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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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Experiment design to determine effect of ads on etsy shop performance

I am looking to design an experiment to determine the impact of turning on etsy ads for my shop. I opened a shop for plant pots and have made 27 sales in the 4 months I have been open. I am ...
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2 votes
1 answer
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Longitudinal analysis of peer effect

I am working with hierarchical data (2 repeated observations on children nested within households), obtained from a RCT with 2 treatment groups. The primary goal of my analysis is to see whether the ...
Shen Shen's user avatar
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a few questions on stratified analysis

If one of the 3 stratification factor from IWRS has data errors, should we replace it with CRF collected baseline values? Will this break the balance of the strata blocks? For non ITT population, say,...
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Power estimate for an interaction term in factorial design

I am trying to estimate power for a factorial design (2x2). My initial approach was to estimate pair-wise minimum detectable effect sizes : i.e., if I know sample size, allocation to each group and ...
Ploit88's user avatar
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Why should you want to use a smaller control group?

In an RCT with multiple treatment arms, I heard that the "pure" control group be small to if we expect the effect size to be large. Why would this be the case? I understand that we could ...
Ploit88's user avatar
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3 votes
2 answers
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Analyzing an experiment which consists of many "small" experiments

Consider the following setting: I am trying to choose between two bakers for my new bakery, Baker A and Baker B. The way that I am evaluating them is on a set of different cakes on the menu: Cake 1, ...
gaussiandynamics's user avatar
3 votes
1 answer
146 views

When and how of stratification?

I understand stratification at a novice level. For example, if we want to condition on gender in post experimentation inference, we might stratify or block on gender. As I understand it, we take each ...
jbuddy_13's user avatar
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Random permuted block sizes in a randomised clinical trial

What is the best way to choose the block sizes in a randomised clinical trial? Randomisation for an ongoing trial is stratified by site (2 sites) and gender (m/f) for 4 strata - it uses random ...
Megan Moreton's user avatar
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3 answers
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Sample size calculation for a multicenter RCT

I'm very new to the world of statistics, so sorry in advance for my limited knowledge. I hope you don't mind helping me. We are currently setting up a multicenter RCT of treatment A versus placebo in ...
Catherina Muscat's user avatar
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1 answer
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High power in A/A test, interpretation?

Randomization has already been executed and two groups have already been assigned, where treatment observations and control observations are captured by df1, df2 respectively. Note: Treatment exposure ...
jbuddy_13's user avatar
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Show conditional independence in randomized experiment

I'm new to causal inference, and I have a question regarding a potential causal relationship. I'm wondering if the following assumption holds: $(Y_i(1), Y_i(0), X_i) ⊥ Z_i -> (Y_i(1), Y_i(0)) ⊥ Z_i ...
user408381's user avatar
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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 ...
jbuddy_13's user avatar
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18 votes
3 answers
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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 ...
john_hawthorne's user avatar
1 vote
1 answer
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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 ...
yusefsoliman's user avatar
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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, ...
Vivek Sharma's user avatar
3 votes
1 answer
290 views

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 ...
Vivek Sharma's user avatar
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1 answer
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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 + \...
hugh's user avatar
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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 ...
llsabang's user avatar
2 votes
1 answer
132 views

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 ...
Bradex's user avatar
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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 ...
Jay Bee's user avatar
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1 answer
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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 ...
Galen's user avatar
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3 votes
2 answers
81 views

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 ...
afreelunch's user avatar
6 votes
1 answer
68 views

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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1 vote
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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. ...
Roman Stasiuk's user avatar
1 vote
1 answer
101 views

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 ...
olbap79's user avatar
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1 answer
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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 ...
Connor's user avatar
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3 votes
1 answer
47 views

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 ...
David Moore's user avatar
3 votes
1 answer
317 views

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] ...
Kuku's user avatar
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1 vote
0 answers
22 views

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 ...
lex's user avatar
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7 votes
4 answers
1k views

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 ...
Nab's user avatar
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1 vote
1 answer
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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 ...
FD_bfa's user avatar
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1 answer
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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 ...
Gustavjung's user avatar
1 vote
0 answers
15 views

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 ...
Kuku's user avatar
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0 votes
0 answers
26 views

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. ...
jbuddy_13's user avatar
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1 vote
0 answers
17 views

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 ...
yoshcn's user avatar
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1 vote
1 answer
263 views

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 ...
Guanyan Lin's user avatar
0 votes
1 answer
67 views

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 ...
Dani's user avatar
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3 votes
1 answer
117 views

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 ...
user2974951's user avatar
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0 votes
0 answers
69 views

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 ...
av abhishiek's user avatar
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0 answers
30 views

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 ...
Aura's user avatar
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5 votes
2 answers
300 views

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 ...
Tom Chen's user avatar
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1 vote
0 answers
71 views

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 ...
user45765's user avatar
  • 1,445
2 votes
1 answer
93 views

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 ...
panda's user avatar
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2 votes
1 answer
591 views

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 ...
Re-searcher's user avatar
1 vote
1 answer
44 views

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. ...
abtesting's user avatar
0 votes
1 answer
59 views

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 ...
lionclw's user avatar
  • 55
2 votes
1 answer
95 views

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 ...
ReadBeard's user avatar
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1 vote
0 answers
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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 ...
TrungDung's user avatar
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6 votes
1 answer
121 views

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 ...
AdamO's user avatar
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