17
votes
Accepted
ANOVA vs pairwise t-tests with multiple test correction
The difference becomes clear if you understand the null/alternative hypothesis of each test.
ANOVA's null hypothesis is that the group means are the same, while the alternative is that at least one ...
- 39.6k
14
votes
Accepted
If the difference of scores is normally distributed, the sample distributions don't matter in a paired t-test, right?
You are correct. A paired t-test is conducted on the differences of the paired scores. It doesn't look at the individual scores in any way.
A paired t-test is precisely the same as a one-sample t-test ...
- 11.6k
13
votes
Accepted
Paired t-test with multiple observations per pair
Averaging the data will result in a loss information and statistical power, so it is best avoided.
Since you have repeated measures for websites, you can account the differences between websites (or ...
- 65.8k
13
votes
Accepted
Why doesn't R output for a paired t-test match the formula for a confidence interval in the t-distribution?
0.5547 is not the $t$ you are looking for. The $t$ you want to use in the equation is the critical value for the $t$-distribution with 8 degrees of freedom (n - 1).
...
- 457
11
votes
Utilising Paired T-test but data is not normally distributed and there are outliers
The paired variables are not what's assumed to be normal, but rather the differences. And for the purposes of the exactness of significance level, really only under $H_0$.
The differences won't ...
- 290k
10
votes
Paired data comparison: regression or paired t-test?
The way you set up the regression in a "correlation style" does answer a different question (which is explained nicely by @olooney).
However, you can use regressions to test for mean differences. In ...
- 6,650
9
votes
what is the difference between a two-sample t-test and a paired t-test
When you use a paired T-test, you are essentially doing a one-sample test, where your one sample consists of the paired differences between outcomes in two groups. If you create a new sample of these ...
- 133k
8
votes
Accepted
t-test for partially paired and partially unpaired data
Guo and Yuan suggest an alternative method called the optimal pooled t-test stemming from Samawi and Vogel's pooled t-test.
Reference:
Guo B, Yuan Y. A comparative review of methods for comparing ...
- 126
8
votes
Accepted
How to interpret pairs plot in R?
If you have a number of different measurements in your data.frame, then pairs will show scatterplots of between all pairs of these measures.
Example data:
...
- 8,485
8
votes
Accepted
Distribution of the pooled variance in paired samples
I'm not sure about a reference for this result, but it is possible to derive it relatively easily, so I hope that suffices. One way to approach this problem is to look at it as a problem involving a ...
- 133k
8
votes
equal *population* variances in paired t test
Any assumptions you make in a paired test would have to do with the paired differences. After all, a paired test is a one-sample test in disguise.
Therefore, NO, you do not need to assume equal ...
- 67.1k
8
votes
Can Wilcoxon be used in large sample with non-normal distribution?
I would not call n=37 large (!).
Yes, you can use a Wilcoxon signed rank test, but there are some substantial caveats. It's not suitable for all situations. Then again, the t-test might not be either.
...
- 290k
7
votes
Testing whether two data sets are statistically different
It depends on the type of statistical diffrences you are looking. It also depends upon the data distribution.
A great small table summarizing the statistical test are here with the use cases :
https:...
- 211
7
votes
How to deal with ties when conducting Wilcoxon signed rank test?
There are two obstacles to doing a Wilcoxon signed-rank test: (a) You have only 13 non-zero differences among 21. The 0 differences provide no evidence that Q1 and Q2 differ. You may hate to 'discard' ...
- 57.6k
7
votes
Accepted
Can matched samples be analysed using regression?
See my answer here for a discussion of two approaches to standard error estimation for matched samples. For a discussion on standard error and effect estimation when using matching with replacement, ...
- 36.8k
7
votes
Accepted
what is the difference between a two-sample t-test and a paired t-test
In a two-sample test, you have two independent samples. Of course, by independence, we expect the two sets of measurements will not be correlated. Sample sizes for the two samples need not be equal. (...
- 57.6k
7
votes
Paired, discrete hypothesis testing
Lazy version: permutation testing.
The null hypothesis is that their interests would be unchanged. Operationally, that means that for each student, you might as well flip a coin to pick their "...
- 834
7
votes
Is it better to perform multiple paired t-test or One-Way ANOVA test
I feel I'm making things too easy here... In addition to estimating the effect of tissues and the effect of oxygen level, you want to test whether there is an interaction between tissue and oxygen. ...
- 5,349
6
votes
Accepted
normality for extremely small sample N=5
You can't make much of a distributional assessment at n=5 -- you can (sometimes) see non-normality at n=5 -- but at such small sample sizes the non-normality has to be quite strong to have a good ...
- 290k
6
votes
Comparing two sensors timeseries that measure the same variable
Some ideas: The plot shows that the agreement is fairly good, and with your amount of data maybe you want to study the agreement with more details, not only reduce it to one summary statistic. For ...
- 82.8k
6
votes
Accepted
Paired and repeated measures! Now what? ANOVA or mixed model?
This is basically an analysis of change model.
2 measurements on each subject were taken at baseline, and 2 more at follow-up. I will refrain from calling this "control" and "...
- 65.8k
6
votes
Paired, discrete hypothesis testing
The sign test or the Wilcoxon sign-rank test present alternatives to a permutation test.
The former has really low power, but a reasonably comprehensible null and alternative hypothesis:
$\text{H}_{0}\...
- 30.7k
6
votes
Determination of sample size vs. repeated measurements in experimental design
Repeated testing of one widget will allow you to determine the magnitude of measurement variation (noise) and, maybe, if there are time or test-dependent changes in the performance. Those things are ...
- 17.2k
5
votes
Effect size for Wilcoxon signed rank test that incorporates the possible range of the attribute
The effect size statistic Z/sqrt(N) --- sometimes called r --- in the paired observations case, is related to the probability that one group is larger than the other, or if you'd rather, that the ...
- 11.6k
5
votes
Analysing pre-and-post intervention study with anonymous responses
a) Given the sample size, would running an unpaired t-test on the full
sample be appropriate? Or should I be going for a non-parametric test?
The sample size is not typically considered as "small" ...
- 12k
5
votes
emmeans pairwise contrasts result in same output values for all?
You have fitted an additive model - the fixed-effects part is condition + location. Therefore you have in fact specified that the differences for one factor are ...
- 21.3k
5
votes
Paired t-test following main effect of mixed model with missing data
With regard to the missing data, the mixed model will give you correct inferences under the more plausible missing at random assumption whereas the t-test only under the more stringent missing ...
- 21.5k
5
votes
Accepted
Sensibility and specificity with inconclusive cases (non binary problem)
The clearest answer I know of comes from "Diagnostic accuracy studies: how to report and analyse inconclusive test results" by Shinkins et al., which the STARD 2015 (Standards for Reporting ...
- 763
5
votes
Is a statistically significant difference within analytical uncertainty still valid?
Suppose you are trying to weigh a package on a scale that gives unbiased readings but is subject to variations from one weighing to the next.
If the true weight of the box is 960g and we have the ...
- 57.6k
5
votes
Accepted
Why not include random slopes in a mixed model for a paired t-test
Indeed a paired $t$-test is equivalent to a linear mixed model that you formulated as
$Y_{ij} = β_0 + β_1t + a_i + ε_{ij}; \\a_i ∼ N(0, σ^2_{subject}), ~ε_{ij} ∼ N(0, σ^2_{res}); \\i=1,2,...,n; j=1,2;...
- 2,759
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