Describe FAQ/combinatorics/inst2rep1 here.

= Derivation of 1 instance of 2 replicates of one of 92 stimuli in a sequence of length 6 =

An example of 1 instance of 2 replicates is AAABCD ie three repetitions of the same stimulus in the sequence of length 6. There are (6 choose 3) = 20 ways of ordering the repeated stimulus. These are

{{{
123
124
125
126
134
135
136
145
146
156
234
235
236
245
246
256
345
346
356
456
}}}

There are 92 stimuli that can be repeated and there would be three distinct simuli not equal to the repeated stimulus in the remaining three positions giving 92 x 20 x 91 x 90 x 89 possible combinations of a single incidence of 2 repeats of a stimulus giving a probability when divided by 92^6 of 0.002.