Statistical Analysis Stack Exchange
Statistical Analysis Stack Exchange

Questions tagged [random-allocation]

The process of randomly allocating subjects (often in the context of a clinical trial) or other experimental units into two or more conditions.

In clinical trials it is usual to try to avoid selection bias by allocating the participants using a random process which is concealed from the staff making the allocation until they have assessed eligibility. The CONSORT guidleines http://www.consort-statement.org/ for reporting clinical trials have details on how and why.

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What's wrong with (some) pseudo-randomization

I came across a study in which patients, who were all over 50 years of age, were pseudo-randomized by birth year. If the birth year were an even number, usual care, if an odd number, intervention. It's easier to implement, it's harder to subvert…
Jeremy Miles
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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. But despite this agreement and despite the …
Flask
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Should AstraZeneca's results be discounted?

This question is in regard to AstraZeneca's phase 3 clinical trial on the effectiveness of their COVID-19 vaccine. Patients were randomized to a two dose treatment group compared to a two dose placebo group. But a large portion of the treatment…
Michael R. Chernick
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Is tossing a coin a fair way of randomising a group into two groups?

So myself and my uncle are having an argument over whether a coin flip is truly random. I argue it isn't because in real terms a coin tosser will always manipulate a coin so the result isnt 50/50 therefore it is not a good choice as a randomisation…
googleplex101
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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 contrary to common statements such as the one…
Flask
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Randomisation of non-random sample

I am always a bit surprised to see psychological adverts for participating in experimental studies. For sure, people who respond to these adverts are not randomly sampled and therefore are a self-selected population. Because is it known that…
giac
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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 the treatment variable strictly exogenous,…
Robb
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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 schemes can also systematically ensure…
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Objections to randomization

In Clinical trials - a methodologic perspective, Steven Piantadosi writes (ch.13, p. 334): In Chapter 2, I noted the objections to randomization by Abel and Koch (1997) and Urbach (1993), and indicated the worth of studying their concerns and…
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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 treating a disease reduces a particular behavior.…
biomarker
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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 makes a claim that one can get unbiased estimates of…
Michael R. Chernick
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The Mediterranean diet - statistics issues with the updated paper

In 2013, a group of researchers published a paper with results on a randomized trial of the Mediterranean diet, finding that it appears to have significant health benefits. Today, they retracted their original paper because of statistical errors…
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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?
Julian A.
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Causal model assumptions - regression adjustment to experiments

Suppose we want to explain an experiment with the following model: $$Y \sim \beta_1 X + \beta_2R + \varepsilon$$ where $X$ are endogenous variables and $R$ is a randomized treatment level. To interpret the outcome of an OLS fit of this model as…
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When is there a point for using regression with controls to analyze experimental data?

Many randomized controlled trials in economics (and probably other sciences as well?) use regressions to analyze data obtained from experiments. In the simplest setup with binary treatment, assuming a constant treatment effect, a typical regression…
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