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
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PROC SURVEYMEANS uses the Taylor series method to estimate the variance of the ratio as
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where if ,
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and if ,
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The standard error of the ratio is the square root of the estimated variance:
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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.