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.

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adaptive randomization with ongoing enrollment

What is the best way to randomize existing participants at different sites in a 1:1 ratio to 2 intervention groups (group T or P) under the following conditions: Enrollment is ongoing so I’d like to ...
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How to deal with large combinations of factors

I am faced with a new problem that I cannot really tackle with the way I usually do my analyses and would appreciate any input you may have. The research goal is to identify the factors and ...
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Quasi-experiment analysis

I have 5-year sales information from a grocery store in Canada. I want to check the effect of an online campaign that happened in 2017 on food sales. My treatment group is people living in urban areas....
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Should Astra Zeneca's results be discounted?

This question is in regard to Astro Zeneca'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 ...
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Dropping Missing Observations under MAR Assumption

Some of the outcome data in my RCT data set are missing. I believe that the missing data mechanism is missing at random (MAR) as the observed characteristics significantly differ between the missing ...
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Why adjusting for randomization stratification factors in the model improves the precision of estimators for treatment effect?

I assume you will already get balanced treatment assignment within the randomization strata. Why would we still gain improvement in precision by adjusting for these factors in the model? Does not ...
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Is the difference in change an unbiased estimator of the treatment effect in a longitudinal randomized controlled trial?

Suppose I am analyzing a randomized controlled trial with a pre-post design, and I want to estimate the effect of a treatment on a continuous outcome variable. According to this paper by Twisk et al. (...
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Block design or completely randomized?

I have 5 conditions in my experiment: A,B,C,D,E and my sample size is 200 subjects. I want to have 40 subjects per condition, so I assign a condition to a person randomly without replacement. E.g. ...
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How to check if randomization was proper

Randomized controlled trial (RCT), where participants are randomly allocated to 2 or more groups and given different treatments or interventions, to evaluate which one is better, are commonly ...
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Re-randomization in Experimental Design

I am struggling to synthesize the objections to re-randomization in experiments when it is costless and the criteria are pre-specified and regression is not an option. This came up in a related ...
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157 views

Experimental Design Problem with Goofy Constraints

I am having trouble designing an experiment. I will give a hypothetical example that shares the main features of my actual problem. Suppose there are: $M$ meadows, indexed by $m={1,...,M}$, where $M \...
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How many unit are necessary in randomized experiment?

Let's say we want to conduct an experiment with binary treatment. How do I decide how many units do I need to assing the treatment to, to get internally valid results? I understand that you need to ...
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Is it possible to to have more than 2 groups for biased coin randomization? If no, is there any modifications supporting multiple groups?

Is it possible to have more than 2 groups for biased coin randomization? If no, is there any modifications of biased coin randomization supporting multiple groups? This is my R code for generating ...
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How to do randomization check?

I am struggling to find the most effective way to check randomization within my experiment. I have a single factor design with two moderators and two DVs. My IV is type of persuasion (0 direct ...
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Do I have to randomize all drug trials?

This thought experiment I came up with has been bugging me. Let's say I want to test the effectiveness of Drug A vs Drug B on reading speed (no placebo necessary). I KNOW for a fact that the effects ...
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Matching / Scoring in an Experiment, using instrumental variable (IV) regression for LATEs

Maybe this is better suited here, than in economics. I don't know and please excuse the Econ language, I cannot do any better. I did an experiment with random assignment to two treatment groups and ...
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Aggregate effects of randomized experiment

Consider the following two-equation model for observational data from a randomized experiment: (1) $y_{ij} = \alpha + \beta D_{ij} + \gamma X_{j} + \varepsilon_{ij}$ (2) $D_{ij} = \gamma + \delta ...
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Combining two studies of different types

Initial Setup In a specific experimental design, there are two treatments and two study sites. Suppose we have the model \begin{align*} Y_{ijk} = \beta^\intercal X_{ijk} + \mu_i + \nu_j + \eta_{ij} + ...
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Reference for flawed randomized controlled trial

For a seminar, I am preparing an overview of advantages and shortcomings of randomized control trials (RCT; one shortcoming is, for example, often a limited external validity). To illustrate ...
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What methods work for assigning population into groups while matching average parameters

I have $N=1000$ population size which is distributed into $K=10$ groups (A, B, C..) with a different number of people in each. Every person belongs to one and only one group. We know weight has 4 ...
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Minimization randomisation in trial, what to do if dropout or missing data?

I have been asked a question on minimization randomisation in a randomised control trial. If the randomisation has allocated thirty participants to sham or treatment, but then subsequently it is ...
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Advantages/disadvantages of fractional factorial design vs completely randomized design

I'm new to the design of experiments (DoE) and will be running a screening experiment to estimate the effect of a large number of binary independent variables (approximately 10) on a single continuous ...
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Analysing stratified random sample

Let's say I am analysing an experimental design with treatment and control group which was based on random sampling design stratified on a number of covariates. When analysing the data I see two ...
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What sample size is needed for randomization to be meaningful?

This study randomised 17 participants to 3 treatment arms. What sample size is needed for randomization to be meaningful? As an extreme example, randomly assigning 4 individuals to 2 treatment groups ...
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Controlling the allocation bias in small RCT

In order to contain the allocation bias, I would like to understand if it is possible to have a randomization process during the patients enrollement controlling ...
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Not including main effect term in subgroup analysis?

I know there are plenty of previous Cross Validated posts regarding if one must include the main effect term if the interaction term is included. The general consensus is: no if you have a very good ...
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how to do re-randomization test for trials used adaptive minimization with unequal allocation?

Re-randomization test is often chosen to validate the results from a study was randomized by adaptive minimization. In the case of of unequal allocation (like 2:1), it is more complicated because the ...
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Randomization + Power calculation for Geo experiments

Im working on performing experiment design for a retail company where we will be holding out certain markets (stores) from a treatment (say, a flyer or outdoor ads). 1) How do we perform power ...
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60 views

Does the t-test require randomization?

Can I use t test for a non-equivalent quasi-experimemtal design? As there is no randomization, can it violate the assumptions of the t-test? What statistical technique should I use?
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Balanced randomization within clusters

I was hoping someone could point me in the right direction on a randomization method. We want to randomize teachers to receive an educational intervention. The catch is that we have a number of ...
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351 views

Test for equivalence after sampling into test groups

I want to test the effects of different versions of treatment across multiple test groups of a given population. In order to do that, I want to randomly sample my population into, let's say, 4 groups ...
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Gibbs sampling allocations for time dependent observations from this model

I observe $N$ observations $\{x_{1,t_1}, \dots, x_{N,t_N}\}$ from a $k$ component Gaussian Mixture model. The $i$th observation is seen at time stamp $t_i$ and is distributed such that each $x_{i,t_i}|...
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Randomization in clinical trials

Randomization in clinical trials is a phenomena where each individual has equal chance to receive a treatment. How can you express randomization mathematically.
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Unbalanced second-wave recruitment in experimental research

I am working on a consult for a behavioral researcher's ongoing project. The current study uses three experimental conditions (A, B, & C), each with roughly-equal sample sizes (~n) at current. ...
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How does the “Carlisle method” work? (used to detect improper randomization in studies)

The NPR news article Errors Trigger Retraction Of Study On Mediterranean Diet's Heart Benefits refers to something it calls the "Carlisle method" of analyzing results of published studies to look for ...
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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 ...
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Experimental Design in A/B Tests

I want to A/B test two separate back-end recommendation logic (A and B) but I'm not sure which method works best (from a statistical standpoint). Here's how my application works: User goes to my ...
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Systematic allocation of treatment: is there a chance of biasing a design?

When we speak of the benefits of randomization, we talk about the balance of covariates so as to mitigate the possible confounding due to selection of treatment. That is, if a design were replicated ...
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How does randomisation balance known and unknown heterogeneity?

Randomised controlled trials are understood to balance known and unknown heterogeneity across groups. Beyond the a posteriori point that 'randomisation looks like it balances groups' how do we know it ...
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127 views

Best way to do block randomisation with covariates?

I have a set of $n$ objects for an experiment and I want to randomise them into a control group and treatment group with fixed sizes. I would like to use block randomisation to balance covariates, in ...
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For propensity score matching on binary outcome variables, why can the effect of treatment only be reported as the ATT instead of the ATE?

I read in this paper An Introduction to Propensity Score Methods for Reducing the Effects of Confounding in Observational Studies, that "If the outcome is dichotomous (self-report of the presence ...
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What has to be true of controls (main effects and interactions) for them to be included in experimental analysis?

Consider a simple cross-sectional regression model, $$y = \alpha + \beta \cdot T + \gamma \cdot x + \delta \cdot x \times T + \varepsilon,$$ where $T$ is a binary randomized treatment indicator, and ...
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How would I analyze this sugar-elimination Quantified Self experiment?

I'm testing whether sugar consumption is making my stomach upset, with an unknown lag. My basic plan is: Get 7 sugarfree and 7 regular, or 'sugarfull' Grape Powerades Label 14 paper bags with ...
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Assign subjects into groups so that group means are as similar as possible

I have some subjects from I have measured a variable (body weight). I want to do a case-control experiment where I will do an intervention on one of the groups (Experimental). I'd like for the group ...
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p-values for permutation tests

Let's say I want to test whether the average performance of two individuals who work together (let's say in the same room) is different to their performance when they would not have worked together. ...
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131 views

Proper statistical procedure for repeated RCTs on the same group (without replacement)

Setting: Longitudinal data on outcome Yi,t of a group of individuals, i={1,...,N}, over time, t={1,...,T} On this group, a sequence of RCTs (r={1,...,R}) staggered over time is applied. Each RCT ...
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Stratified Randomization

I am planning a trial in which I have two groups: A and B. The plan is to have 40 subjects in each group, a total of 80 subjects. There is also a need for stratification by site, where 4 sites are ...
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Using regression coefficients as primary outcome in an RCT,? Survival +frailty and Power

I'm doing a multicenter RCT for a PhD, where i compare learning 30 skills for staying calm (while suicidal) ACTIVE:with an adjunct cellphone-app training the skills and CONTROL:without cellphone ...
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Can Latin Square combine between- and within-subject design?

I´m doing an experiment and I´m not entirely sure if my design is still the Latin Square Design. I have 2 independent variables: medium and ...
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Permutation tests for sharp vs weak null hypothesis

Permutation tests provide an easy way to obtain well-calibrated tests for experimental (randomized) data for the sharp null of no treatment effect. The idea: In context where either only the ...