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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Is Bonferroni correction needed for independent samples T-test on grouped data?

I have conducted three tests (math, Biology, Chinese) on 4 groups of students who are coming from Hong Kong, Pakistan, Philippines, and Singapore respectively. I have the following dataset with the ...
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Statistical test comparing frequency (count) for one variable (categorical) with two factors

I have data of incidents where each incident is ascribed to an animal ID(s), sex, and age. Each incident is a "1" for occurrence - the data were observational and opportunistic, and thus ...
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Self-contradictory asumption of normality? Nonparametric point-biseral correltion coeffiicent? t-test or Mann-Whitney U?

A. I know from the net that for a design with one binary variable and a second variable that is continuous but is NOT normally distributed, I can use BOTH the point-biserial correlation (which is ...
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Infer from Confidence Interval of Two Sample's Mean whether they are different

Background: I have 2x8 conditions. I can visualise the 8 different cases on a continuous line (x-axis) and now want to plot the mean and confidence intervals for the 2 different treatments. The CIs ...
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How to describe in words the logical conclusion of a one-tail t-test?

Lets say we have the following null and alternative hypothesis: $$H_0: \mu = \mu_0, \; H_A:\mu > \mu_0 $$ Thus, the p-value in this situation represents the probability of obtaining test results ...
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Using z test or t test when $\sigma$ is unknown

Note: I realize similar questions have been asked here before but I couldn't find my specific doubt addressed (not in so many words, anyway). In testing a large sample for the population mean if the ...
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Statistical Analysis for mix of Categorical and Quantitative data

I have Air Freight data records for a period of 3 months that involves daily packages receiving for many companies scattered over 3 provinces, categories of materials (catalogs, docs, letters, ...
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Paired T-test when within a group there is also dependence?

As I understand with paired T-test you have two groups and there is dependence between observations of these groups but within the group, there is no dependence. How to correct for dependence within ...
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Cohen-d issues with pingouin ttest function for paired samples

I have two lists of time values, 'times0' and 'times1'. The data are paired (first value in times0 is paired with first value in times1, second value idem etc etc). I want the cohen-d of the t-test ...
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Suggestion Needed about Design Experiment

As a part of my coursework, I'm supposed to be designing an experiment for an online cab service provider to understand the following: Whether letting the cab driver know the drop location of the ...
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Aggregating Models by their t-statistics

I have several time series models $M_k$ fit on a common target $y_t \in \mathbb{R}^{T}$ and $n$ features $X^k_t \in \mathbb{R}^{T\times n}$ that are different for each model $M_k$. The models are OLS ...
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Is it ever useful to do a comparison of variance in an A/B test experiment?

Typically in an A/B test or perhaps more generally in an randomized controlled trial, we perform a comparison of means to determine wether there was an effect. However, does one ever do a comparison ...
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Find difference between sample mean of a year and population mean of the previous year?

I have the data set of the salaries of a current year and the population mean and std deviation of the previous year. I want to test if there is sufficient evidence to prove that the population mean ...
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A basic question about hypothesis test and rejection region

If we want to test the hypothesis $H_0$: $\mu = 0$, where $H_a$: $\mu \neq 0$. Then the t statistic is $t=\bar{y}/(s/\sqrt{n})$ and 95% confidence interval is $\bar{y} \pm t_{.975}s/\sqrt{n}$ by t-...
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How to prove equality of standard errors for two-sample t-test and linear regression?

Using classical linear model assumptions, we know that $$\frac{\hat \beta_j - \beta_j}{se(\hat \beta_j)} \sim t_{n-k-1}$$ meaning that the ratio of regression coefficients to their standard error ...
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t-test with data in long-format including levels of non-interesting factor in R

I've computed an ANOVA with one between-subjects factor (2 groups each including 26 participants) and 2 within-subjects factors (item type with 3 levels and emotion with 2 levels) in ezANOVA. ...
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How to test statistical difference given only median and IQR?

If I only know the medians and IQRs from samples (along with the number of samples of each population) drawn from two distributions, how to test the medians of the two distributions are different or ...
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Levene’s test for unequal sample size

Can I use Levene’s test for unequal or unbalanced sample size (wine samples of Likert 9-point scale)? If NO; which kind of test should I use (Brown–Forsythe Test; Bartlett’s Test; Welch’s T-Test, etc.)...
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What is the relationship between confidence intervals that are build with bootstrapping vs t-distributions?

I've seen a few resources online that construct confidence intervals (CI) in different ways. One is through bootstrapping which essentially samples with replacement from a group of measurements and ...
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How to test a hypothesis for mean difference within a range

Suppose we have two distributions X and Y with the mean of X greater than or equal to the mean of Y. I want to test the hypothesis that $H_0: \bar{X} - \bar{Y} <= d $ v.s. $H_a: \bar{X} - \bar{Y} &...
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ChIP-qPCR and statistics

so, recently I have been thinking about the way statistics should be run on ChIP-real-time-PCR experiments. I look in the literature, but none of the papers I could find do not tell exactly how they ...
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Hypothesis test of sample mean of non identical Gaussians

It is well known that given iid gaussians $Y_i \sim \mathcal{N}(m, v^2)$, with unknown mean and variance, then $t = \frac{\hat{m}-m}{\hat{v}/\sqrt{n}}$ follows a student-t distribution with $n-1$ ...
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How does violation of normality conditions affect p-values (relative to permutation tests)

I am running some t-tests using data from small samples (n=25) whose distributions do not appear to be normally distributed (they are not extremely skewed, but the skew is apparent in the plots and ...
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Equal Variance vs. unequal Variance for comparing Groups

I am a little bit confused about equal and unequal variances. I understand the definition and mathematics behind it, yet I don't know, for the purpose of my research, how to appropriately test that. ...
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Comparing mortality rates between two treatment groups [closed]

Would appreciate some insight on this. My aim is to compare mortality rates between two treatment groups (treatment A vs treatment B) for a given acute disease. The data goes back some 8 years (...
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Need the equivalent of a "paired T-test" for percentages (test-retest comparison between groups)

I have an observational study with a control group and a treatment group (n=25). All the subjects are given the same test (which consists of 9 questions, each of which has 4 multiple choice answers). ...
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2 answers
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Why does null hypothesis in simple linear regression (i.e. slope = 0) have distribution?

I have been reading about simple linear regression ($y=wx+b$), and I started a section when it talks about null hypothesis $w=0$. Then, when it wants to calculate p-value, they use $t-score = \frac{\...
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How to reason about infinite values in hypothesis testing?

This question might not have a practical use, as infinite values rarely, if ever, come up during data analysis, but I encountered it while implementing hypothesis tests in statistical software, ...
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10 votes
3 answers
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Is this p-hacking?

I'm currently looking into the gender pay gap using data from glass door (found via kaggle). The dataset has columns for gender, age, performance evaluations of employees, seniority, pay etc. For ...
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Log transformed (+constant) in t-test implication and result

For context, I am evaluating the level of underpricing, measured as (closing price-offer price)/offering price and underpricing suggests that the result of this calculation is positive. My H0 for this ...
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How to compare proportions by having only the mean proportion and 95%CI (reported by a meta-analysis)

I have a proportion of 31.6% (24/76) and I need to test whether this proportion is significantly different from a proportion reported by a meta-analysis study equal to 59% (95%CI: 53%; 65%). The meta-...
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5 votes
3 answers
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Do you ever test the pre-asymptotic behaviour of a variable before performing a comparison of means t-test?

I understand that it is not the normality of a random variable that matters in a t-test, but rather the fact that the distribution of the mean follows a normal distribution for large samples. However, ...
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Question On T-Statistic in Regression Example

I am reading through The Effect: An Introduction to Research Design and Causality and in chapter 13 on regression, there is a code example of calculating regression that I am not fully grasping. It is ...
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1 answer
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How to compare two groups which have been generated through subtraction of two different control groups?

I am still learning how to apply statistics properly so please bear with me (and point out) if I ask something stupid. I am sure this question has been answered already. However, I don't know the best ...
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Visualize multiple 2 sample t-tests

First time on cross validated - so if my question is not clear enough, please let me know. I have 2 groups of websites - experimental and control. Each of these groups has many float variables I ...
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What role does t-statistic play in hypothesis testing?

I'm wondering what role t-statistic plays in hypothesis testing and the interpretation of the result. In a two-sample two-tailed t-test where we have $H_0$: $\mu_A=\mu_B$ and $H_1$: $\mu_A \neq \mu_B$,...
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Cant reject null hypotheses

I am running a ttest exercise, in which I have to compare the mean of two populations. Specifically,exercise is: ttest age, by(labforce) ttest age, by(labforce) unequal In both cases, I get p-values ...
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Extremely low p-value, even though null-hypothesis should NOT be rejected

I'm doing hypothesis testing to check whether one variable affects another, by looking at the slope of the trendlines, on 268 datasets. From the analysis of each dataset (which contains many samples), ...
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Pre- and post significance analysis with random samples (independant / unpaired) for discrete (binary) metric

I am conducting an analysis where I want to check if there was a significant difference in CTR (discrete metric) when an element is moved higher in the page. The samples will be different but I have ...
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Multi comparison (e.g., t-test) for different independent pairs: is it necessary to adjust the P-value for the multi-comparison?

I kindly ask for an opinion: if I have 6 independent groups A, B, C, D, E, F but I have to compare only the pairs (A, B), (C, D), and (E,F) (i.e. there is no no cross-testing), is it necessary to ...
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Why Student's t-test doesn't require normality of population?

this PSU master's degree course says t-test can be used if either of the conditions is true: population is normal. sample size n>30. However, I read that t test is applicable when $X_{i}\stackrel{...
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Is there a way to check for the good amount of replicates for let's say T test or just mere One-Way anova (a priori)?

I have already asked this in Reddit but I really cannot find the answer I know you can check for amount of sample sizes in G power but not really for experiments. I can't be using a minimum of 100 ...
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2 votes
2 answers
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How can I confidently state the error of a specific test is within a range with a 95% confidence interval

I have a test that provides values with known amounts of error. For instance the error on the test (Value - TrueValue) = -7.62, -9.33, -8.36, -9.79,-10.45, -9.51, -10.83, -10.64, -9.96, -10.30 I want ...
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Appropriate test for two not-normally-distributed data samples

I have some data comparing training participants who experienced the same training course either face-to-face or virtually (via Zoom). I have two survey items I am comparing. Sample A is for virtual ...
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1 answer
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Why does using t-test on multiple groups of means will increase the alpha of the test?

I saw a video about ANOVA today. It said that we should use ANOVA instead of t-test when we have more than 2 groups of sample to test. This is because if we us t-test instead of ANOVA, it will be ...
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170 views

Effect size for Welch's t-test

I ran an independent sample t-test to compare two groups, student sample and Mturk respondents. The homogeniety of variance was not met (variances are not equal and sample sizes of the two groups are ...
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Comparing paired and unpaired samples

I have data from three groups of participants: Group 1, Group 2, and Group 3. Participants in Group 1 have their performance recorded on Task A and Task B. Participants in Group 2 have their ...
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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 ...
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Should I perform multiple testing correction (FDR) for all the P-values regardless if they derive from Ttest or Wilcoxon?

There are 100 participants and I want to test if 50 metabolites change before and after intervention (antiobesity drug). First, I check the normality for each variable, and then I perform a T-test or ...
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How to handle the zero deviation with Wilcoxon test and t-test(with zero standard deviation data)

I am a newbie of statistics I am looking for a statistical test for zero standard deviation data VS a distributed data Here is the example: ...
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