具体的说拉丁方是一种为减少实验顺序对实验的影响，而采取的一种平衡实验顺序的技术。采用的是一种拉丁方格做辅助，拉丁方格就是由需要排序的几个变量构成的正方形矩阵。其具体的应用过程是这样的：
当处理数是偶数时，其顺序是这样确定的，横排：1，2，n，3，n-1，4，n-2……（n代表要排序的量的个数），随后的次序是在第一个次序的数目上加“1”，直到形成拉丁方。
假设处理数是6，则拉丁方如下：
A B F C E D
B C A D F E
C D B E A F
D E C F B A
E F D A C B
F A E B D C
拉丁方以表格的形式被概念化，其中行和列代表两个外部变量中的区组，然后将自变量的级别分配到表中各单元中。简单的说就是某一变量在其所处的任意行或任意列中，只出现一次。
2 Experimental Methods
•It is important to select the right experimental method so that the results of the experiment can be generalized
•There are mainly two experimental methods
•between-groups:
each subject is assigned to one experimental condition
- Each subject performs under all the different conditions
- Repeated-measure
•within-groups:
each subject performs under all
the different conditions
- Each subject is assigned to one experimental condition
| Within-subjects |
Between-subjects |
|
| Learning effect |
Avoids interference effects
(e.g. practice / learning effect) |
|
Longer time for each participant
(larger impact of fatigue and frustration) |
Shorter time for each participant
(less fatigue and frustration) |
|
| Individual difference can be isolated |
Impact of individuals difference |
|
Easier to detect difference between
conditions |
Harder to detect difference between
conditions |
|
| Requires smaller sample size |
Require larger sample size |
|
Counterbalance/randomize the order of
presenting conditions |
Randomized assignment to conditions or matched groups |
|
| |
|
|
Counterbalancing•
All possible permutations
- 3 conditions => 3P3 = 6 permutations
- (1,2,3), (1,3,2), (2,1,3), (2,3,1), (3,1,2), (3,2,1)
- 4 conditions => 4P4 = 24 permutations
- (1,2,3,4), (1,2,4,3), (1,3,2,4), (1,3,4,2), …
•Number of participants must be multiple of number of permutations
Balanced Latin Square
•Latin Square
- Each item occurs once in each row and column
•Balanced Latin Square
- Each item both precedes and follows each other item an equal number of times
