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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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How are degrees of freedom used in the Welch's t-test to determine p-value?

I'm trying to understand using Welch's t-statistic. I'd like to compute the t-score between two distributions with different numbers of samples and different variances. The Null hypothesis is that ...
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two sample t-test for placebo adjusted values

I have a set of studies (ex: s1....s6) in which each has two arms, a treatment and a placebo. I would like to test for non-inferiority through a matrix of two-sample t-tests w/o accounting for ...
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SPSS: Paired sample t-test (pre & post) for multiple groups with data in single datasheet

I have two different groups with pre and post data for both in a single dataset. I want to do paired t-tests for group 1 comparing pre and post and also for group 2 pre and post. Is it possible to do ...
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T-test Vs. 2 Proportion Z-Test

I'm struggling to understand when it is appropriate to use a 2-proportion Z-test instead of an independent T-test. I am currently working with data where we are comparing client service hours between ...
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How can I test significant differences across multiple categories in different dataframes?

I have very basic statistic knowledge and would like to hear some suggestions to analyze my data. I've three dataframes as displayed below: ...
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Best Test for Limited Data

I'm just getting my start in learning statistics, and I'd love to be able to apply some of the tools I'm learning to my professional work. Sometimes I find it hard to determine how to apply that ...
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What type of test do I use in G Power?

I've got 1 IV with 2 levels (within-subjects) and 4 VD's (with 7 levels). What type of test do I use in this case ? Thank you
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T-Test Raw Data vs Sampling Data with CLT

I have some data that I want to run a T-Test on and get a p-value of 0.05. See below: I then using the CLT take 30 samples from each sample and take the mean of each sample. I do this 100 times to ...
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I have an insignificant beta weight of a predictor, which the only predictor in a step with significant R-square change and significant F-value

I am running a hierarchichal multiple linear regression with 4 steps containing theoretically justifyable variables: Outcome: pain rating Step 1: demographic variables (age, gender) Step 2: Pain ...
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How to run paired t-test when number of control and treated experiments aren't the same?

I'm working in a biology lab and I treat some cells with a drug (treatment) or untreated (control), then transplant them into mice. Each experiment starts with the same cells (being exposed to the ...
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linear regression backwards elimination

Suppose we have to find the best predictive linear model for the price of residential houses in a certain area from a set of predictors such as sqft, number of baths, etc. Also, suppose that we ...
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Computing the power of Welch's t-test

I constructed a Welch's t-test in order to examine the difference between the means of two samples (check whether or not one is larger than the other). $H_{0}: \mu_0 = \mu_1 ~\textrm{vs}~ H_{1}: \...
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Is there a formula to convert t-value from a regression parameter to an effect size (d)?

I've seen formulas to convert independent or dependent samples t-tests into effect sizes, but what about converting the t-value from a regression parameter to an effect size?
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Question on Task-Fullfillment in R [closed]

Yeah, so I'm working in R. And I have to check if the differences between two variables correlate with a another variable. So how do I do it? What is the command in R to check the correlation between ...
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Computing a p-value using the ratios of the means and ratios of the variances

When you have a ratio of the means ($\mu_1/\mu_2$) and ratio of the variances ($\sigma^2_1/\sigma^2_2$) from two distributions, how can you compute the p-value telling you whether the means of the two ...
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comparsion of treatment groups based on different controls

I have experimental results from two days where I wasnt able to keep the same conditions from day1 to day2, so I have two sets of data: control day1 -- 2x treatment groups day1 control day2 -- 2x ...
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Why can two subgroups from one sample be treated like two independent samples?

Assume we want to compare two subgroups of a population, say men and women, on a certain trait. We could draw two independent samples of the two subpopulations, e.g. a random sample of all men, and ...
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How to calculate the significance of a pairwise comparison distribution?

I have a variable ($X$) that depends on two parameters (say $P$ and $Q$), each of which can take six values each ($P_1\cdots P_6$ and $Q_1\cdots Q_6$). I take pairwise values of each parameter like $...
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Should I use independent T-Test in this case

I am running a test with two independent variables (Interfaces and Tasks) and one dependent variable (task completion rate): The data looks like this ...
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Minimum sample size calculation a posteriori

I am running a number of experiments where I obtain a large number of observations with one variable (yielding two sets of values; many more than would be needed for a hypothesis test). I want to test ...
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Ancova for unequal variances [duplicate]

What is the best way to compare two non-homogeinous populations (Levene's) with covariates (e.g. age). I know ancova assumes homogeneity. Is there a way around this? Many thanks
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How to test if regression coefficient = 1 [duplicate]

I’m attempting to run a regression and test whether the slope is equal to 1. Most statistical packages only test of it's equal to zero. Is there a way to bypass this ? I’ve SPSS and minitab and can ...
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Multiple T-Tests Over Time Series Data

I have 2 groups, observed for 11 months. I have observed means for each month, for each group. Running 11 t-tests, I find that 4 of the 11 months have a significant difference in their means (at an ...
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Does it make sense to include a *time-invariant* covariate in a simple pre-post analysis?

Background All participants were subjected to a single intervention and a questionnaire was issued before and after the intervention. This is a simple pre-post design. Question I can analyse these ...
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Can I draw a histogram of the mean sample distribution (n=30) sampling from my dataset (n=200)?

I would like to test whether my data reasonably satisfies the normality assumption necessary to apply a t-test. My understanding is that, to apply a t-test, the distribution itself does not need to ...
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How to use ttest and reject null hypothesis

I'm using ttest for two populations, I know that we can reject the null hypothesis when the p-value is less that 0.1 (with 90% confidence). but does it make sense to get a pvalue of say .17 and then ...
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Implement an Intercept T-Test in NumPy

Quick statistical question from an university econ student. In Stata, when you run a linear regression, they perform a t-test of the intercept coefficient to see if it is statistically different from ...
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Testing the equality of coefficients from two GMM models?

I run the same GMM model in two different samples (firms which have high imported input vs low imported input). I would like to test the coefficient estimates (particularly for fx) across the two ...
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Power of paired t-test: R vs. SAS

If we are trying to find the power of a paired t-test, SAS offers this template (among others) in PROC POWER: ...
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Control variable relevant for one group of subjects only (moderation analysis)

I'm comparing a group who read on paper and a group who read on tablet. I have data about Technology Acceptance (TA) only for the group who read on tablet. Since I don't have data for the other group, ...
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How robust is the normality assumption for two sample independent t-tests?

I'm working with a dataset where the distributions are non-normal. They are independent samples where the variances are roughly equal. Can I still run a two sample independent t-test? If not, is ...
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What's the right t-test for comparing the distribution of a response variable across two categories for the same sample?

I have data where every record has an ID, a numeric value (that represents the number of times each ID took a particular action) and a binary state that represents whether they achieved a goal. ...
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How can one variable show difference between samples, when the previous didn't? ( according to t-test)

I don't have Statistics background, and I'm trying to learn and perform some tests. I work in oligonucleotide purification, and I have two machines for that purpose. They should release the exact same ...
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Difference between regression p-values and t-test on residuals?

I'm interested in testing if a particular (binary) feature is significant in explaining a target variable, after other factors have been considered. Naively, I can do this by including the test ...
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Kindly Help with understanding following scipy ttest : ttest_ind

I am currently testing with following sample data: ''' Student t test ''' ...
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testing difference in means for multiple groups with unequal sample size and variance

My data looks something like this. I have run the ANOVA for a global test about equality of means. The statistical power and type I error are affected by the unequal sample size and unequal variances. ...
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t-Test with small sample sizes (10)

I am looking to compare the means of two sample populations of size 10. Ideally I would like to use an independent t-Test however I am concerned that the sample size is too small, as I don't know for ...
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Statistical Test to Determine an Increase or Decrease from 2016 to 2017

I have two datasets, one for 2016 (~1500 rows) and one for 2017 (~1200 rows). Both datasets have time stamps that indicate when an error occurred in a manufacturing process. For each entry, there are ...
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Appropriate statistical test for data which do not have normally distribution and do not have equal variance

My data has 150 samples and is not normally distributed, and it does not have equal variances either. I know t-test (e.g. this python method) can be used when data is normally distributed and it can ...
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Alternative to several one-sample t-tests

My dependent variable is the answer to an open numerical question. E.g. participants were asked to indicate how often within the last three months they were suffering from a headache. I want to know ...
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Advantages of using t-value as test statistic in permutation tests?

I'm working with some permutation tests where my main aim is to evaluate a treatment effect, and I have a question about choice of test statistic. I've seen that some use β for the variable of ...
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Bootstrap test of means using pooled groups - is there a problem?

In his book "Resampling: the New Statistics" (available for free online), Julian Simon presents several examples where he Bootstraps the differences in group means, assuming that the observations of ...
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How to use past attendance data to predict results of a change in time

My church has 3 services (830am, 10am, 1130am) on Sunday. I have attendance numbers for the past 9 months for each of those 3 services. The 10am service has become impacted, and the church is ...
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One-tailed Conover-Iman test?

I'm new to non-parametric statistics and want to do a post hoc analysis of some data after a Kruskal-Wallis test. I am using the implementation of the Conover-Iman test available in the scikit-...
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Is it correct to use paired t test after 1:2 matching?

Is it correct to use paired t test after 1:2 propensity score matching? How we can do this in R? I found the following link in SPSS (https://www.researchgate.net/post/how_is_paired_t-...
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How to normalize data of 0s and 1s?

the data consists of one 2, so it's not binomial. is there any way to transform it to fit the normal assumptions? I tried square root and log, both didn't work
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Comparing the mean of MSE for two models

I've estimated 2 models on simulated data and basically replicate the estimations 100 times. What I want to see is if the models are actually different in terms of their MSE. What I've done is to keep ...
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Why does a t-test on similar random samples often come out with a small p-value?

Running the following Python code, I often get very small p-values, sometimes even around 0.01. ...
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Which corrections should I use? T-test for differences in means with different sample sizes and standard deviations

I have two samples, coming from different populations. One sample has 8,000 records, a mean of 5 and a sd of 0.5 The second has 1,500 records, a mean of 7 and a sd of 1.5 The distributions are close ...
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Assumptions on the variance of the null model in one-sample Z-test?

Apologies if the answer to this is obvious, but I can't understand why the usual interpretation of the p-value (probability under the null model of obtaining a test statistic at least as unlikely as ...