Find the mean value of the following expressions:

∑

i Y

r i Y s

i Y t

i

, ∑

i≠j Y

r i Y s

j Y t

j

, and ∑

i≠j≠k Y

r i Y s

j Y t

k

.

Hence find the symmetric functions that are unbiased estimates of κ

rst κ

rκ

st and κ

rκ

sκ

t

. By combining these estimates in the appropriate way, find the symmetric functions that are unbiased estimates of κ

r,s,t

, κ

r,st and κ

rκ

s,t

.