SIPP includes person weights that estimate the number of people in the target population that each person represents. In general, since population units may be sampled with different selection probabilities and since response rates and coverage rates may vary across subpopulations, different responding units represent different numbers of units in the population. The use of weights in survey analysis compensates for this differential representation, thus producing estimates that relate to the target population.

SIPP weights vary due to differential sampling rates because of oversampling and because response and coverage rates vary across subpopulations. For example, in the 2021 SIPP, the final person lower quartile weight is 3,600 and the upper quartile weight is 7,200 (the maximum weight is 56,000). A respondent with a final person weight of 3,600 represents 3,600 people in the U.S. population for the reference month, whereas a respondent with a weight of 7,200 represents 7,200 people.

The decision of which weight to use for a given analysis depends on 1) the population the results are intended to apply to, and 2) the duration of interest for that analysis. The weights in the SIPP files are constructed for sample cohorts grouped by:

• Month (e.g., the reference month weights)
• Year (e.g., the calendar year weights), and
• Multi-Year periods (e.g., longitudinal weights that cover consecutive two-, three-, or four-year periods).

Using these weights, data users can choose to base their analyses on:

• A cross-sectional sample at a given month,
• A sample that provides continuous monthly data over a year, or
• A longitudinal sample that provides monthly data over more than one consecutive year.

Using longitudinal samples, data users can study issues such as the dynamics of program participation, lengths of poverty spells, and changes in other circumstances (e.g., household composition). The multi-year longitudinal weights include weights for the cohort of respondent who have positive calendar year weights for every year of the longitudinal period, regardless of panel.

How Weights Are Constructed

The basic components for all the different sets of weights are the same, namely:

• A base weight that reflects the probability of selection for a sample unit;
• An adjustment for subsampling within clusters;
• An adjustment for movers (in Waves 2 and beyond);
• A nonresponse adjustment to compensate for sample nonresponse;
• An adjustment for combining sample cases from multiple panels (if overlapping panels cover the reference period); and
• A post-stratification (second-stage calibration) adjustment to correct for departures from known population totals.

Please see the SIPP Users’ Guide specific to your year or panel of analysis for more guidance on using weights.