The test procedure for 
count data is sufficiently general
so that it is valid for different assumptions regarding the data. The
one assumption that must remain stringent however is that each
experimental unit be counted only once in the data table.
The following table is a summary of the population proportions where a
single SRS is taken from a single population and each observation is
classified into one cell of an table.
The marginal proportions in this table are the sums of the proportions
in the rows and columns. Here the 
are the row sums and the
are the column sums. The marginal proportions are easily
interpreted as probabilities. Each is the probability that a
randomly selected member of the population falls in the ith row
category. Similarly, each is the probability that a randomly
selected member of the population falls in the jth column category.