What is T-test: Definition and 20 Discussions

The t-test is any statistical hypothesis test in which the test statistic follows a Student's t-distribution under the null hypothesis.
A t-test is the most commonly applied when the test statistic would follow a normal distribution if the value of a scaling term in the test statistic were known. When the scaling term is unknown and is replaced by an estimate based on the data, the test statistics (under certain conditions) follow a Student's t distribution. The t-test can be used, for example, to determine if the means of two sets of data are significantly different from each other.

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  1. TytoAlba95

    The t-test and the central limit theorem

    Ans is 3. I know basic t-test but I have no clue to solve this question. Thanks.
  2. Conservation

    I Nonparametric Hypothesis Tests

    Hello everyone, Say you have two sample distributions that are known to be two different distributions (one randomly drawn from a Poisson distribution, other randomly drawn from an uniform distribution). Given that you know the distributions are not going to be normal, a two-sample t-test would...
  3. Vital

    I Degrees of freedom for t-test for 2 samples, 2 variances

    Hello. I will be grateful for your help in finding the logical meaning of each part of the formula of degrees of freedom, which are computed for a t-test when variances are unknown and are assumed to be unequal. Please, take a look at the formula, the way I managed to understand some parts of...
  4. T

    I Is the Definition of Unpaired t-test in My Book Correct?

    I was reading a book that said: Unpaired t-test is applied to unpaired data of independent observations made on individuals of two different groups (of a single sample) or samples drawn from two populations. Now what wiki says is that they are not unpaired the e.g. given is one with 50 and 50...
  5. M

    MHB Investigating Reading Comp. w/ Cultural Capital: A T-Test

    Hey! :o The international comparative school performance study PIRLS (Progress in International Reading Literacy Study) raised in 2011 the reading competences of the fourth graders in more than 40 countries, mong others in Germany. They would now like to investigate how the cultural capital of...
  6. ElijahRockers

    Neurologist: What P-values should I be expecting?

    Inexperienced data analyst here with a real-world example, I have attached a zip-file with screenshots and p-values of the following data. The "reference regions" are Cerebellum White, Cerebellum Gray, and Temporal Cortex. The top-most graphs depict the curves in the indicated region for young...
  7. S

    T-test: normal probability plot

    I'm studying statistics from the book "design of experiments" by Montgomery and about the t-test it's stated it is necessary to check the samples are described by a normal distribution throughout a normal probability plot and I have noticed the y-scale is not familiar to me, it's neither linear...
  8. Mogarrr

    Understanding the Power of a t-Test

    I'm looking over my notes, and I'm puzzled by this non-central t-distribution, and why it is the alternative hypothesis. Non-central t-distribution: If X \sim (\delta, 1) and Y \sim \chi^2_{r}, in addition if X and Y are independent random variables, then \frac {X}{\sqrt{\frac {Y}{r}}}...
  9. M

    MHB Visualizing Data, Significance Level, T-test, Level of Measurement

    Hello. I was just wandering if anyone could help. I've been doing a couple of statistics questions, and when they ask for some questions, I am not sure if I have an appropriate understanding of what the right answer should be. I would really like to understand this material, so what I want to...
  10. S

    Can Hedges' g be greater than 1 for paired t-tests?

    Can Hedges' g (effect size) for a paired t-test be greater than 1 if the following is the formula for g? g = (mean_1 - mean_2)/(average standard deviation of the two variables) Thank you.
  11. D

    State null and alternative hypothesis for 2-sample t-test

    Homework Statement A new type of medical tubing is being developed by company ABC. The development engineer would like to test whether the tube has better elongation than the competitor's design. State the hypotheses that should be tested in this experiment The Attempt at a Solution...
  12. L

    Should I take the absolute value of a negative t-test statistic?

    I have calculated the one sided t-test statistic and am getting a negative value as the sample mean is less than the mean under H_0. there are no negative t values in the table - do i take the absolute value of this? thanks
  13. C

    Question about two sample t-test (unpaired)

    I have read that the statistic computed for the unpaired two sample t-test is: t = \frac{\bar{x} - \bar{y}}{\sqrt{SEM_x + SEM_y}} where: SEM_x = \frac{\sigma^2_x}{n_x} (and likewise for y). Part of this makes sense: it is satisfactorily proven to me that that Var(\bar{x} -...
  14. R

    Mathematical Statistics- two sample t-test

    Homework Statement At the 5% level, will the two means be equal ? Homework Equations The Attempt at a Solution I tested the variances and found out that it's very likely that the variances are equal, so this is an assumption we make when we do the second test. Now, I'm trying...
  15. S

    Using a T-Test for Correlation in Biology Report

    Homework Statement Hello everyone! I have been trying to figure out what i should do to show correlations in my biology report about smoking and heart rate. I have conducted 41 trials with people who are -Non smokers and exercise -Smokers and exercise -No exercise smokers...
  16. N

    Are These T-Test and Effect Size Calculations Correct?

    Hello! I hope it's okay to ask stats questions... I think the calculations are correct, but I would appreciate it if someone could check for me! These are the results from the exp. using repeated measures. My hypothesis is that the reuslts in condition 2 should be less than condition 1. Cond...
  17. M

    The Student T-Test (Two tailed)

    My bio teacher is basically a dumbass. He doesn't teach us anything (literally) and gives us a test. Just yesterday we had to do a lab for him and we had no outline, (just said look at your handout, and I see that I have 20, with a rat on it and showing me how to make a graph on excel, real...
  18. C

    Does anyone know how to perform a statistical T-test?

    Does anyone know how to perform a statistical T-test? I have a set of data and I want to do a T test, but I'm not sure how to do one. Can someone give me instructions or let me know of a site that gives instructions how to do it? Thanks.
  19. A

    A student's confusion over Student's t-test values

    Hello, I've been working on this assignment for the past while, having to do with independent t-tests and the like. I have two major questions that I can't wrap my head around: - When looking at the critical values of Student's t distribution table, what do you use as a critical value if...
  20. B

    Calculating a Paired t-Test Equation

    What is the equation for a paired t-test?