# 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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### Two way anova or paired t-tests

i am looking to see if there is a difference in dissolved oxygen levels between pool surface (S) and bottom (B) samples at four sites (an up and downstream site in two creeks). There are 3 replicate ...
1 vote
352 views

### Two-sample t-test between coefficient from regression on two different samples

I am trying to perform a two sample t-test on the regression coefficients for event dummies between two portfolio's (portfolio 1: Top portfolio and portfolio 2: Bad portfolio) The Do file I wrote for ...
45 views

### Is there any way to normalize data while keeping standard deviation?

I have two experimental groups, each one consisting of 3 independent experiments. I want to analyze the difference between them in a given characteristic, but I want to do it bynormalizing the results ...
36 views

### Thesis student statistics [closed]

My name is Manon, and I am a second-year master's student in bioengineering agronomic sciences in Belgium. I am working on a thesis due on August 12th, focusing on meliponine bees and the traditional ...
36 views

### Help for student thesis [closed]

My name is Manon, and I am a second-year master's student in bioengineering agronomic sciences in Belgium. I am working on a thesis due on August 12th, focusing on meliponine bees and the traditional ...
271 views

### T-test and ANOVA suggesting different results?

I'd like to start off by saying I am very much a beginner to statistical analyses, so I might be missing some key ideas here. Context: My study involves an experimental group and control group that ...
5k views

### Since we now have unlimited computation power (relative to historical norms), do we need to use statistical methods instead of simulations?

Allen Downey wrote a blog post in 2016 titled "There is still only one test" which discusses the advantages of running simulations over traditional statistical tests. It argues that since ...
337 views

### Single sample t-test variance assumptions for non-normal data

So I understand that a key assumption behind the single sample t-test is that the sample mean is normally distributed. This is true when the data themselves are normally distributed, and it is ...
3k views

### t-test for a non-normal population

Disclaimer: I'm a programmer. I am not a statistician. My last statistics class was (ermumble) years ago. I read t-distibution for sample mean from non normal population and while I'm sure you all ...
211k views

### 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 ...
37 views

### Why do we test on the t distribution rather than any other asymptotically normal distribution?

Following on from this question, where the answer states there isn't anything special about the t distribution for non-normally distributed data, I would like to know why the t distribution is used. ...
232 views

### Prior distribution on Bayesian T Test?

I have two subgroups of structure (bone structure) and I want to test if there is any difference of size (area) between them, and if there is, how important this difference is. The first set is a ...
162 views

### multiple t test analysis or indidivual t tests

I have to analyse samples with t tests. I am not sure if I should treat my samples as individual t tests or multiple t tests. here the details: I have an experiment where I analysed the concentration ...
509 views

### Welch t-test p-values are poorly calibrated for $N=2$ samples

I am performing a large number of Welch's t-tests (t-test with unequal variance) on very small sample sizes, often with only two samples per condition. I am finding the p-values are poorly calibrated: ...
850 views

### Normality Assumption for Independent Samples t-test

I am hoping to get some clarification on how to interpret what is often listed in statistical textbooks as an assumption of the independent samples t-test: Data are normally distributed. I had ...
99 views

### Regression with a 0-1 variable. Should be the same as running a t-test, but I get a different p-value [duplicate]

I have a dataset in R where I have volatility estimates (in my case, just standard deviation of minute returns on that day) for different days: ...
722 views

### Why is the Neyman estimator for the variance of diff in means conservatively biased?

Numerous lecture slides and papers claim that the Neyman estimator for the variance of difference in means is conservatively biased (i.e., the estimate is larger than the true variance). I must be ...
19 views

### Testing whether mean sample difference between two groups is different in two different samples

Suppose in a medical study there are the following students recruited to the study: 300 Japanese males, 500 Japanese females 600 Australian males, 700 Australian females The particular study is about ...
245 views

### One Sample T-Test - Data Transformation

I have a dataset ($n=52$) of samples that I would like to test against a known value (e.g., $5$). Because I am testing my population mean against a known mean, this would be a one-sample t-test. My ...
226 views

### Sample Size Estimation for Two Sample T-Test (Excel)

I'm trying to work out how to calculate the necessary sample size for a two sample t-test using excel and need some help. I don't think I am able to upload an excel attachment, so I will write out ...
35 views

### Is it possible to test for mean difference between groups using GLM in R?

Suppose I have a data set with the number of positives n from total tested N and I wish to test whether there's a significant difference in mean positives between males and females. If I run a GLM ...
495 views

### Running multiple t-tests across large dataset

I'm trying to work out if a t-test is the most appropriate in this situation: I have a data frame which looks like the one below but my data frame has aprox 37,000 rows. I'd like to run a t-test on ...
1 vote
305 views

### paired t-test, re: sample size calculation

We are performing a clinical intervention, that we believe will significantly improve some parameters in patients. We expect that the intervention will be successful 85% of the time (it will either be ...
518 views

### Paired T-test or Linear Mixed Model or what else?

I have measured 8 different features on the same mice on three different days. I want to compare the means of those 3 days based on the features. I have executed paired T-tests for each feature in the ...
558 views

### Which type of statistical test should I use for categorical and continuous IVs and continuous DV?

I am conducting an experimental research. Research model shown as figure. I hypothesized that X positively predicts Y. All participants were required to answer measurements of X and Y. Meanwhile, ...
1 vote
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### The F-test and the t-test reject the null hypothesis while the KS test and the Chi-Squared test do not

This is a follow-up question to How can the F-test reject the null hypothesis while the KS test does not?. Let's consider I perform the following tests: Two-sample Kolmogorov-Smirnov test (KS-test), ...
987 views

### Ranked t-test or Mann-Whitney U test for commerical A/B testing

Please help me understand how this blog post relates to this experiment. Here I try to reproduce quite old paper from Zimmerman about Mann-Whitney U test and ranked t-test (and also plain t-test) ...
42 views

### What methods to use in pre and post testing?

I am currently running a pre- and post-intervention study. My hypotheses are if the intervention has an effect and if personality traits moderate the effect of the intervention. I have an initial ...
367 views

### Testing the Difference between Two Time Series ~ Similar to paired t-test

I hope everyone is doing well. I have two time series data sets (Time Series 1) and (Time Series 2). These two series are produced monthly (from 1-2020 to 12-2020) 12 data points. Thus, I took the ...
536 views

### Multiple T Tests

On one of my questionnaires, which measure learning behaviours, after PCA, I have 4 subgroups, Efficacy/Perseverance/Effort/Achievement - I have run a T-Test and I have 4 sets of data comparing my ...
39 views

### Calculating effect size

We have conducted a systematic review to investigate the effectiveness of a treatment for a psychological disorder. We aim to report effect sizes and p values of the reviewed studies but one study has ...
389 views

### Is there any way to get correct degrees of freedom in gls, matching those of paired t-test?

I have the following data: ...
1 vote
143 views

### Preregistration of a Bayes factor for Testing an Interval Null Hypothesis

We have a hypothesis on the absence of an effect between two treatment. We would like to analyze this with the non-overlapping hypotheses Bayes factor as described here (Morey & Rouder, 2011), and ...
1 vote
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### Performing a two sample t-test for equal means on subset of a dataset

If I have a dataset that, of among other variables, contains the gender and wealth for a sample of a population with a year variable that represents the year the data about the individual was ...
22 views

### Multivariate t-test equivalent - control versus intervention

Suppose there were two groups characterised by the same dependent and independent variables. Dependent variable = time to treatment initiation - continuous. Independent variable = point of care test -...
4k views

### How can I choose between homoscedastic and heteroscedastic?

I want to calculate the p-value between subgroups of my samples. For that, I am using the T.TEST function of Excel. But I do not understand the last parameter, type: Paired Two-sample equal variance (...
574 views

### Determining statistical significance of quintile means

I have a set of physician data which I have split into 5 somewhat equal quintiles (n's range from 44-53) based on the number of "HIV_patients_diagnosed_annually". I've then created a table showing ...
33 views

### Problem regarding False discovery rate correction for multiple comparison

I am conducting research to find association of a gene with a disease. It's a case-control study. I have divided the cases into groups A and B based on genotype and controls into groups C and D. I ...
256 views

### t-test in large, unequal sample size + additional info such as effect size

I have 2 samples, named "1" and "3": (1) n = 1282, mean = 14.77, sd = 8.27 (3) n = 5360, mean = 15.88, sd = 8.55 Their distribution look: ...
11 views

### Can we use time difference as the condition to classify control and experimental group

I came across a 'study' where the 'researcher' wanted to find out whether certain personality traits (for example, conscientiousness) would influence the number of car accidents that a person might ...
14k views

### 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 ...
349 views

### confidence interval and rejection

Assume I have a data sample $X_{1}, \dots X_{n}$ from a normal distribution. Then, we consider the following hypothesis $$H_0: \quad \mu = \mu_{0}$$ and alternative $$H_1: \quad \mu \neq \mu_{0}$$ ...
3k views

### log transformation for paired t test

If my difference scores are not normally distributed - and I want to do a parametric paired t-test - do I: log transform the the original scores and perform a paired t-test on these scores log ...
230 views

### SPSS, how do I interpret statistical power for one sample t test and independent samples t test?

I did my one sample t test twice (I have two sample sizes from a survey administered (one was in one language and the other was in another language) and compared the respective means to an established ...
635 views

### Two-Sample Problem Questions

I'm just preparing for my exam, but I have no idea how to solve this problem: Durable Press cotton fabrics are treated to improve their recovery from wrinkles after washing. Unfortunately, the ...
47 views

### Can I analyse the separate items of my multi-item scale?

Can I analyse my likert scale items individually? What i mean is: I have a question with 5 statements (all on 5-point likert scale): "I feel sad", "I feel concerned", "I feel ...
1 vote
324 views

### Appropriate "semi-paired" t-test

From what I understand, the paired t-test is used when measuring the same "thing" in two different scenarios (e.g. one student's pre-test vs. post-test scores). However, is there a test that takes ...
501 views

### Variable is significant in multiple linear regression but not in t-test of the subgroups

I am getting different p-values for a variable in t-test and its coefficient in multiple linear regression so I am unsure which one to believe. As an example, my hypothetical dataset consists of ...