I'm looking at Latin Squares. I've seen standard Latin squares, and Latin squares when the rows are randomised, then columns are randomised.
When would one be used over the other?
It seems as though the randomised would always be better as the ordering of the rows is less consistent. For example, in a 5x5 Latin square the pattern D,E would appear in the rows 4 times. I'm not sure how to justify that though, or if it is even true.
edit - standard and randomised Latin square, experiment
Often there is initially a standard cyclic square as follows :
Experiment :
------------
Di = ith Driver
Cj = jth Car
A,B,C,D = different tyres
reponse = fuel efficiency
------------
standard latin square
[C1] [C2] [C3] [C4]
[D1] "A" "B" "C" "D"
[D2] "B" "C" "D" "A"
[D3] "C" "D" "A" "B"
[D4] "D" "A" "B" "C"
The rows and columns of this can be randomised to give
randomised latin square
[C1] [C2] [C3] [C4]
[D1] "D" "B" "A" "C"
[D2] "C" "A" "D" "B"
[D3] "A" "C" "B" "D"
[D4] "B" "D" "C" "A"
edit 2 - experiment across different days with the same Latin square
In this approach the experiments have the same tyres for each row and column
Experiment :
------------
Di = ith Driver
Cj = jth Car
A,B,C,D = different tyres
reponse = fuel efficiency
------------
Day 1
[C1] [C2] [C3] [C4]
[D1] "D" "B" "A" "C"
[D2] "C" "A" "D" "B"
[D3] "A" "C" "B" "D"
[D4] "B" "D" "C" "A"
Day 2
[C1] [C2] [C3] [C4]
[D1] "D" "B" "A" "C"
[D2] "C" "A" "D" "B"
[D3] "A" "C" "B" "D"
[D4] "B" "D" "C" "A"
edit 3 - experiment across different days with different same Latin squares
Here there are two different squares, but note that (D1, C2) is the same for each of them.
Day 1
[C1] [C2] [C3] [C4]
[D1] "A" "B" "C" "D"
[D2] "B" "C" "D" "A"
[D3] "C" "D" "A" "B"
[D4] "D" "A" "B" "C"
Day 2
[C1] [C2] [C3] [C4]
[D1] "D" "B" "A" "C"
[D2] "C" "A" "D" "B"
[D3] "A" "C" "B" "D"
[D4] "B" "D" "C" "A"
edit 4 - experiment across different days, ensuring that the same tyre isn't used in the same row/column position across days
Here the standard square has been used as a base.
In order to remove bias between days the rows have been shifted, so
row 1 sent to row 4
row 2 sent to row 1
row 3 sent to row 2
row 4 sent to row 4
Here is the latin square experiment. Latin square to reduce bias within the square, and altered rows to reduce bias between the experiments
Day 1
[C1] [C2] [C3] [C4]
[D1] "A" "B" "C" "D"
[D2] "B" "C" "D" "A"
[D3] "C" "D" "A" "B"
[D4] "D" "A" "B" "C"
Day 2
[C1] [C2] [C3] [C4]
[D1] "B" "C" "D" "A"
[D2] "C" "D" "A" "B"
[D3] "D" "A" "B" "C"
[D4] "A" "B" "C" "D"
Summary
So the reason that we don't use the same square (like in edit 2) for each
day (experiment) is that there may be bias introduced from driver D1 using car
C1 with tyres B. Therefore we need to reorder the square between experiments
in a non random manner.
In edit 3 I've used the standard square and the randomised square but this isn't enough (presumably) because there are some squares which have the same tyre for each experiment. So I have made edit 4 based on the standard square, with the rows shifted between days (experiments) to ensure that the same tyre doesn't appear for the same car/driver.
