When you use a RATIO statement, the procedure produces statistics requested by the statistickeywords in the PROC SURVEYMEANS statement.
Suppose that you want to calculate the ratio of variable Y to variable X. Let be the value of variable X for the jth member in cluster i in the hth stratum.
The ratio of Y to X is

PROC SURVEYMEANS uses the Taylor series method to estimate the variance of the ratio as

where, if , then









and if , then

The standard error of the ratio is the square root of the estimated variance:

When the denominator for a ratio is zero, then the value of the ratio is displayed as '–Infty', 'Infty', or a missing value, depending on whether the numerator is negative, positive, or zero, respectively; and the corresponding internal value is the special missing value '.M', the special missing value '.I', or the usual missing value, respectively.