Tagged Questions

Experimental design, or design of experiments (DOE), is the design of any information-gathering exercises where variation is present. In statistics, controlled experiments are usually implied, which involve an "experimental group" and a "control group". In the design of experiments, the ...

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Why does aov consider a 3x3 factorial design unbalanced?

I have a two factor, bot at 3 levels with all factor levels, and with 5 replicates for each. This is a standard 3^2 factorial design, and yet aov gives the message "Estimated effects may be ...
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41 views

Intuition for what happens to the standard deviation after plugging a normal variable into a function

Let's say I have a normal variable $X$. I feed $X$ into some function, which applies varies mathematical operations to it - for instance, addition, subtraction, multiplication, division, $x^r$, $e^x$, ...
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Balance checking in randomized controlled trials with large sample

I have a survey experiment in which the treated group receives a certain prompt that the control group does not. I also have a bunch of demographic variables that I want to check for balance between ...
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Explain fractional factorial design in plain English

I want to begin learning about factorial experiments and, specially, fractional factorial design. What would be a simple, plain English explanation, to get the big picture of this topic? Besides, an ...
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1answer
27 views

Experimental Design questions

I have a couple of questions regarding the procedures in an experiment. If I would like to test out two different drugs and the effect it has on the subject, why would it be a good idea to randomize ...
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How can I tell my data is a nested two-stage design?

I currently have data that looks like: ...
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1answer
245 views

What is the difference between controlling for a variable in a regression model vs. controlling for a variable in your study design?

I imagine that controlling for a variable in your study design is more effective at reducing error than controlling for it post-hoc in your regression model. Would someone mind explaining formally ...
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19 views

How Can I Build A Regression Model With Collinear Data?

Hello there my fellow Cross Validated members; I’m here today to brainstorm a little bit with all of you out there, to flesh out our collectively acquired data analytic skills, and to try and find new ...
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estimate missing values in unbalanced design

I want to estimate the NA values of the table. ...
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14 views

Use of Chi2 goodness of fit test with three-level nominal variables from two samples

I have two samples. One is comprised of people who did a pre-test but did not do a post-test (n=75). The other is comprised of people who did both the pre- and post-test (n=150). For each sample, I ...
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9 views

Selecting the right DV in study of treatment effect on a small sample?

I want to run a simple experiment at work to see if making a single change F on a product, has any significant adverse effect on the performance. I need help to ...
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1answer
32 views

Some questions about AlgDesign for Fractional Factorial Design in R

I have a few Design of Experiment type questions about the AlgDesign package in R that I can't find answered online: Will using the center=TRUE option in the ...
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38 views

Advice on research study

I am collecting data on extroversion using a personality scale at a clinic. I have about 50 subjects where 15 are in experimental group receiving interventions. I am also collecting data on ...
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15 views

What is the design of this experiment and what tests are appropriate?

My experiment has the response variable F the experimental unit is a cage the Treatment is rear (1/2 get standard rear & 1/2 get non-standard rear) and there are multiple measures of F over 12 ...
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Conditions on ratio of $\frac{\sigma_{BIB}^2}{\sigma_{RB}^2}$

I'm attempting to solve a question about the variances of random block design versus balanced incomplete block design. I feel I am close to having an answer, but I'm not quite there yet. Question: ...
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1answer
44 views

Standardized regression coefficients

I have a question regarding standardized regression coefficients and the correlation matrix. I have a two part problem that I am working on, and I need to show that the correlation matrix R is equal ...
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1answer
51 views

What is the correct model for this experiment design?

I have to analyse the results of an experiment, say, a dependent variable Y, in relation to the different treatments applied. However, I am not sure about the model to use with this experimental ...
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1answer
50 views

Minimax space-filling design for 2 dimensions in practice

I think I understand the basic idea of a 2d minimax design. Given $n$ data points, choose locations for each point so that the maximum distance between anywhere in the input space and any of the $n$ ...
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57 views

Show alias coefficient of Plackett Burman design equals $r_{ij}=\frac{c_{1i}'c_{2j}}{N}$

Consider a Plackett Burman design with N rows and let $\beta_{1}$ be the of the regression coefficients corresponding to the main effects and let $\beta_{2}$ be the vector of the regression coefficients ...
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What books to read for Biostatistician position supporting product develpment for in -vitro diagnostics?

This is not a question concerning a specific statistical method, but I need an advice. I am interested in a position as a biostatistician to support product development for in-vitro diagnostics. I ...
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35 views

How to calculate sample size for poll / ranking

Let's suppose there are Y options to choose from. I'd like to run an experiment with a sample of n participants (from a larger population), each will choose 1 option from the Y alternative according ...
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33 views

4-way Repeated Measures ANOVA

exchangers! I am struggling with my data analysis for an article I'm writing. I have to following experimental set-up. Instruction (A/B) Group (Alcohol Dependent / healthy Control) - between ...
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Selecting control locations for tiered groups?

I have groups of locations categorized by their sales performance and weekly variability into four tiers. We are running on-site tests for 100 locations in Tier A against a set of 50 control locations ...
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21 views

Multilevel propensity score

I'm trying to analyze many treatments on outcome after propensity score 1:1 matching. My problem: I have 6 differents drugs and each patient can take or not each of these. If I build my propensity ...
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1answer
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Moderated regression in repeated measures

I recently conducted a study with 4 within-subject conditions, divided over two sessions. My independent variable is degree of emotional eating (as measured by food intake after a negative mood ...
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29 views

Sample size and power calculation

I am looking for an advice on sample size and power calculation for an intervention study. The study uses a stepped wedged design. The study aims to evaluate the effectiveness of case managers ...
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82 views

Model selection using an artificially insignificant covariate

This is continued from my other post on model selection. Let me provide more details first. 1) I have a factorial design. Factor A has 5 levels, B has 2 levels, C has 2 levels. Let us assume that ...
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1answer
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Is Hurlbert 1984 the best introductory overview to pseudoreplication?

I often find myself explaining (or wanting to explain but not wanting to be boorish) the basics of random sampling and the consequences of pseudoreplication, specifically the limitations and ...
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69 views

Stratified or multi-stage sampling?

I just started volunteering with a small organization that wants to estimate the average and total number environmental trouble spots in a large US city. They have a clear definition of an ...
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1answer
19 views

Augmenting PB Design to Full Factorial

I’m planning to augment PB design to full factorial. But not able to understand statistically am I correct or not? Let me explain with example. Initially I had 11 factors & conduct PB using 12 ...
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$2^3$ Factorial Design conducted in a Latin Square Design

When does the situation occur to conduct a $2^3$ Factorial Design in a Latin Square Design? What would be the procedure of analyzing data of a $2^3$ Factorial Design conducted in a Latin Square ...
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1answer
59 views

Design of Experiments

Suppose a dermatologist wants to study the effectiveness of two different preparations of a skin lotion using two different forms of application, such as one versus two applications per day. She has ...
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30 views

A full-factorial experiment showed an interaction is significant - how do I use that?

I ran an experiment with a full factorial design. It showed that Factors A and B and the interaction ...
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1answer
58 views

Random and Fixed effect model

Would you explain a practical situation where random effect model is more appropriate than the fixed effect model?
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14 views

Data capture in psychological treatments - nonmandatory random repeat questions

this is a query for approaching a prospective exploratory study in psychological treatments It is not very easy to monitor response to psychological interventions. Usually there are standardized ...
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0answers
18 views

Fractional Factorial Design with Highest Resolution

In the book Design and Analysis of Experiments by Douglas C. Montgomery , it is written that We usually like to employ fractional designs that have the ...
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2answers
30 views

How to select a control / comparison group?

Lets say I'm creating a study that looked at treatments for metastasis in African American colon cancer patients. Would my control group or comparison group be Caucasian colon cancer patients with ...
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1answer
40 views

Fractional Factorial Design

In a $2^5$ design, it is believed that only the main effects $(A,B,C,D, E)$ and $AB,AC$ interaction effects are non-zero. I need to construct a fractional factorial with minimum number of runs which ...
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1answer
31 views

$2^{5-2}$ Design : Alias Structure

$2^{5-2}$ Design Design Generators: $D=AB\quad E=AC$ Defining Relation: $I=ABD=ACE=BCDE$ $$\text{Aliases}$$ $$A=BD=CE=ABDE$$ $$B=AD=ABCE=CDE$$ $$C=ABCD=AE=BDE$$ $$D=AB=ACDE=BCE$$ ...
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31 views

How should I design an experiment with non-binary factors?

We are preparing an experiment that will run during the coming winter, where we assess certain energy performance indicators on a set of single-family houses in Europe. We are interested in finding ...
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1answer
61 views

Why people often optimize the determinant of $(X'\Sigma X)^{-1}$

Say I have a random vector $Y\sim N(X\beta,\Sigma)$ and $\Sigma\neq\sigma^2 I$. That is, the elements of $Y$ (given $X\beta$) are correlated. The natural estimator of $\beta$ is ...
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1answer
24 views

Experimental design considerations for Randomized Block design

Is there a use of using a Randomized Block design when you only have one treatment and you only want to test the effects of this single treatment? The experiment in question is to see whether a ...
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1answer
40 views

Extremely new to R: Support.CEs package - help with design matrix please!

I've only started using R one day ago, still so much to get my head around. I need to create a choice experiment, and I have been following the example of H.Aizaki I think I have created a successful ...
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1answer
57 views

Random Effect Model

One factor random effect model: $$y_{ij}=\mu+\tau_{i}+\epsilon_{ij}\quad i=1,2,\ldots,a; j=1,2,\ldots,n$$ where, $y_{ij}$ is the $j$th observation of $i$th treatment effect $\mu$ is the overall ...
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41 views

Computing the F-ratio under null hypothesis

Statistical model for a Completely Randomized Design: $$y_{ij}=\mu+\tau_{i}+\epsilon_{ij}\quad i=1,2,\ldots,a; j=1,2,\ldots,n$$ where, $y_{ij}$ is the $j$th observation of $i$th treatment effect ...
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1answer
37 views

Which design is most appropriate?

I have data from an experiment testing a new treatment. Each subject has 4 data points, 2 of the new treatment and 2 of the control. It is like a paired analysis, but instead having 1 observation of ...
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143 views

logistic regression with dummy variables for fractional factorial design

We have conducted a survey experiment with varying amounts of incentive (factor 1 = I1, I2, I3, I4, I5). The experiment was conducted stepwise in three subsequent studies (factor 2 = S1, S2, S3). ...
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1answer
70 views

Is there an equivalent to LHS for a discrete input space?

I was wondering if there is a method that is equivalent to Latin Hypercube Sampling when the input space you are trying to sample from are a finite discrete set of possible values. For example, if I ...
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1answer
53 views

Identifying the experimental unit

I have included a diagram of an experiment where cells are pooled from multiple animals, cells from the pool are then allocated to different treatments and a measurement is taken from each individual ...
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50 views

Correct use of Mixed model for random block design?

I have the following experimental design (random block design). Block with 4 Treatments (A, B, C, D) repeated at 4 different sites. Treatments were applied to individuals of different species (factor ...