Even where diaries are returned, viewing may be poorly recorded for particular demos. The primary example is children. Samples also may be deficient because significant populations are excluded from the sample. Primary examples are students residing in college dormitories and military personnel residing on military bases, neither of which are included in Nielsen samples. In many markets, this excludes large numbers of local television viewers.
Problems also occur when sample households go on vacation.
Nielsen will attempt to make up for the underreporting of minority and younger age group demographics by weighting the diaries they do receive. Consequently, for example, one Hispanic child diary can represent a huge demographic value in the sample. This one diary thus represents a disproportionate value as a result of Nielsen's attempt to correct the undersampling problem. Any mistake, therefore, would be greatly amplified due to weighting. For example, in one instance two children in a sample household were recorded incorrectly as viewing a program of purely adult interest.