1. Population and Demographic Data
Types of Errors
Homework: 
Today’s Topics:
Types of error
Errors in the reporting of age data
Lecture no. -19

2. TYPES OF ERROR in demographic data

3. Two principal types of error influence the accuracy of census coverage: omissions and counting errors (Ericksen and DeFonso, 1993).
Omissions include all of the people who were not counted but should have been counted.
Counting errors include erroneous enumerations, such as a person being counted twice, counted in the wrong geographic location, or counted when he or she is not eligible to be included (i.e., “out-of-scope”). Counting errors also include fabricated cases and those that have insufficient information.

4. The sum of omissions and counting errors is designated gross coverage error.
Typically, a census will contain more omissions than counting errors, with the result that there is a net under enumeration (i.e., net undercount).
Most users of census data are more concerned with the net undercount.
As a result, a variety of methods have been developed over the past 50 years to assess the degree to which a census underestimates the true population size.

5. Errors in the reporting of age data

6. The errors in the reporting of age have probably been examined more intensively than the reporting errors for any other question in the census.
Three factors may account for this intensive study:
many of these errors are readily apparent,
measurement techniques can be more easily developed for age data, and
actuaries have had a special practical need to identify errors and to refine the reported data for use in the construction of life tables.

7. Errors in the tabulated data on age may arise from the following types of errors of enumeration:
coverage errors,
failure to record age, and
misreporting of age.

8. For example, the group of persons reporting age 42 in the census consists of (1) persons whose correct age is 42 and (2) those whose correct age is over or under 42 but who erroneously report age 42. The latter group is offset partly or wholly by (3) the number erroneously reporting “out of” age 42 into older or younger ages. The difference between groups 2 and 3 represents the net misreporting error for age 42. In addition, the census count at age 42 is affected by net under enumeration at this age (i.e., by the balance of the number of persons aged 42 omitted from the census and the number of persons aged 42 who are erroneously included in the census).

9. Question???