Disaggregating data collected for several months and aggregating data collected below the monthly level provides a variety of sources of confusion and error. The person-month structure puts all data at the month level with the appropriate aggregation or disaggregation. The person-month structure is a natural unit because the basic building block of SIPP data is the month. In collecting the data we have chosen to identify all changes except labor force changes as occuring between months. Data on labor foce participation is given at both the weekly and monthly level.
Income is recorded and recoded in monthly amounts.
Data on participation in means-tested transfer programs is recorded on a monthly basis. When analysts look at the SIPP data they see a large array of monthly and non-monthly data. Their problem then is to disaggregate the non-monthly data down to the month. In some cases this has been done for them. Households and families and their characteristics are defined on a monthly basis.