### Ratio

When you use a RATIO statement, the procedure produces statistics requested by the *statistic-keywords* in the PROC SURVEYMEANS statement.

Suppose that you want to calculate the ratio of variable to variable . Let be the value of variable for the th member in cluster in the th stratum.

The ratio of to is

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

where if ,

and if ,

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.

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