Reliability of Estimations, 1996

Because the statistics presented in the 1996 National Home and Hospice Care Survey are based on a sample, they will differ somewhat from figures that would have been obtained if a complete census had been taken using the same schedules, instructions, and procedures.  The standard error (SE) is primarily a measure of the variability that occurs by chance because a sample, rather than the entire universe, is surveyed. The SE also reflects part of the measurement error, but it does not measure any systematic biases in the data. The chances are about 95 in 100 that an estimate from the sample differs from the value that would be obtained from a complete census by less than twice the SE.  However, SE's typically underestimate the true errors of the statistics because they reflect only errors due to sampling.

The SE's used in this report were approximated using SUDAAN software. SUDAAN computes SE's by using a first-order Taylor approximation of the deviation of estimates from their expected values. A description of the software and the approach it uses has been published. Although exact SE estimates were used in tests of significance in this report, SE's for aggregate estimates presented may be estimated using the general formula:

where X is the estimate and RSE(X) is the relative standard error of the estimate. The relative standard error (RSE(X)) may be estimated using the following general formula:

where X is the estimate and A and B are the appropriate coefficients from table I.

To approximate the relative standard error (RSE(p)) and the standard error (SE(p)) of a percent p, the appropriate value of parameter B from table I is used in the following equation:

where p = 100 · X/Y, X = the numerator of the estimated percent, and Y = the denominator of the estimated percent and

The standard error of a percent is valid only when one of the following conditions is satisfied: the relative standard error of the denominator is 5 percent or less or the relative standard errors of the numerator and the denominator are both 10 percent or less.