SIPP is a complex longitudinal survey that is continually addressing sample attrition and nonresponse bias. The 2021 SIPP continued to face data collection complications because of the COVID-19 pandemic and a general lower-than-average unit response rate nationally. 

To monitor and improve data quality during collection, SIPP’s geographic Primary Sampling Unit (PSU) are reviewed to identify areas that have insufficient representation (coverage). Adaptive design case prioritization and active field management are used to achieve both an increase in representativeness and ensure a minimum level of coverage.

Even with these data collection mitigations, the low unit response rate in 2021 SIPP led to item response rates and coverage ratios that do not meet the Census Bureau’s Statistical Quality Standards. The SIPP program creates weights designed to adjust for nonresponse and to control weighted counts to independent population estimates by age, sex, race, and Hispanic origin. However, the magnitude of the increase in (and differential nature of) nonresponse during 2021 data collection likely reduces their efficacy. As a result, data users should use caution when creating estimates using 2021 SIPP data, including the longitudinal 2018 and 2020 Panel subsamples.

Additional information on nonresponse bias for data collected in calendar year 2021 will be available in the upcoming Nonresponse Bias Report for Calendar Year 2021 of the Survey of Income and Program Participation. More details about 2021 SIPP’s unit response rate, sample attrition, and item response rates for SIPP’s key estimates are forthcoming.