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16 views

Can you exclude one country as robustness check in multilevel cross-country model?

I am conducting a multilevel study in which individuals are nested in countries. As a common robustness check in normal linear regressions, we can exclude one or a few countries with special ...
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0answers
15 views

Random Sampling Techniques

I have a pool of people who each have at least one email associated to him/her. Two people can also share a single email. This results in clusters of people chained together by email:person units. ...
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27 views

Why would one not stratify random assignments in a controlled trial?

With some frequency I read reports of randomized controlled trials where, despite the randomization, a baseline survey found significant between-group differences in important covariates. It seems to ...
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0answers
89 views

Sample size and power calculations for a randomized controlled trial

I need help with the power calculations to determine the sample size of a randomized clinical trial. This is a relatively simple trial with two arms: an intervention arm and a control arm. Patients in ...
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0answers
25 views

If 4 Peaks is GA-friendly, why is it getting stuck in a local optimum?

First, 4 Peaks: Given numbers N and T, an instance of 4 peaks,x, is an N-length bit string. We rate its fitness by doing o(x) = Number of leading 1s, z(x) = number of trailing 0s. An extra REWARD=N is ...
2
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1answer
69 views

Advantages of counterbalancing vs. randomizing stimuli

I'm designing an experiment, in which 40 participants answer 10 questions, 5 in condition $A$ and 5 in condition $B$, and I'm interested in the difference between the two conditions. It's not clear ...
3
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1answer
47 views

Is this a Random or Purposive Sample? Inclusion-Exclusion Criteria and the Sampling Frame

Introduction I am confused about when a sample is a random sample (i.e. probability sample) and when it is a purposive sample (i.e. non-probability sample). My understanding is that the former allows ...
2
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0answers
12 views

What is re-randomization?

I'm a statistics newbie, taking an online course, and the term "re-randomization" was thrown in without explanation. What does it mean?
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0answers
18 views

Randomization for multi-site clinical trial, screen failures

Two questions about appropriate randomization procedures for a small two-armed trial at 3 sites. About 100 participants total, evenly split between study arms. First, we are concurrently enrolling ...
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0answers
32 views

Comparing the Magnitude of the Difference in Variances Between Groups to Identify Selection Bias

I'm comparing two populations--private and public sector accounting firms in the state of Rhode Island--for differences in the distribution of quality/ability of the accountants who work at those ...
3
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3answers
39 views

how to include distance buffers in cluster randomized trial

I need to incorporate distance buffers into the selection of treatment and control units in a randomized-controlled trial in order to minimize spillovers between arms. Cluster in this study is a ...
1
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1answer
54 views

Can confidence interval from hypothesis test inversion ever contain observed difference if that difference is significant?

My question concerns the method for constructing a confidence interval for a difference in means based on a randomization test (that can be found here , check under 'Confidence interval based on the ...
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0answers
24 views

Principles for choosing randomization procedure - example from tournament data

I have read many very useful posts on this site as regards randomization procedures. I wonder if the following example may be useful for discussion purposes. My basic question is which of two ...
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1answer
53 views

Randomization software/service for clinical trial

I need a software/web-based system for the clinical randomization. This software/service should have the capabilities for handling stratification, multiple centers and block. The sample size of ...
1
vote
1answer
35 views

Is it possible for two independent people to generate randomness?

It is well documented that people are not very good at generating random sequences. However, is it possible that two people, working independently, could generate randomness together? Consider the ...
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0answers
108 views

How is the constant in Marsaglia's xorshift* RNG determined?

I get Marsaglia's basic xorshift RNG. For further randomness he suggests multiplying the result by a "suitable constant." This is some code I've found that does just that: ...
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0answers
26 views

Generating a dataset from mean, standard deviation, n and 95% CI

I have the output of a couple of Socprog models and I'd like to see if the results are statistically significant. Group A output: ...
3
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0answers
66 views

What kinds of PRNG exist outside Linear congruential generators?

I'm kinda running out of words, Linear congruential generator are really low quality PRNG but it was all I needed for some basic stuff, now I need to fill the blank and get to know other families of ...
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0answers
14 views

Correcting for multiple comparisons using simulated distribution

To check if unilateral pairs (defined below*) are coordinated (i.e. move together) in a flock of N coordinated individuals, we generate hypothetical (null) distribution of a certain focal parameter of ...
5
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2answers
286 views

Test the randomness (uniformly distributed) on a 64 bit float random generator

We have a random number generator which is supposed to generate 64 bit floats, uniformly. We want to test whether it is a good uniformly random. I am not asking the general way to test it, as it was ...
2
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0answers
70 views

Randomization test and comparisons of many to 1

I have about 80 different groups, each with 3 replicates which I would like to compare against a control having always a value of 1. As I have a low number of replicates and many groups having 2 ...
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0answers
25 views

Randomization Testing help

I am scratching my head over this one...any help would be greatly appreciated. I want to know if the average travel time between Guell Park and the beach in Barcelona using the bus or the metro ...
4
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1answer
29 views

Randomisation for 2 site clinical study

If I want to conduct a randomised study in 2 sites comparing two clinical treatment arms, and every site is expected to include 60-80 patients, is it acceptable to randomise every new patient with ...
8
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2answers
317 views

Using control variables in experiments?

Why would one want to control for any number of baseline covariates in a situation where the assignment to treatment group is random? My understanding is that randomly assigning treatment should make ...
5
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1answer
387 views

How to calculate permutations of categorical variables with R

I want to simulate or calculate probabilities of combinations of group membership for different sample sizes (e.g., n= 3, 4, 5, 10, or 100) for two groups (of the same sample size). Each outcome could ...
2
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2answers
131 views

Does randomization really allow us to make claims of causality?

Lets say two groups are compared. Subjects are randomly assigned to each group, then a treatment is given to half while a placebo is given to the other half. All aspects of the experiment (order of ...
4
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3answers
181 views

Question re permutation tests for a relatively complex data set

I regret that I cannot be overly explicit due to confidentiality agreements. I will try to state my problem by analogy. Suppose that you have two groups of people, one with a condition and one ...
0
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1answer
207 views

MULTIPLE TESTING: Probability of specific outcomes from MULTIPLE experiments using randomized data

This is a follow-up question to this one: Significance test across multiple simulated experiments There's one answer I'm leaning towards accepting, but I wanted to make sure I understood how ...
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1answer
52 views

Calculating the probability of 31 of 628 items are sampled (no replacement) more than 10x amongst 150 participants drawing 50 items each

I am sorry for having to ask a simple probability question, but I have been thinking about it for weeks and an extensive google search has given no answers. I have a group of 628 questions. 31 ...
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2answers
425 views

Is randomization reliable with small samples?

Jerome Cornfield has written: One of the finest fruits of the Fisherian revolution was the idea of randomization, and statisticians who agree on few other things have at least agreed on this. ...
8
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3answers
458 views

What examples of lurking variables in controlled experiments are there in publications?

In this paper: Lurking Variables: Some Examples Brian L. Joiner The American Statistician Vol. 35, No. 4, Nov., 1981 227-233 Brian Joiner claims that "randomization is not a panacea". This is ...
2
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1answer
135 views

How to get proper randomization in website A/B testing?

In the statistical practice of experimental design, you separate your tests by 'blocks' if you can control the factors (say routing to one page or another, or categorizing by browser) or through ...
2
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0answers
88 views

$p$ value for a randomized test

For a randomized test, how do we compute the $p$-value? For example, suppose the test is of the form: $\phi(X)=1$ if $X > c$, $\phi(X)=p$ when $X=c$ and $\phi(X)=0$ otherwise. How do we compute the ...
2
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0answers
28 views

Confidence interval(s) for randomization design

I am developing a method to do something with permutation testing. I have two permutation / randomization schemes and do not know which one is better than the other. Can I find the confidence interval ...
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0answers
69 views

Statistical significance problem

I've got an algorithm which assigns a score to a list of individuals (nodes). I want to discover which nodes received a statistically significant score. So I "randomized" the algorithm in order to ...
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1answer
100 views

How do I randomize a larger population, from an existing population in R?

I have a small 20k (176 variables) test dataset. I want to create a random bigger dataset for testing, using the rows (data) and columns (names) from the small dataset. Currently I have: ...
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1answer
42 views

How to test whether variables are more frequently associated than expected by chance?

I have this presence/absence matrix (S2 is missing on purpose). ...
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0answers
31 views

Picking and permuting over randomized reference set from large amount of data

I have a question about different strategies for randomly picking up a reference set for statistical testing from a large amount of data (and permuting over the random picking/testing). For ...
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0answers
125 views

How can I tabulate (data layout) the following randomized block design?

Suppose the experimenters are interested in how weight gain in rats is affected by different sources of protein: Beef, Cereal ...
2
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2answers
224 views

Completely random or structured selection of receipients for an A/B mailing

and apologies if this is an overly simple question. I am doing an A/B mailing (where we send out two different solicitation letters). It's going out to past donors so we have some information on them ...
3
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0answers
577 views

Permutation test comparing a single sample against a mean

When people implement permutation tests to compare a single sample against a mean (e.g., as you might do with a permutation t-test), how is the mean handled? I have seen implementations that take a ...
4
votes
1answer
150 views

Testing for non-random overlap of polygons

I have two polygon shapefiles and I want to see to what extent the observed amount of overlap is due to chance. I'm thinking of some kind of permutation test, but not sure of the best way to ...
5
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2answers
388 views

Homogeneity testing of baseline characteristics in medical trials

I have been reading medical journals and they repeatedly show baseline characteristics of samples from a randomised controlled trial, which they have then tested to ensure no differences between the ...
3
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0answers
78 views

Analysis of randomized experiments

I have data from an experiment in which participants were randomly assigned to one of two groups and asked a series of opinion questions. One group, the control, was not presented with any additional ...
6
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2answers
2k views

Difference between Randomization test and Permutation test

In the literature the terms Randomization and Permutation are used interchangeably. With many authors stating "Permutation (aka randomization) tests", or vice versa. At best I believe the difference ...
1
vote
1answer
376 views

How to perform randomization test for categorical data and/or chi-square?

I am very newbie in statistics and I my problem is as follows: I have a total set of 20,000 categorical observations (this is my whole dataset, say DATA1) which has a certain proportion of "yes" and ...
2
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1answer
198 views

Randomization Tests

The following data are mandible lengths (mm) of 10 male and 10 female golden jackals Canis aureus in the collection at the British Natural History Museum. The two samples are independent. ...
19
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3answers
857 views

What's wrong with (some) pseudo-randomization

I came across a study in which patients, who were all over 50, were pseudo-randomized by birth year. If birth year were an even number, usual care, if an odd number, intervention. It's easier to ...
2
votes
1answer
142 views

How does randomization testing for correlating two variables work?

I was going through OpenIntro Statistics[http://www.openintro.org/stat/textbook.php] and came across two case studies in the first chapter Discrimination against women during promotion - Page 42 ...
2
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0answers
36 views

In a random selection of addresses, determine if users are unable to access one of the addresses

Our client software randomly selects a server to connect to. There are four separate addresses the software randomly chooses from. Two addresses are "old" and two are "new". As many firms need to ...