
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### t-test vs linear regression: how are standard errors calculated?

Consider Stata's auto dataset. I am interested in finding the difference in the mean weight of foreign and domestic cars. To do this, I can do a two-sided unpaired ...
92 views

### How to compare conversion rates from AB test when users visit multiple times [duplicate]

I've been asked to compute the minimum sample size for an AB test that my company is conducting for a tweaked recommender system. We will choose two groups of users, one of which sees only the A ...
63 views

### Two sample t test with equal variances hypothesis

Given a trial to test a new drug. There are 20 volunteers with some disease. The volunteers are split into two groups (10 volunteers in each) randomly: the treatment group and the control group. ...
362 views

### Can I use smaller p-value from T-test and U-test?

I want to compare two independent samples (from A/B test). T-test is most sensitive for normally distributed data (and will give smaller p-value than U-test if there is a real shift in mean value). ...
24 views

### Tests for positively skewed data with large enough samples?

I'm new to statistic tests so I need a little bit of help with them. Most of my data has distribution similar to the histogram below. As it can be seen from the histogram, the data is positively ...
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### Is it possible to specify a model without fixed effects - like a one sample ttest equivalent with random effects?

Basically, I want to know how accurate my participants are, but it would be good to take participants and items into consideration as random effects rather than having to average them out or risk ...
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### Weighted Survey Data Comparison of Many Group Means

We have a state representative sample of student data that must be analyzed using survey weights. What I am struggling with, conceptually, is what comparisons are actually possible under this design. ...
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### It is correct to compare bootstrap samples using a t-test?

I am comparing two models, I have only one accuracy per model. So I wonder, is it correct to generate for example 10.000 bootstrap samples (accuracies) and use the bootstrap samples to make a t-test ...
59 views

### When does a proxy/substitute variable distinguish between groups as well as the original variable?

I’m trying to determine when a proxy variable can be substituted for a real variable for the purposes of distinguishing two groups. To make this more concrete, suppose I want to determine, generally, ...
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### t-statistic varies widely when used for bootstrap sampling process

I have two samples of size 20 and I want to see if the difference between the geometric means is significant using two-sample t-statistic and bootstrap sampling. Here is what I'm doing ...
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### SPSS: comparing 2 variables in 3 populations

I have 2 variables, both percentages, that I want to compare across 3 samples. I want to see if the first percentage differs significantly from the second percentage, for each sample. Originally, I ...
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### Which T-test should I use?

I am studying the relationship between the level of women empowerment in politics and the level of political corruption across a sample 143 countries (both the dependent and independent variables are ...
28 views

### Which significance test is the best for measuring the response to two survey questions are significantly different?

I have a survey where there are two questions designed in a Likert Scale (1-7). Let's say: Q1: Your ratings for apples. Q2: Your ratings for pears. By counting the frequency of the likert response. I ...
26 views

### How to use proportion data for T-test and ANOVA, respectively (Non-continuous data)?

Long time reader, first time poster. I'm doing an observational study and have gotten into unknown waters in both statistics and R (beginner in both). (1) I have 2-categorical variable (species) and ...
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### Why Pearson correlation coefficient follows t-distribution?

I am trying to understand hypothesis testing for correlation coefficient. T = r√(n-2) / √(1-r^2) It is known that the statistics follow t-distribution. I saw the many similar questions but many of ...
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### t-test and p-value for calculating the difference between two fields

I am running statistical test to measure the difference between two fields (graduation age women and graduation age men). I am using ttest_ind() and I got the ...
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### Why is the between-subject effect in a two-factor mixed ANOVA not more powerful than an independent t-test?

All factors mentioned in this question have two levels. I start from the observation that the main effect of factor A in a two-factor between-groups ANOVA will generally (not always, but in most ...
1k views

### Why do I need statistical power for AB testing if my results are significant?

I have been told that I need both significance and power for my AB results to be valid. I researched a lot for this and the above statement is not making sense. I get that we need high enough power to ...
135 views

### How do I know whats my null hypothesis?

I was reading about t-tests and began wondering why the null hypothesis is chosen such that it states there is no difference between the means. The deeper question I have here is how do I state my ...
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### Successful t-test, how to analyze causality?

I have a basic question regarding t-test. I have a dataset where I observed an effect between two groups. I analyzed the effect via a t-test and the p value is sufficiently low. The data set describes ...
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### Re-deriving results of F- and t-tests produced by G*Power

In this question on stackoverflow, I asked about "programmatically" communicating between Python and G*Power in order to perform power analysis on a regression model. Here I would like to ...
35 views

### What stat test to choose

If I need to asses whether there is a change in activity( for example increase in push ups) of users after some event, which stat test should I use? Data consists of users who has 2 weeks of activity (...
14 views

### Usage of Correct T-Test

I am conducting a case-control study and hoping to look for significant differences in the mean of my dependent variable. The design of my approach incorporated 1:1 matching of controls to cases based ...
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### Hypothesis testing of test statistic, $\mu$ against $\mu <, >, \neq \mu_0$

In my notes, I am looking at a hypothesis testing of a test statistic distributed under the t-distribution because the population SD isn't known. The t score was computed for the test statistic, $\mu$,...
197 views

### Insignificant F-test in linear regression - when to stop?

I repeatedly read that one can stop looking further when the F-test is insignificant for linear regression; for example in the comments here. However, according to this very insightful answer only ...
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### Need help on running sample data analysis -

Background: I have a survey data for a year 2019 where I received 50% response rate. I wanted to compare it with 2020 data which has 65% response rate. Question being asked in the survey is to rate ...