Statistical Analysis Stack Exchange
Statistical Analysis Stack Exchange

Questions tagged [blocking]

In the design of experiments, blocking refers to grouping similar experimental units together in groups ("blocks"). Comparing treatments based on within-block differences reduces the influence of extraneous variables, thus increasing power.

127 questions
23
votes
5 answers

What is a block in experimental design?

I have two questions about the notion of block in experimental design : (1) What is the difference between a block and a factor ? (2) I tried to read some books but something is not clear: it seems that the authors always assume that there is no…
Stéphane Laurent
  • 17,425
  • 5
  • 59
  • 101
10
votes
1 answer

adonis in vegan: order of variables or use of strata

I am using the adonis() function in in the vegan package to determine 1) if co-occurring host species vary in their microbial community across multiple sites, and 2) if sites are different. I have examined all posts on CV and SO, and there is no…
Carly MW
  • 111
  • 1
  • 1
  • 8
8
votes
1 answer

Why is blocking necessary in experimental design if we already perform random assignment?

I am going through the first part of the Duke statistics course on Coursera, and the concept of blocking in experimental design comes up. If I understand correctly, blocking refers to separating subjects into groups based on some variable that might…
dragonfly
  • 91
  • 1
  • 4
7
votes
1 answer

3 Treatment Agronomic Experiment: Latin Square or Randomized Complete Block Design with 4 replicates?

I need help with designing an experiment. Suppose I am testing 2 fertility programs against a control in Lettuce, for a total of 3 groups (Program A, Program B, and Untreated Control). Let's assume that the field has no noticeable differences in…
Juan
  • 71
  • 3
7
votes
0 answers

Is ANOVA always more powerful than a two-sample t-test when the data can be blocked?

I am trying to compare the efficacy of two devices. Three different operators tested each device for a parameter of interest (the same 3 operators for each device) and yielded two data sets for each device. My first thought was to perform a simple…
David Webb
  • 367
  • 1
  • 5
6
votes
1 answer

How to analyze this incomplete block design in R?

I was just wondering if you could point me in the right direction. I have a dataset with 5 tree clones planted at 10 different sites, i.e. same clones are replicated twice at different sites. Site Clone 1 A 2 A 3 B …
Stefan
  • 4,977
  • 1
  • 18
  • 38
6
votes
2 answers

Random block design ANOVA in R

Quick question: I have found this tutorial which recommends a two-factorial design for the following setup: three menu items (fixed factor) are tested in six restaurants (random factor). The guide recommends using aov( response ~ item + restaurant…
January
  • 6,999
  • 1
  • 32
  • 55
5
votes
1 answer

Crossed vs. nested & fixed vs. random factors

A barn has 4 sections of animals. Within each section are 4 goats. Each goat is given one of four types of food. One of each goat's kidneys is randomly selected to be inspected after 3 days for level of carbohydrates. To measure the level, the…
simplemts
  • 81
  • 1
  • 3
5
votes
2 answers

Can covariates be categorial variables?

I have a 2x2 experimental design. In the experiment, I also collected the participants' professional qualifications (categorical variable- yes /no). I would like to test the effect of controlling this variable on the MSE. I understand that in…
LoveExps
  • 51
  • 1
  • 2
5
votes
1 answer

Experimental Design Problem with Goofy Constraints

I am having trouble designing an experiment. I will give a hypothetical example that shares the main features of my actual problem. Suppose there are: $M$ meadows, indexed by $m={1,...,M}$, where $M \approx 1000$ if that simplifies things. $F$…
dimitriy
  • 31,081
  • 5
  • 63
  • 138
5
votes
1 answer

Do I want a mixed model for fractional factorial designs?

I have created a d-efficient fractional factorial design of 48 combinations from a total of 192 possible combinations (4x2x2x3x2x2). For the experiment, I plan to have 4 runs in 12 blocks and 40 individuals for each block completing the 4 runs. Each…
T-Porsch
  • 63
  • 7
5
votes
2 answers

Effects of blocking on type I and type II error rates

I am studying blocking in ANOVA and I am wondering about the following scenario. Suppose we did a Generalised randomised block design. Suppose SSBL = 0 and it also had not interaction effect with the treatment. Now if I do the F test on the…
Durin
  • 964
  • 2
  • 7
  • 17
5
votes
1 answer

Testing for the effect of an intervention when it is applied on a group of which each individual is measured

Suppose we have 500 students nested in 20 classes (different classrooms), 25 students per class student<-factor(1:500) class<-rep(LETTERS[1:20],each=25) They all take a test. score<-rnorm(500,mean=80,sd=5) The model below would tell you about the…
Thomas Levine
  • 3,001
  • 1
  • 16
  • 16
4
votes
2 answers

Crew selection: ranking rowers by letting them race against each other

Seat selection is a common practice in competitive rowing and I would be curious about more solid statistical underpinnings: there are more rowers in a team than the 8 seats in the crew boat. So the coach splits the team repeatedly into two smaller…
Christian Lindig
  • 203
  • 1
  • 6
4
votes
1 answer

Downsides of stratified randomization in experimental design

When sample sizes are too small to trust that the usual asymptotics will guarantee good balance across experimental groups on known confounders, a common approach is stratified or blocked randomization. What, if any, are the practical or statistical…
half-pass
  • 3,594
  • 7
  • 23
  • 34
1
2 3
…
8 9