Are there any related observations that are not included in the database?
In Verviers, where we have taken a letter sample, we include all persons in the household of a person in the sample. Other samples are complete within geographic areas. Some samples include vital registers (marriages, deaths) with information on parents, who may have been deceased at the time the information was recorded.
How do the units of observation enter observation?
Observation begins in three ways:
1. a record in a nominative list, usually derived from a census.
3. migration into the commune
How do the units of observation leave observation?
3. Censored by the end of the last population register in a series.
When an exit date is not available, we can identify the interval in which the exit occurred, because of regular censuses.
Are some entry or exit dates unknown?
About 10 to 30 percent of life histories end without an explicit date of exit. We can usually verify that out-migration occurred by checking the next population register.