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.

Filter by
Sorted by
Tagged with
9
votes
1answer
12k views

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 ...
8
votes
1answer
2k views

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 ...
6
votes
2answers
6k views

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 ...
6
votes
1answer
2k views

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. ...
5
votes
1answer
6k views

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 ...
5
votes
1answer
95 views

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) ...
4
votes
2answers
7k views

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 ...
4
votes
1answer
135 views

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 ...
4
votes
2answers
733 views

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 ...
4
votes
1answer
45 views

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 ...
3
votes
1answer
44 views

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 ...
3
votes
1answer
41 views

Is there an experimental design that tests three different factors?

I am planning on performing data collection on subjects to see how well certain wearable products perform. Let's call the products A, B, and C. The goal is to see if any of the products performs more ...
3
votes
1answer
139 views

Is it appropriate to consider the interactions between blocking and fixed factors

If you have an experiment with multiple treatments (lets say 4 fixed factors with varying levels each) and you use a randomized complete block design, is it appropriate to consider the interactions ...
3
votes
1answer
193 views

Experimental design vs factorial design

During my study about experimental design, I detect from some examples that factorial design is a sub-step in an experimental design. However till now the idea seems not fully clear for me. What is ...
3
votes
1answer
3k views

Randomized Complete Block Design: what if the block random factor is significant?

I'm conducting a two-way analysis of variance. I have one fixed treatment factor and one random block factor and I have $n=1$ for any combination. The thing is that the random block factor is ...
3
votes
1answer
499 views

Examples of connected designs in DOE

I want to understand connectedness in block designs , I know this about connectedness : a design is said to be disconnected if we are able to create two separate groups such that they do not contain ...
3
votes
1answer
417 views

Using blocking in propensity score analysis?

I'm considering blocking my analysis dataset on one or two key variables prior to a standard sub-classification propensity score analysis. For example, if my dataset (which contains member level pre- ...
3
votes
2answers
1k views

Balanced Incomplete Block Design (BIBD)

If treatment $1$ appears in $r$ blocks and there are $(k-1)$ other treatments in each of those blocks, there are $r(k-1)$ observations in a block containing treatment $1$. But the following Table ...
3
votes
1answer
1k views

Incomplete block design analysis / design with R

I have a few questions that arose when working on designing the following experiment. The numbers and variable levels are all made up for examples sake. I want to test the effect of incubation period ...
3
votes
0answers
50 views

How to analyze data with a lot of missing data (including covariate, nesting and blocking)

I have data set that was haphazardly collected to test grazing impact on soil. To test the grazing impact, 6 replicate soil samples were collected from inside a fence and 6 replicates were from ...
2
votes
2answers
1k views

Is there a non-parametric test, like a Kruskal-Wallis, but with uneven blocks?

I have a continuous response variable, nominal independent, and want to block by site, though the numbers at sites are unequal. Is there any alternative to a permutation test? If not, does anyone know ...
2
votes
2answers
3k views

How can I block by location in R?

Still new and learning how to use R, but I'd like to get some help with figuring out how to block my data by location. I found this tutorial, but I don't understand where to put my data into the code. ...
2
votes
1answer
335 views

Balanced incomplete block design

In a BIBD, let $a$ denote the number of treatments; $b$ denote the number of blocks; $k$ denote the number of treatments exactly in each block; $\lambda$ is the number of times each pair of ...
2
votes
1answer
516 views

Insignificant block effect in two-way block design

I used a two-way ANOVA to analyze data collected in a randomized complete block design: Y~Treatment+Block, where blocks represented spatial units Whereas Treatment had a significant effect on Y, ...
2
votes
1answer
13 views

which experimental design better fits?

I test the effect of a plant dose on the abundance of a specific microbe, cultured in glass tube in vitro. The treatment consist of 5 doses (0, 1, 2, 3, 4). Each culture tube receives one of the dose ...
2
votes
0answers
48 views

standardising independent and dependent variables within blocks?

I have data from a randomised blocked experiment testing the effect of different crops on weeds. Each treatment was replicated in one plot in each of three blocks, on two farms, in two years (but NOT ...
2
votes
0answers
42 views

What makes a block a block

In multivariate analysis involve analysing different data sets of the same individuals, sometimes it is called integration or multi-block analysis. However I can't find how are these dataset defined: ...
2
votes
1answer
107 views

How Is This Design a Randomized Complete Block Design?

I recently started learning about one-way ANOVA, multiple comparisons, and contrasts. At the moment, I have an introductory-level knowledge of these concepts. I'm analysing an experiment that ...
2
votes
0answers
61 views

I think this is a RCB design…but I'm not sure how to analyze it

Edit: Clarified by including the overall question I need help with and the experimental questions of my project. Overall question to you (ie, what I need help with): Does this experiment sound like a ...
2
votes
0answers
499 views

Repeated measures on split plot design with blocking

This is the first time I'm posting a question here. I have regularly been using the questions and answers here as example solutions for my problems, and searching has always helped me figure things ...
2
votes
1answer
90 views

Blocking effect in Experiment

Let $T\in\{0,1\}$ be the variable representing the treatment. Let $X\in\{0,1\}$ be the variable representing the attributes of subject. For example, $T$ is a new medicine that will make people grow ...
2
votes
0answers
253 views

adonis in vegan: limiting permutations when design isn't fully blocked

I have read over the help files and examples online on using adonis with blocked designs but haven't really found a solution to my particular case. I'm fairly new to permutation-based methods so ...
2
votes
0answers
63 views

Syntax for unbalanced block design with nesting

I am trying to run a model in which I have site as a blocking factor, and two layers of nested random effects due to sub-sampling. The nesting layers are-> plant[flower[robbing status]]. My response ...
2
votes
0answers
420 views

Non-Randomized Block Design?

Suppose I am running a $2^2$ factorial design in two blocks. Denote the factors as A and B and the four treatment combinations as $(1), a, b$ and $ab$. Consider the blocking arrangement: ...
2
votes
0answers
686 views

BIBD or IBD or PBIBD

I use block design for discrete choice experiment. While Balanced incomplete block design(BIBD) is considered as gold standard for blocking in choice experiments. However this is not always possible ...
1
vote
2answers
2k views

How to generate a Randomized Complete Block Design?

I'm studying agriculture and I'm looking for answers concerning one of my problem. I have to implement a randomized complete block design and I would like to generate it with R. I've found some ...
1
vote
1answer
224 views

Is this a Blocked design ANOVA, two way anova, or ANCOVA

I am running ANOVA to test for a significant effect for some data, and a grad student said I should run an ANOVA test formatted like this in R to test for significance: ...
1
vote
1answer
69 views

Incomplete block design analysis

I have 4 treatments (6m, 12m, 24m, 40m) in 3 blocks, but all treatments are not replicated in these blocks: 6m, 12m, 24m are in Blk1 and Blk2 and Blk3 consist of only 34m (control plot) and 6m. How ...
1
vote
1answer
84 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 ...
1
vote
1answer
108 views

Random block mixed ANOVA

We tested proliferation of 4 types of cells (between-subject factor) during 3 consequent time points (within-subject factor). All test were done in 4 blocks with 1 plate of each type of cells in each ...
1
vote
1answer
1k views

Is Randomized Complete Block Design a two-way anova?

Isn't Randomized Complete Block Design a two-way anova ? Can it be one-way ? As far i understand, since there is treatment effect and also block effect in RCBD, it is two-way anova. But can it be ...
1
vote
1answer
3k views

Linear mixed effect model with repeated measures using lmer

Background I think I am close to the error structure I want for random effects but not sure about some parts of it. I am carrying an experiment on wheat plots in a field to measure the increase in ...
1
vote
1answer
455 views

Unequal variance, one replication, empty cells RCBD ANOVA

I could use some advice on how to handle this situation. I have a Randomized Complete Block Design (RCBD) ANOVA with 5 blocks and 8 treatments, the response is dry weight of some plant, there is 1 ...
1
vote
1answer
30 views

Blocking vs. Control

Am I thinking about this correctly? Blocking is something that is done on the experimental design level: If I'm not interested in the differences between school districts, I block by school district ...
1
vote
0answers
38 views

Why is ABC interaction completely confounded in this factorial experiment?

Consider a 2^3 factorial design layed out in 2 blocks ,with plot size 4, as follows Block I: {1,ab,ac,bc} Block II: {a,b,c,abc} This is replicated four times. abc is said to be completely ...
1
vote
0answers
58 views

Randomized Block Design Models

I have been asked to fit the following models in R: The models are based on this data: I know the mediums are the blocks and the units of the active ingredient are the treatments. I understand how ...
1
vote
0answers
10 views

Test for yield and disease incidence in block design

I need to analyse a set of data coming from an agricultural experiment, with the intention of assessing the incidence of a certain disease in potatoes under three different treatments (plus blank). I'...
1
vote
0answers
19 views

Randomized blocking “after the fact”

I have 5 treatments that I'm going to randomly assign to visitors to my website. I'll have 10,000 or more visitors. Is it statistically valid to analyze the results based on visitor characteristics ...
1
vote
0answers
108 views

Specifying ANOVA with incomplete block design (R)

I have experimental data of individual sizes (continuous) as a function of two categorical variables (A and B) each with 2 levels (1 and 2), along with a control treatment. Each treatment condition ...
1
vote
0answers
70 views

Coefficients in a Randomized Block Design

If, for example, I am running a GLM with Poisson distribution (it could be any distribution) and I have a Randomized Block Design (RBD) [Note: I dont wanna run a GLMM just to put the blocks as a ...