Tagged Questions

Signals situations where one is concerned about achieving intended power and size when more than one hypothesis test is performed.

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0
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1answer
36 views

How do I interpret a variance ratio test in Stata?

I need help with interpreting output from a Variance Ratio Test in Stata. $f = 1.2988$ (my variance) $\text{Degrees of freedom} = 249, 493$ I have Ho: ratio = 1 as my null Ha: ratio != 1 Am I ...
1
vote
1answer
31 views

Adjust the p-values or not?

This started as a simple discussion where everyone thought they new the answer, and ended up with arguments and dozens of paper quotations. Thoughts appreciated. We have 10 samples: Control, A, B, C, ...
1
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1answer
73 views
+100

Multiple testing in correlation analysis over time periods

I have one variable measured once per time interval (say, once per year), and another variable measured periodically (say, once per day). The periodic measurements are autocorrelated. I am interest ...
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0answers
14 views

Comparing the difference in proportions for 3 different groups

I conducted an experiment and just need some general guidance on where to go from here. I know I have to do some kind of binomial test on my data. Suppose I have the following data: ...
0
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0answers
21 views

Multiple Comparison of Standard Deviations

I have a question about comparing multiple standard deviations: To start with, let's say I have calculated two standard deviations (s1, s2) from a series of random samples. If I want to determine ...
1
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0answers
16 views

get p value based on observed F and critical F

When conducting multiple comparisons, I can calculate a critical value via whatever method is appropriate for the situation. If the adjustment method I need is a common one such as Bonferroni, I can ...
0
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0answers
24 views

Do we need to correct p-values when using multiple models?

I am currently studying epidemiology. I am writing a paper that is examining 11 disease states in one species. I am using binomial logistic regression to examine 2 possible predictors (age and ...
1
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0answers
40 views

Estimating and comparing pre-post treatment effects in multiple pairs of treatment-vs-control groups

I have a dataset from an experiment where the goal was to study in which plant ecotype a treatment with a certain bacteria had the greatest effect. Hence the data consists of a number of control and ...
0
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0answers
4 views

Null distribution of the maximum and FDR control

Suppose we have a series of test statistics $T_{1},...,T_{m}$ each corresponding to a null hypothesis $H_{0}^{j}: \theta_{j} = 0$. Let $H_{0}: \theta_{1} = \ldots = \theta_{m} = 0$ denote the ...
1
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2answers
78 views

Any other non-parametric alternative to Kruskal-Wallis?

It looks like Kruskal-Wallis is the standard nonparametric test for more than two groups. The problem is that it does not tell which groups are different, except that whether there exists significant ...
0
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0answers
27 views

Rank sums in the Kruskal-Wallis output

I use Stata to perform a Kruskal-Wallis test on four groups of data (not normally distributed), and the results are shown below: ...
0
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0answers
11 views

how can i calculate square sum of all the products of the summation? [migrated]

Rule.  The square of a sum is equal to the sum of the squares of all the summands plus the sum of all the double products of the summands in twos: But I do not know how to calculate the square of ...
3
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0answers
96 views

How to best approach ANOVA with multiple response variables that might be correlated and Bonferroni Correction

I need some help verifying a simple analysis. I have completed a simple two factor experiment of more or less equal sample sizes. Let's assume for the case of this question that the sample sizes are ...
0
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1answer
52 views

Which post-hoc is more valid for multiple comparison of an unbalanced lmer-model: lsm or mcp?

After doing a model comparison with my mixed lmer model, I have a model with three main effects, no interaction, say ...
0
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0answers
24 views

How do I report the result of an mcp-Tukey-test, i.e. how do I report it's z value?

After doing a model comparison with my mixed lmer model, I have a model with two main effects, no interaction, say signal ~ factor A + factor B + (1|subj). Factor ...
3
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5answers
160 views

What's wrong with Bonferroni adjustments

I had read an article has this title "What's wrong with Bonferroni adjustments?" for Thomas V Perneger He summarized saying that Bonferroni adjustment have, at best, limited applications in ...
4
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1answer
59 views

What statistical test is performed by summary(glht(model, linfct=mcp(factor=“Tukey”)), test=adjusted(type=“none”))?

I have data that I have fit using lme with the following structure (Subject is implemented as a random effect in order to account for multiple paired comparisons): ...
1
vote
0answers
20 views

Multiple testing, alpha, and familywise error

I am confused why it is that in multiple testing, the expected number of false positives is: $$ \alpha \times\text{number of tests}\tag{1} $$ (That is, for $\alpha = 0.05$, you would expect $5\%$ ...
4
votes
2answers
65 views

Extent of multiple testing correction

A bit of a strange question. In my fourth year biostatistics class today, we were discussing when and when not to use multiple testing correction, and the professor made an offhand comment. He asked ...
0
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2answers
44 views

Do I struggle with multiple comparisons?

I know that if there is significant difference in means among groups in ANOVA, then one can perfrom post-hoc test ( Tukey HSD or something similiar) to get to know within which groups the difference ...
2
votes
2answers
38 views

Multiple models compared over same data

My question boils down to if I really have to use a multiple comparison adjustment or not, and if so, how I can do this to retain as much power as possible. I have multiple models (say 5) that are ...
3
votes
4answers
551 views

About the Bonferroni correction

I have 50 variables in my dataset. I have correlated each variable against each variable, thus I have $49·50/2 = 1225$ unique correlations when no variable is tested against itself. Now, suppose I ...
1
vote
1answer
43 views

How to test if many samples are from the same distribution

For each day of the week I observe $n_i$ independently chosen values from some process. I would like to be able to answer the following two questions. Are the distributions from which the samples are ...
2
votes
2answers
82 views

Should corrections for multiple comparisons be used when evaluating independent experiments?

I understand why corrections for multiple comparisons (e.g., the Bonferroni correction) are used in some cases. For example, if I run a a single experiment and check significance of many factors, the ...
0
votes
1answer
37 views

Multiple testing

I am regressing different dependent variables using same set of predictors for all dependent variables such as ...
0
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0answers
17 views

How to test differences in multiple pairwise distances? With mixed model?

I want to compare two set of variables: X1 = All the pairwise distances between individuals from group A and group ref R X2 = ALL the pairwise distances between individuals from group B and group ...
7
votes
0answers
110 views

Should we address multiple comparisons adjustments when using confidence intervals?

Suppose we have a multiple comparisons scenario like such as post hoc inference on pairwise statistics, or a multiple regression, where we are making a total of $m$ comparisons. Suppose also, that we ...
0
votes
0answers
10 views

post-hoc multiple comparisons with chi squared using spss v. 22

I am carrying out an analysis using a 4$\times$2 crosstab. I found an overall significant difference but I would like to find if there are significant differences among the 4 groups. Is there a way ...
0
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0answers
17 views

column proportions comparisons for one variable

I have a one variable with three categories like marriage/divorced/widowed. The counts are: 40, 23, 7. I use SPSS in this case. I know how to perform chi_squared test for this, and it shows that the ...
0
votes
1answer
26 views

How to compare concentration ratios

I did a spectrometry measurement with the evaluation of the concentration of an element. For the element of interest I've two peaks (with normal distribution). $ C_1 ± \sigma_1 $ where $ \sigma_1 ...
0
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0answers
25 views

Multiple comparisons, multidimensional data, several groups

Could you please help me with such a problem: Let's assume I have multidimensional data that consists of 30 samples and 10 variables. This is a 30x10 matrix. I have three groups of equal size (10 ...
0
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0answers
17 views

FDR calculation on non-p-value probabilities

From a meta analysis, I have a distribution of probabilities that are not p-values (i.e., they are not uniformly distributed when H0 is true). I am using these probabilities for an intersection-union ...
0
votes
0answers
19 views

regression analysis for dataset with few predictors and few samples

I have a small pilot dataset containing experimental measurements for 12 samples, 4 numeric predictors and 1 numeric outcome variable. The goal is to obtain a first rough estimate on the extent to ...
3
votes
2answers
20 views

Multiple comparisons when investigating consistency of a device

I am trying to compare the performance of two devices designed to cool anaesthetised patients. This is a substudy analysis and the patient allocation between the groups is not even. Once cooling was ...
0
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0answers
43 views

Correcting for multiple testing on non-independent sliding windows

Question Values taken from adjecent windows in a sliding windows are corrolated. If I calculate a p-value from each window, how can I correct for the fact I have tested many windows, given that the ...
1
vote
1answer
24 views

Distribution comparison across different treatments

if I have a table like this In which, site = different sites of measurement (tissue or organ) type = different types of virus And I want to ask something about the data 1.What test can I use to ...
4
votes
1answer
45 views

What is the intuition for dependence assumption in Benjamini and Hochberg (1995)?

For dealing with multiple testing, Benjamini and Hochberg (1995) assume that the tests are independent. Benjamini and Yekutieli (2001) show that (1) the 1995 result also holds under (I think) weaker ...
1
vote
0answers
31 views

Multiple comparisons on nested subsets of data for a non-parametric test

My problem: I'm using data sets where some are nested in a non-parametric test that expects independent data sets. How can I correct for that in a way that is reasonable? Or even better: What would ...
1
vote
1answer
33 views

Difference in difference model with 2 treatment groups

I have an experiment which has 2 treatment groups(effects) and a control group. Up until this point in my analysis, I've been carrying out a DID using a regression equation of the form: Y= γD_t + ...
1
vote
0answers
73 views

MHT: Pre-Selecting statistical tests without Bias

Summary: The last formula boxed in red (which is a modified log likelihood from logistic regression) is a special non-differentiable loss function that is adapted to contain a Bonferroni correction in ...
6
votes
2answers
154 views

The meaning of “positive dependency” as a condition to use the usual method for FDR control

Benjamini and Hochberg developed the first (and still most widely used, I think) method for controlling the false discovery rate (FDR). I want to start with a bunch of P values, each for a different ...
5
votes
2answers
101 views

Why am I getting a 10-15% type I error rate for a 2 x 2 ANOVA?

While testing type I error rate using R, I found that I am getting higher than 5% false positives with a 2-way ANOVA. However, I thought one of the reasons for using an ANOVA (as opposed to multiple ...
1
vote
0answers
22 views

How to adjust for multiple comparisons with a large number of ANOVAs?

I have a complex experimental design: 3 groups, each of which come on 4 occassions and I obtain recordings from 250 skin electrodes. I am interested in knowing which of the electrodes provides a ...
2
votes
2answers
43 views

Multiple comparisons with t-test: one group with different variance

If I have 3 groups that I want to compare with a t-test (correcting for multiple comparisons afterwards) but one of the groups has different variance than the other two, should I use a Welch ...
0
votes
0answers
26 views

Comparing multiple groups to a control group

I've made several biochemistry experiments, and in which I compare several groups to a control group. I want to compare the results of 8 such experiments, so basically I have 8 measurements in each ...
3
votes
0answers
24 views

Compact letter displays with non-estimable cases

Compact letter displays are similar to grouping bars often used to display the results of a multiple-comparison procedure, but can be used more generally. You give a list of sample means (or other ...
0
votes
0answers
16 views

Iinterpretation of coefficients of multiple comparisons in a logistic regression model

I'm confused about how to interpret coefficients in relation to the reference categories. I have two variables, A and M. A is a 3-level variable and M is a 4-level variable. The reference category for ...
0
votes
0answers
38 views

Why are Dunnett's p-values smaller than those from two-sample t-tests?

Since Dunnett corrects for multiple comparisons I would assume the p-value would always be higher than a direct two-sample t-test. I came across a situation where this was not the case. Possible ...
1
vote
1answer
25 views

Combining data sets that have been adjusted for multiple testing

I have what I think is a simple question. Let say I have 5 data sets with with a variable number of tests (say 1-10K) and I control the FDR in each set to 1% using BH. If I combine these BH ...
0
votes
1answer
18 views

How to compare the nested models which each of them comes from diffrent dataset?

I have four nested models.Every of them learned from different data sets. now I want to compare these models together.normally people try to compute the F-satistics. But for my case, it's bit harder, ...