# 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.

2,309 questions
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### statistical significance of difference between shares

I am trying to conduct a statistical test of the difference between two shares expressed in percentage points. While I could use a regular t test if the difference was between two means, with shares I ...
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### Basic question on ANOVA vs. T-test

I'm conducting an exercise intervention with office workers. The intervention will include Yoga classes and one to one coaching. I will be looking at the effects of the intervention on two dependent ...
1answer
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### T-test unknown or known standard deviation?

One week ago I performed the following two experiments: 1) I made a tensile test on 30 steel wires. These wires have not been through a surface treatment. The maximum load is (in average) 28 Newton, ...
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### sample size to detect variability in a sample

I have a sample of continuous data which I use to build a random forest model. Now I want to determine, how many additional samples I would need to improve the prediction (reduce the RMSE by a certain ...
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### Why need wald test ( a squared version of t test ) when we already have t test?

It seems to me that they are basically calculate the same thing. Since we already have t test, why do we need a squared version (wald test)? Does wald test have its own advantage? For example in Cox ...
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### Paired t-test means that the variances of the 2 samples are the same?

Do paired samples imply that they have the same variance?
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### why can you perform t-test with the critical values of normal distribution? [duplicate]

I have estimated parameters and I want to check if they are significantly different from zero by using t-test. But since I have a large sample, I know I can compare the values with the critical values ...
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### Highly significant t-test statistics, any way to correct this?

I have been performing several paired t-test, where I test whether the sample means are different between two groups. For all of my tests (approx. 30), which all carries 13-14,000 observations, I ...
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### Potential problem in using paired t-test or Wilcoxon if the two samples consist of multiple draws from same group?

I have an experiment that works loosely works as follows: There are ten subjects in each treatment. There are two treatments, A and B. Each treatment has 8 rounds. In each round, each subject is ...
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### Go with t-test or Mann-Whitney U test?

I'm measuring performance of 2 methods (method_A and method_B) that try to satisfy customers demands. Both methods produce ...
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### Proper analysis procedure of paired rate comparisons - ratio or difference?

I have a set of population counts where each row represents a different region, and variables show overall counts and counts/percentages within specific groups/criteria. I am interested in the cross-...
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### regression basic doubt

If have a simple bivariate regression model: $Y_i= x_i \beta + \epsilon_i$ where $i$ are the number of observations. How do I test for the hypothesis that the OLS coefficient $\beta$ does not ...
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### Statistical significant difference between two regressed models with use of confidence intervals

I wonder how to decide if two regression models are significantly different at a location X. Here is an artificial example, $\hat{Y}=a+b\cdot X+c\cdot X^2$. The graph shows the (artificial) measured ...
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### Non replicated vs replicated field trial

I need to conduct a pesticide efficacy trial on avocados. I have been asked to describe two different trial approaches: replicated and non replicated. I have drawn the two trial design options. ...
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### Does the t-test require randomization?

Can I use t test for a non-equivalent quasi-experimemtal design? As there is no randomization, can it violate the assumptions of the t-test? What statistical technique should I use?
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### t-test -> validity?

As I had a meeting with my supervisor for my thesis write up she did mention 3 techniques to add for my data. a) Cronbach's alpha for the reliability b) t-test for the validity and c) correlation ...
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### t-test result, what can I say about the data?

Suppose I run a t-test and I get the following result: The p-value is very small, so I reject the null hypothesis. However, I was wondering if I could say something on the sign of two mean and their ...
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### Likelihood ratio to quantify the similarity between one sample with two other matched samples

I conducted a study with 3 conditions and N subjects. All subjects performed all conditions once. I would like to know if the first condition is similar to the second or third condition. Formally, ...
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### ANOVA or T-TESTS on Z-SCORED data

Let's assume that we have results from X people for 3 different variables. The scores are not on the same scale (for example they're not scores on the test when you can simply reach from 0-10 points). ...
1answer
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### If sample standard deviation is biased, why do we use it in typical mean tests? [duplicate]

If sample standard deviation is biased, why do we use it in typical mean tests? Why do we not use an unbiased estimator by dividing the sample standard deviation by C4?
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### Inconsitency in comparing log-likelihoods of z- and t-values with appropriate distributions?

I am working through "Glen McPherson: Applying and interpreting statistics", where he introduces the t-distribution on p.125. As a small experiment i tried to do the following (pyhton, scipy, numpy, ...
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### Best statistical method should I use to calculate p value?

I'm comparing two different populations with unequal variances and non normal distributions using python. For sample #1 I'm drawing a random sample of n=30 from a population of 200. For sample #2 I'...
1answer
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### Resource for an explanation of Sample size calculation when $\alpha$, Power and Effect Size for t-Test are given

For a simple z-Test or t-Test (one-sample or two-independent-sample with $n_1 = n_2$ and equal variance) I want to calculate the required sample size $n$ when the significance level $\alpha$, power ...
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### Minimum Population Size for T-Test

I'm comparing two different populations with unequal variance and non normal distributions. For sample #1 I'm drawing a random sample size of $n=30$ from a population of 200. For sample #2 I'm ...
2answers
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### Using wilcox.test() and t.test() in R yielding different p-values

This is a repost from the R forum, as I was told to post here instead. I would like to test whether there's a significant difference in the mean between this two samples: ...
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### Using wilcox.test() and t.test() in R yielding to different p-values [duplicate]

I would like to test wether there's a significant difference in the mean between this two samples: ...
0answers
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### T-test with conditional data

I have some data giving the vital signs of people before and after one experiment. Also for each single measurement I have some informations about the subject that could affect the results and need to ...
1answer
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### What does p-value of Mann Whitneyu t-test equal to 0 mean?

I'm trying to perform Mann Whitneyu test on a dataset. As the code is shown below, the data is grouped by different Medal value. Why the result p-value is 0? ...
0answers
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### Using a paired t-test on panel data

I am working with a data set containing approximately 100 students who have all been tested before and after and intervention. I am now going to test whether the intervention has had any impact on the ...
1answer
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### Which formula for t-test is correct?

When Population variance is unknown and n<30 we use t-test. x=sample mean, u=population mean, s=sample standard deviation, In my book and on many online websites i found t-test formula to be t=(...
1answer
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### Paired or unpaired t-test and Wilcoxon signed rank test?

I am having a conceptual problem, of not being able to grasp whether my data is paired or unpaired. I have to test for the mean and median differences between two sets of data: SBP and GICS (see ...
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### Using a t-test to follow-up on a non-significant interaction in an ANCOVA?

My question is about whether a t-test can be used to follow-up on a non-significant interaction found with an ANCOVA. I have an experiment that compares the impacts on students' learning (as measured ...
1answer
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### Does normalisation of paired data affect a t-test?

Say I want to compare some measure before and after a treatment. To my understanding, I should use a paired t-test. But, if I manually normalise the data so that each before measurement is 1 and each ...
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### Can differences in predicted values before and after events be detected by comparing residuals?

My data consists of 30 variables taken together at irregular intervals. They are taken at least 200 times each for at least 100 different subjects. I am assuming that 5 of the variables can be modeled ...
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### Local significance of composite anomalies

Suppose I have the following 20 points: ...
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### One tailed paired t-test

Ok, this might be an obvious question but it's had me stumped. Let's say we're doing a test to see the improvement on test scores before and after some process. We could state the hypothesis as: H0:...
1answer
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### how to interpret this t result?

Two Sample t-test ...
1answer
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### Hypothesis testing control vs treatment when the outcome tends to vary over time

I want to test the effect of a treatment on a continuous outcome (specifically interested in increase in average in the treatment group). The experiment is run over a period of time. But the problem ...
1answer
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### Power calculations

I am using a toy example to explain power calculations for a t-test Let's say we have two populations where we measure a certain parameter. Population A has a mean of 0 and population B has a mean of ...
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### Can a coefficient technically operate as a test statistic?

This is somewhat pedantic, but a debate I've had is whether a regression coefficient can technically operate as a test statistic. It's not being claimed that this is the normal setup or a better way ...