Deriving State-Level Estimates from Three National Surveys: A Statistical Assessment and State Tabulations. A. The Proportion Nationally with the Characteristic


As mentioned in Section II, the accuracy of state-level estimates of proportions is a function of the proportion of the population with the characteristic and the effective sample size. Table 1 shows the proportion of the population in each state estimated by the March 1996 CPS to live below poverty, and the actual sample sizes from which the proportions are estimated. In general, approximately 15 percent of the population are estimated to live in poverty, with approximately double that rate for minorities. The overall rates vary across states, from six percent in New Hampshire to 27 percent in New Mexico. However, many of the state estimates for minorities that differ greatly from the national numbers may be a result of extremely small sample sizes. For example, all state estimates with less than 10 percent or 50 percent or more of their black or Hispanic populations living below the poverty line are based on samples of fewer than 50 minority respondents. The estimate of zero percent of blacks in North Dakota is based on a sample of only two blacks. This demonstrates why great caution is needed before using any state-level estimates. For purposes of this assessment we will use the national proportions, rather than the very unstable state estimates, when calculating precision for each state. For example, rather than using state-specific poverty rates to determine the minimum cell counts for each subpopulation for each state, we use the national poverty rate to determine the threshold applied to each subpopulation across all states. Detailed tables for each of the states are provided in the appendices.

Table 2 provides the national estimates of the proportions with each characteristic based on the CPS and the SIPP. It is important to remember that the estimates reflected in this table do not cover the same time period. These are the values used in the assessment of the surveys' ability to produce accurate state-level estimates.

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