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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What's the magic of randomization? [closed]

I've read that one can perform A/B tests & effect size inference given that a population was randomly sampled and allocated to A & B groups. You simply give the treatment to group B and the ...
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Causal diagrams necessary in randomized controlled trials?

I understand how a properly administered RCT rules out confounders because there are no variables influencing the treatment/control group assignment except randomization (meaning no backdoor paths ...
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Estimating Complier Average Causal Effect (CACE) in a Field Experiment with One-Sided Noncompliance

I am working on a referee report for a field experiment focused on the employment process. The experiment investigates if including a video in job applications can reduce employment disadvantages for ...
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Can we perform a MANCOVA for paired data?

I have data for a cross-over randomized controlled trial. I wonder if I can use MANCOVA to compare my outcomes (they are continuous) while having paired data. If I can't, what would be an appropriate ...
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How should I analyse this experiment with two blocking factors

In this experiment, a machine is used to compare the wear resistance of 4 different types of rubber-coated fabric (variable mat coded A, B, C and D). To do this, ...
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What is a Randomized Complete Block Design. How do we create one and analyze it?

I have been reading about experimental design, and Randomized Complete Block designs (RCBD) in particular and I have a few queries. What exactly is a randomized complete block design ? Is there a ...
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Design of experiment in multiple regression

Suppose we have the following model of our environment: $\hat{y}_t = e^{dayofweekeffect} * x_{1, t}^{\beta_0} * x_{2, t}^{\beta_1}$ which we can linearize into: $log(\hat{y}_t)= dayofweekeffect + \...
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Instrument variable analysis using randomized data

I am analyzing the effect of two randomized interventions on 1) first-time and, 2) second-time event attendance. All variables are binary (0 vs. 1). Second attendance was conditional on first ...
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Sample size calculation for a three independent arm RCT with a categorical outcome

I have three study arms on interventions A, B, and C, which are independent of each other. The primary outcome is categorical (positive or negative). The null hypothesis is A = B = C. From prior ...
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Does my study design have randomization issues?

I am helping to design a study where participants will be randomized to one of three arms -- a control arm, treatment 1 or treatment 2. Within each arm, they will then also receive either no ...
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No more than $n$ moose, but how many?

Introduction I am thinking about how to estimate the number of individual moose from wildlife camera photos. I have the latitude and longitude position of each observation, along with a datetime of ...
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Time clusters in a randomised trial

In cluster randomised trials, some clusters are treated whereas others are not. Usually, the clusters are geographical unit, e.g. villages. However, am I right that, in principle, the clusters could ...
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Ran out of envelopes in randomized control trial

We are conducting a randomized control trial (RCT) comparing treatment vs. control from 4 sites (A-D). We have planned for 100 patients from each site. 100 envelopes of treatment assignment (...
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Do I understand correctly how a split system should work in AB tests

I have a question about how a split system should work. I have a product. Which looks like eBay. We conducted an experiment that should increase the number of users who choose one of the categories. ...
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Randomization of questions in an online survey

I want to run an online survey about people's preferences for environmental policies in different economic sectors using a Likert-type scale (strongly disagree, disagree, etc.). I have 4 sectors and 4 ...
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Choosing the best and more useful method in RCT psychology studies

I'm not sure had anyone open this question but I'd like to your opinions. When we compare two groups(control&treatment) measured at pre,post and a follow up procedure, which is the most useful ...
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Which is the correct way to deal with insignificant main effect of Group condition? Stick with interaction effect in RM-Anova or perform ANCOVA?

I wanted to ask conceptual about what to do with main effects? Assume, I have randomly assigned equal two groups(let's say CBT, Control; N1=25; N2:25). I collected the depression levels at three time ...
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Optimizing Treatment Group Assignments

When setting out experiments, I want to make sure treatment groups are as balanced as possible. Instead of using randomization, I've started to use the following process. I first collect some ...
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Why is covariate balance fundamental for causal inference in observational data but unnecessary in experimental data?

The observational case For observational data, Hernán & Robins (2023, p. 49) state: In the absence of marginal randomization, [computing the average causal effect in the entire population] ...
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Causal identification when some ITEs are 0

Say I have some data from an RCT related to a skills training program. The data are such that: Marginally randomized binary treatment z. Those with ...
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Why is the Central Limit applicable in A/B testing?

I am having trouble understanding why the Central Limit Theorem (CLT) is applicable in A/B testing. As a beginner in statistics, I am trying to grasp the intuition behind it. The CLT states that as we ...
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The proof of the Euler method decomposition of VaR

For a portfolio-wide profit/loss variable $X= \sum_{i=1}^{n}w_iX_i$ the value-at-risk of $X$ at confidence level $\alpha$ (usually close to 1) is defined as the $\alpha$-quantile of $-X$: \begin{...
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Can we do some causal conclusions if the mediator follows the dependent variable?

We have a survey consisting of two waves ($N=4000$). In Wave 1, we ask block of questions $M_1$. In Wave 2, we ask blocks of questions $W$, $Y$, $M_2$ The order of questions is as follows: $W \...
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Understanding the advantages of CRD experiments

I am self studying an introductory course on Designed Experiments and have come across the notion of a Completely Randomised Design (CRD) defined as follows: Completely Randomised Design: the ...
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How much of a discrepency is tolerable if Sample Ratio Mismatch is detected?

We have analyzed several past online A/B tests and revealed that some of them have SRM at a statistically significant level (p<0.001). Example: we had 50%/50% traffic allocation between control and ...
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Is a high prediction performance of allocated treatment evidence for lack of unobserved confounding?

Example Say Investigator 1 is looking to investigate the effect of fish consumption (a binary variable $A$ indicating whether they eat or do not eat fish) on cardiovascular health (a continuous ...
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What’s a good scale robust similarity metric?

Context: While designing an experiment, there is interest from leadership in pairing control and test units together such that every (test, control) pair are as categorically similar as possible. ...
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Why training is smoother when no randomization of batch after each epochs is applied?

I am wondering why training error converges more smoothly when I am not applying randomization after each epochs? After each epoch I am taking the loss obtained in my last minibatch. I see that when ...
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Equal size random assignment

I am doing a ab test. I want to test if a treatment is statistically better than a control. I want to split 30 subjects randomly and evenly into two groups. My way is first generate random number for ...
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Balanced incomplete block design - randomizing treatment order

In a balanced incomplete block (BIB) design, what is the best way to ensure each treatment appears in all positions/orders? Should I randomize treatment order within each block, so that participants ...
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Medical experimental design with non-comparable control

My population consists of people at high risk of cardiovascular disease who are identified through standard blood tests. These people, when identified, are prescribed some standard medication. I will ...
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Help Needed for Outliers detection post paired T-test statistical test

I don't know if this is a standard way od doing things so open to any suggestions, basically I have done random sampling from my population to create 2 groups Treatment & Control. I also have few ...
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What statistical design and analysis is appropriate for this single-arm study?

I have research to perform but I am not very familiar with statistical design and the relevant analysis that I have to do, but here is the idea of what I want to do: It is a single-arm study, I have a ...
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Switching interventions after randomization

Suppose in a randomized control study, we assigned each individual to one of two interventions (A or B) with equal probability. And suppose for the sake of argument, there is complete balance in ...
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Test statistics for randomization

I have a basic question on what method should be applied to obtain test statistics distribution. I have two treatments $A$ and $B$. I want to test on mean $H_0: \overline{t}_A=\overline{t}_B$ as ...
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Bootstrapping confidence intervals in randomization model and population model

Ernst 2004 shows that the permutation tests in the random assignment scheme (e.g., controlled experiment) and in the random sampling scheme (e.g., observational study) share the same constructing ...
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In a randomized trial, should we exclude random intercepts and use only slopes?

Let's say I have a longitudinal study, with patients assessed at several time points, which goal is to compare the treatment vs. placebo. If, theoretically, I used a mixed model to analyse the ...
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AB Test, Experimental Design based on Machine Learning Output

Looking for the best way to set up an AB test. Scenario is that the online product I am working with has logged in users that pay a monthly fee, and they can upgrade to get access to more features. ...
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Balance checking (using discrete variables)

Context I'm doing a field intervention, with 4 treatments and 1 control. I have done a stratified randomization beforehand to ensure that demographic characteristics (gender, age, income group) are ...
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RCT using simple Randomisation, can extra participants be added?

I have been asked to perform the randomisation for a small RCT using simple randomisation. There are 100 individuals to randomise to one of two arms (control vs intervention). The researchers have not ...
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Inference for the average treatment effect for Bernoulli trial

In the book of Imbens and Rubin, they discuss four common classes of assignment mechanisms that fit into this framework: Bernoulli trials, completely randomized experiments, stratified randomized ...
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Are the arguments that placebo can be unethical mistaken?

There seem to be two ideas of placebo - or the treatment received by a placebo group: A "simulation" of a treatment using saline or sugar pill so that subjects in a clinical trial can be ...
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preference between completely randomized or stratified/paired randomized design under covariate not predicting outcomes?

Consider potential outcome of $i-$th unit $Y_i=(Y_i(0),Y_i(1))$ with $0$ as control and $1$ as treatment and say $X_i$ is the only covariate associated to $i-$th unit. Assume $X_i$ does not predict $...
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Comparing treatments when there is imperfect compliance

Imagine a situation where we have a 2x2 cross-randomized program with imperfect compliance to the treatment arms. Thus, units are assigned to treatment A, treatment B, or both treatments. Once they ...
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How to forecast a rental weekly sales demand using a 4 year history data?

I need to estimate the weekly demand required for a specific product in a specific week at a specific location. I have the past 4 years daily data of each product at each location. For example: number ...
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Which test(s) should I use for RCT, 2 groups (intervention vs. comparator) and two DVs measured at multiple points (pre, post, 3, 6, 12 months)?

I am planning an RCT to evaluate the short- and long-term effectiveness of a CBT intervention. There will be two groups: intervention vs. active comparator and two outcome measures: anxiety scale and ...
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Entropy balancing what are the gains in applying the technique?

I am developing a research that involves a model and when estimating it the coefficients were not significant. Because the hypotheses are strong, my advisor suspects that there is some problem in the ...
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My random allocation schedule list ran out - is it valid from a statistical standpoint to simply generate a new list?

Problem My random allocation schedule list was design to randomize 100 participants. 50 participants have been recruited so far and randomized to treatment A or B. A recent change to the assumptions ...
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Current examples where randomized studies yield different results than observational studies

I have been reading the following paper by G. Smith (2002). I found it rather surprising. Some excerpts: Promising epidemiological and laboratory findings led to a paper published in 1981 in Nature ...
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Excluding participants due to issue in randomisation?

I have been carrying a study and due to a human error in the randomisation process, instead of getting equal sized groups (I have 8 and aimed to have 100 per group), I now have around 90-100 ...
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