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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On the specific difference between RM ANOVA and paired sample t-test

Paired sample t-test and Repeated Measures ANOVA with a dichotomous predictor are two tests that answer the same question, and output the same p-value as far as I can tell. This question has been ...
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In a paired test, what constitutes a valid pair?

The title is my question, here is a little more information. I was checking off on an analysis done by someone else and they used a paired t-test on data from the same subject; however the difference ...
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After the linear regression on the main predictors, how to include the interactions of them?

I'm currently using R to do a multiple linear regression with 7 main predictors. I've already completed the first step of regressing the dependent variable onto those main predictors. ...
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Descriptive statistics: T-test & Wilcoxon test [closed]

I am a beginner in R and I would like to compute descriptive statistics (mean & variance) for a variable of my dataset by groups (defined by another variable) for two different periods. Following ...
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35 views

Are normally distributed sample means equivalent to normally distributed residuals?

According to t-test:Assumptions "The means of the two populations being compared should follow normal distribution" The one way ANOVA test in case of 2 groups equals the t-test but the ANOVA ...
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Getting outrageously significant results when comparing two customer groups with t-test

I am trying to run some t-tests to compare census data between two groups. I have a few niggling questions and am looking for advice. Let's say I want to find significant differences between two ...
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How can I tell if my groups are well-matched?

The study design is as follows: Two Groups. Each Group was given an intervention and placebo and evaluated on a variety of measures. I attempted to match my subjects between the groups on a variety ...
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Is it okay to take the mean of p-values

I have two samples, that I cannot assume come from the same distribution, with different means and variances and different sample sizes. The sizes are very different so I iteratively subsample the ...
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What Statistical Analysis test do I run for Pre/post test?

Hello I am conducting a study where I examine patients who have not received a flu vaccination. In all I have 45 participants all who have not received the vaccine. I implemented and educational ...
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How to test significance between binary columns

I have data that looks like this: control = [0,0,1,0,1,1,0,1...] treatment-1= [1,0,0,0,1,1,0,1...] treatment-2= [1,1,1,1,1,1,0,1...] The experiment was whether or not a certain return policy (...
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t and z statistic

for normal distribution of population we generally consider n >= 30, similarly, we use t-test when sigma is not known i.e under the assumption of normality of population. Further, it is generally ...
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Test for equality of variances same as testing for equality of means under specific conditions

I stumbled on the quirk given below. I am working on two implementations, one to test for equality of means using the t-test and another testing for equality of variances using Brown-Forsythe's F-...
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Confused about the normality assumption of a t-test

I am highly confused about the normality assumption for using a $t$-test. So, as far as I've understood it when you have got $n$ iid normally distributed random variables $X_i$ you can calculate the $...
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How to compare 2 groups (control + patient) to show significant differences?

I am conducting an experimental study. I have 2 groups: The first group contains 3 healthy persons and the other one contains 3 patients (sick people). For each person of the sudy, we collect several ...
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Hypothesis testing: $H_0: \mu_1 \le \mu_2 \text{ vs } H_1: \mu_1 > \mu_2$ from two random samples

Let $X_1,...,X_n ∼ N(\mu_1, \sigma_1^2 )$ and $Y_1,...,Y_m ∼ N(\mu_2, \sigma_2^2)$ independent random samples with unknown parameters. Suppose we want to test the hypothesis: $$H_0: \mu_1 \le \mu_2 \...
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24 views

Probability that a population mean exceeds a threshold

In Googling this question, I see that there are a variety of similar tests but I couldn't find anything given the exact way I'm approaching this problem. This might be something obvious but I'm not ...
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How to compare 2 groups to show significant differences?

I am conducting an experimental study. I have 2 groups: The first group contains 3 healthy persons and the other one contains 3 patients (sick people). For each person of the study, we collect several ...
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What statistical test is good for two groups of yes/no data set?

I have to detect certain bacteria and used two methods for same 200 samples. I have tabulated two methods as below: ...
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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 ...
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38 views

Statistical model & hypothesis test

I found the following question in one of the older exam papers, Protein expression of a certain marker is measured in 2 patients groups of equal size (n=20) and at 2 different time visits. ...
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What test to use when the dependent variable is an integer but independent variable is categorical? (Data non-normal, unequal variances)

My independent variable is species (categorical). My dependent variable is the total mass of what each species ate (in grams, numerical). I want to test the difference in mass values between ...
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Fold changes (ratio) vs differences in experimental design and t tests

I'm designing an experiment to test whether a drug blocks metastasis in a mouse model system. I will have a control group that receives the metastasis activating mutation without drug and a treatment ...
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How to get beta map and t-values?

Newbie in fMRI. Recently, I learned how to get the beta values from a GLM and also getting contrast beta values from a convolved regressor from different tasks. My questions are... 1) If I do the GLM ...
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Tukey's HSD over hundreds of variables

I have a list of conversations taking place between two people. I am counting the number of overlapping words at varying points in each conversation. This has given me a long list of numbers (5500 ...
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Is it better to have more data even if it leads to uneqal sample sizes?

I am comparing two approaches A and B using a t-test. I can easily obtain samples using A since the data is generated using a simulator. However, getting a sample using B is time-consuming and costly. ...
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Statistical testing for before and after treatment of two independent groups?

I have two sets of continuous variables, weekly sales per customer. One set contains the sales of customers in the control group, and the other set contains the sales of customers in the test group. ...
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Having a hard time understanding the intuition behind regression

I am doing some research on the association of variable Y (binary) and X(discrete). When I run a ttest on the levels of Y within X, I get a non-significant association (p-value = 0.3). My friend told ...
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Comparing means of different groups over time

I hope my question hasn't been answered specifically on a different forum post. If so, please send me the link since I haven't found the exact problem I'm looking to solve. My situation is as follows:...
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Why p-values are different

I have a data of total number of mutations and fraction of mutations in each patient for three groups of patients I want to see if these three groups are different in terms of total number of ...
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22 views

What route is best for comparing diversity between 2 different sites

I am considering fungi presence and diversity in two different forest sites and looking for correlation between fungi presence/diversity and forest health. I am very new to stats, basically know ...
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What type of ANOVA or T-Test can I use for this data?

I am not very familiar with using statistical treatment and would like to ask for some help. We are conducting a study to test our constructed device and ran an experiment in which its transmitted ...
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Should I use One-Way ANOVA or Paired T-test in this data? What software can you recommend?

I am a beginner on Statistical analysis and I'm honestly not confident with the tools I'm choosing. I conducted an experiment on measuring a person's pulse rate using our project/ device and compared ...
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Regarding T-Test for point hypotheses [duplicate]

I have, so far only conducted hypotheses tests having the null hypothesis as a point hypothesis while the research hypothesis is composite. But what procedure shall I follow if my research hypothesis ...
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May each parameter's test statistics in regression be related to different distributions?

When I run a linear regression, the parameters are all tested whether they're zero using t-test. In some other regression, all parameters are tested whether they're zero using z-test. Is there some ...
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How to account for multiple measurements of same person in one-sample test?

I have 16 subjects, each with two measurements of the same variable (test score over two different sessions). I want to know if test score is different from zero. I would simply aggregate this data ...
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What statistical significance test should I use in this situation with two variables?

I have two variables: Wind speed (MPH) and passing yards in the NFL. I want to test if wind speed has a statistically significant effect on a player's passing yards. I used independent t-test from ...
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What's the rationale behind a normality test followed by a $t$-test?

Correct me if I'm wrong, but from my understanding, the standard procedure of testing whether data from an unknown source have a specific mean is to (a) perform a normality test to see if the data are ...
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Type of ANOVA that is appropriate to use in this Data

We are currently conducting a small study and have very small background in Statistical Analysis. We conducted some experiments and have gathered some data. Can anyone help me in identifying what type ...
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Sample size for stores AB testing with profit as the measurable metric

I have a group of test and control stores and I want to run AB testing on these stores to check if the proposed change in the Test store increase the profit by more than 1% from the control store. I ...
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t-test for means of daily conversion

Let's say I'm a/b testing a new site version and want to know if it improves conversion. I realize that conversion is a proportion so I would use a Z-test for this. But then I am thinking - it is ...
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How to phrase the results of a t-test?

At work, a team I'm on is researching the differences between majority-African American census tracts and all other census tracts in my county. Here is an example of one of the T-tests that I ran in ...
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Should I use Mann-Whitney U test, T-test, or something else?

I have a problem where I experimentally want to see if a fall-time for a given a triangular pyramid differ compared to a square pyramid with the same cross-sectional area. Here is the data I have. P3:...
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Test for unpaired data from the same population?

I have data from a 1 group repeated measures (Time 1 and Time 2) design to evaluate the impact of a psychological intervention for a group of participants. It is the same group of participants pre and ...
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normal distribution is essential in t test to compare two independent samples?

In student t test to compare the means of two samples, whether the normal distribution of each sample is prehypothesis or not? As we know, t test is used for comparing two independent small samples ...
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Can the null hypothesis of a t-test of “no significant difference” be used as a result?

I am not so familiar with statistics, since I am a computer science student. I hope it is alright to ask this question here. I am currently working towards the end of a thesis. I compared the User ...
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Performing t-test in binary classification problem?

I have a binary data (0 and 1) and I created an XGboost model to predict it. The data are related to insurance contracts, it is a lapse model. The predicted lapse rates are grouped by contractors age ...
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A bit confused on p values on ttest in Stata output

In Stata the output of a ttest shows p values as: Pr(T<t), Pr(|T|>|t|) and Pr(T>t) I understand the two sides to be the tails of the test and the middle ...
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Two-sample t test with before and after experiment data

I have data with the following columns: Person id, achievement before treatment, achievement after treatment (timewise) Each person is put into a control or treatment group. Because the data is ...
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How to transform two non-normal samples to perform parametric test (t test)?

I have two samples of different size (Ratio = 1:12) which are non-normal in nature. The samples are sensor values from Machine working in normal condition and when it is about to fail. I have ...
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Linear Regression: P-values of t-test of significance of regression coeficients are same as p-values of F-test about submodel

Suppose we have regression problem: $$Y = \beta_{0}+\beta_{1}X_{1} + \beta_{2}X_{2} + \epsilon \text{, } \epsilon \sim \mathcal{N}(0,1),$$ where $X_1 \sim U(0,1)$,$X_{2} \sim U(1,2)$, and we suppose ...

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