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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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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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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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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13 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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24 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
53 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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38 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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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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44 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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How to test for a reduction in gendered language? What would the outcome variable be?
Say I’m looking at dating website profiles. I note 20 adjective that are much more likely to be used on females’ profiles than males’ profiles. I note another 20 adjective that are much more likely to ...
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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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106 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
63 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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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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64 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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710 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
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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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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
40 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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331 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
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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
53 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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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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47 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
100 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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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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401 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
65 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
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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
110 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
23 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
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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
71 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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35 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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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
237 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
124 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, ...
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1answer
114 views
Difference in estimating treatment effect in experiment using regression with covariates and assuming the data come from stratified experiment?
Assume I only did a completely randomized experiment (CRE), i.e., $N$ subjects, I randomly assign $N_t$ (say $N_t=N/2$) of them to the treatment group and the rest to the control group. Now, after I ...
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1answer
47 views
Randomizing again after unbalanced covariates
Assume you want to perform an experiment in order to assess the influence of a treatment on the outcome.
You randomly allocate treatments to subjects, e.g. by using a random number generator (in R: '...
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1answer
203 views
The implications of non-random allocation of intervention
I'm trying to understand the implications of an intervention which is not randomly allocated in a quasi-experimental setting. The intervention is receiving a license for shale gas exploration in the ...
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2answers
171 views
treatment effect in instrumental variables regression
I'm designing a randomized encouragement trial in which half of the sample will be randomly assigned to receive a special invitation to try a new intervention. This design will likely result in two-...
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1answer
112 views
Details of randomized block assignment for RCT
I have been tasked with designing an RCT and although I am familiar with the general principles of randomized block designs, I wanted to hunt down a good reference that could take me through the ...
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Comparing Power of SRS to Block Randomization
I am trying to figure out how to run/analyze a block randomized experiment in the following situation, and to figure out how much of an improvement I would get over simple random sampling:
Suppose I ...
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537 views
Sample size calculation for Cluster randomized trial
In the following Paper by Clare Rutterford, Andrew Copas and Sandra Eldridge, the following formula is given for sample size calculation:
assuming the following properties:
• m - number of clusters
...
