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1answer
32 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
22 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
22 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: ...
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0answers
62 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
11 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 ...
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2answers
150 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 ...
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0answers
39 views

completely randomized VS matching - housing market correspondence test

I work in experimental economics, labor and housing market. I am trying to answer the following question: why do researchers use matched pairs of applications in labor market correspondence tests ...
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0answers
64 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
24 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 ...
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0answers
16 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 ...
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0answers
24 views

How can we measure between-experimenter reliability for experimental data?

Description of my situation: I will run an experiment in a few weeks with a total sample size of N = 70. Ideally I would prefer to have only one experimenter to collect all the data but I have to do ...
8
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2answers
235 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
323 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 ...
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2answers
108 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 ...
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3answers
169 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 ...
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1answer
120 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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0answers
60 views

Block randomization for different strata, how to achieve 1:1 treatment allocation

I am trying to randomize 60 patients in two treatments (A and B) where age will be used as strata. Since we don't know how many patients of each stratum will enter the study I have created two ...
0
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1answer
51 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
326 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. ...
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2answers
393 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
82 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 ...
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0answers
74 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 ...
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0answers
25 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
76 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
41 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
26 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
113 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
164 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 ...
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0answers
367 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
132 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
245 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
74 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
1k 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
250 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
162 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. ...
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3answers
769 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
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1answer
106 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 ...
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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 ...
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1answer
192 views

Tests for quality of permutation (Y-randomization)

Can you please suggest the metrics/tests for accessing the quality of Y-randomization (permutation)? I have some doubts in quality of Y-randomization that I am using with sample.int from R. For 100 ...
3
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1answer
772 views

Stratified randomization with permuted-block randomization

I need to create a computer program for randomizing subjects using stratified randomization with permuted-block randomization, so I want to make sure my thinking is correct: Suppose that in an ...
4
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1answer
83 views

Randomised trials: Risk of unknown confounders in large comapred to small studies

My understanding is that in a randomised trial, one aim of randomisation is to reduce the chance of baseline imbalances (i.e. possible confounding factors) between groups. Obviously known ...
1
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1answer
160 views

How to calculate the population survival probability in a two stage randomized clinical trial?

I am trying to reproduce a paper on two stage randomized clinical trials. In these clinical trials, a patient is randomized to either of the maintenance therapies $B_1$ or $B_2$ upon their remission ...
5
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2answers
75 views

Prejudice in blind test

There is a blind test that asks participants to distinguish Coke and Pepsi. A participant will test 6 cups of drink and tell whether it was Coke or Pepsi. Assuming that the participant can tell the ...
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0answers
69 views

How to choose which demographics to include in randomized trial regression?

I'm rusty on my stats. I am wondering what the prerequisites are for including covariates in my regression. I'm not looking for a prediction model but just the effect of the "treat". The sample was ...
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2answers
571 views

Why is random assignment important in stratified sampling?

Background I raised this question because of an argument I am having with a question from user697473 here. The title of his question is "Formal definiton of random assignment." In the post he ...
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3answers
687 views

Random assignment: why bother?

Random assignment is valuable because it ensures independence of treatment from potential outcomes. That is how it leads to unbiased estimates of the average treatment effect. But other assignment ...
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3answers
260 views

Formal definition of random assignment

I am looking for a formal definition of random assignment. Let $\mathbf{Z}$ be a vector of treatment assignments in which each element is 0 (unit not assigned to treatment) or 1 (unit assigned to ...
3
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3answers
818 views

How is approximately unbiased bootstrap better than a regular bootstrap with regards to hierarchical clustering?

I asked this question at BioStar but did not get a reply, so Im posting the question here. What is a simple explanation of what an approximately unbiased bootstrap is with regards to hierarchical ...
8
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1answer
364 views

How to analyse RCT where significant baseline differences exist despite randomisation?

I'm analyzing a double-blind, placebo controlled RCT using an ANCOVA in R, where the predicted "treatment effect" shows up before the treatment has occurred! The goal of the study is to determine if ...