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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How to perform FrF2?
I'm about to perform an experiment therefore I want to use FrF2 to construct a proper experiment design. 2^6 would be a full factor design (without repetitions and replications). So far, my goal is ...
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14 views
Permutation of treatment and control groups in R program [migrated]
I would like to do blocked randomization for 120 participants into 40 blocks of 3 participants each. 2 participants within each block is assigned to treatment (denoted by 1) and 1 participant is ...
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1answer
32 views
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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18 views
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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9 views
Re-randomization for cluster randomized trial, implications for primary analysis
I am hoping the masses might have some insight or a couple papers to point to on the issue I am facing.
My research group conducts cluster-randomized trials where we assign treatment by cluster (...
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12 views
Dealing with self-selection in the treatment group
I wanted to do a Randomized Controlled Trial for a new curriculum that was announced in my area. The issue is, certain teachers, under the organisation that I'm working with, have selected to teach ...
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17 views
Stratification or minimisation…Necessary with sample sizes exceeding 250?
I was having a discussion with a statistician who developed a simple software package to do participant group allocation using the minimisation technique. In this discussion the person mentioned that ...
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1answer
32 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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21 views
How to compare odds ratios across stratified sub-groups
From a randomized controlled trial, I have odds ratios (ORs) of disease A for an intervention vs control group.
I want to see if the OR differs according to deprivation.
I plan to stratify my study ...
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19 views
How to think of compliance (and IV and LATE) in phase-in RCT designs
How should we think of compliance in a phase-in RCT design? What are the assumptions recovering the LATE by instrumental variables in this case?
Details:
In a traditional (simultaneous) RCT, in case ...
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14 views
Uncontrolled/convenience randomised allocation - is it possible?
I am currently taking part in an interventional, comparative trial with human subjects. The plan was for the study to be randomized, using stratified randomization. However there were two issues..
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1answer
25 views
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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1answer
148 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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1answer
40 views
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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18 views
How to calculate allocation imbalance in stratified randomization
I have carried out stratified randomization using 2,3 and 4 prognostic factors in r. How will I compute allocation imbalance in each of the above allocation?
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64 views
Control learning effect in experimental study
I conducted an experiment where participants drove in a driving simulator.
They performed practice runs, then a baseline and then 4 different treatment runs.
For each of the runs (baseline & ...
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31 views
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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127 views
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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1answer
74 views
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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25 views
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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1answer
74 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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1answer
881 views
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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2answers
62 views
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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1answer
18 views
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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1answer
47 views
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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368 views
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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2answers
114 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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1answer
66 views
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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23 views
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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55 views
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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1answer
128 views
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 ...
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79 views
an alternative allocation method for small RCTs?
stratification and minimization are two randomization options to achieve balance in terms of covariates or baselines in small RCTs. in recent years, researchers seem to have favoured minimization, ...
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1answer
493 views
How to analyse longitudinal data from a randomised controlled trial in SPSS using mixed effects models?
I am analyzing data from a randomized clinical trial, with 2 intervention groups (placebo and intervention) and repeated measurements over time. I am planning to use linear mixed effects modeling to ...
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2answers
66 views
Stratified sampling without sampling
At school we talked about stratified sampling regarding scientific studies.
I thought of a similar case:
Let's assume you have 4 questions for a certain number of people. Each of those people should ...
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1answer
24 views
Which of this two A/B test set-up is better?
My goal is to conduct an A/B test to compare if our new customer ranking algorithm is better than the old one in terms of conversion rate (for our call center). I have two set-up scenarios in mind but ...
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Identified latent class from experiment data
I have a large data set generated by a random experiment conducted by an online retail company. The treatment is changing the position of the text review. Specifically, in the control (default) group, ...
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1answer
71 views
Analysing an RCT with many zeros in outcome
I have a RCT to analyse – my outcome is number of days late (20 days late being the maximum). The majority of people are not late, so there are a lot of zeros in the dataset. I’m expecting that the ...
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1answer
135 views
How to get a uniformly distributed portfolio allocation vector? [duplicate]
Imagine we have a portfolio allocation vector $(x_1, ..., x_n)$ with $x_1+...+x_n=1$;
Also we assume that the vector has only elements $\geq 0$, so we have $|x_1|+...+|x_n|=1$, so no short selling;
...
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1answer
30 views
Optimal statistical method in an RCT
stackexchange.
I am doing a project, where I have conducted a randomised controlled trial. I test if I can get the same results of an already published paper, but in another setting. In my created ...
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1answer
20 views
Model choice - between subject experiment with serial dependence across time
I have done a teaching experiment where I have randomly assigned students to four different teaching style treatments for a whole semester. I have then used quizzes on a weekly basis to assess ...
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2answers
74 views
Proper analysis of partially matched, randomized design
I apologize that I can't be completely explicit because this is for review of an unpublished article.
The design involved a cluster randomized trial of a new procedure to monitor an illness. Health ...
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0answers
49 views
How to do a balance-test in a randomized controlled experiment?
Can someone explain to me how I do a balance test in a randomized controlled experiment?
Do I choose the important covariates and estimate whether there is a significant difference between my two ...
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1answer
29 views
Is it okay to include intervention usage in the model of a randomised-controlled trial?
Suppose we have a randomised-controlled trial where, for the $i$-th individual, we are given
an outcome $Y_i$
an indicator $Z_i$ ($Z_i = 1$ for intervention group, $Z_i = 0$ for control group)
a ...
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39 views
Sharp Regression Discontinuity (RD) for one part of the sample, RCT for another?
I have a study where schools' 4th graders are randomized into treated and controls (at the school level, i.e. there are treatment and control schools). Within each treated school, treatment follows a ...
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1answer
260 views
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 ...
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1answer
132 views
Assigning experimental conditions when subgroups must have the same condition
This is more of an experimental design question, but the implications are largely statistical, so I'd appreciate some help.
I'm running an experiment with traditional experimental and control groups, ...
