What are Sweeps
Nielsen collects television viewing habits of audiences and in 1954 they introduced a four week measurement over four months (February, May, July, and November) to better record these habits – now known as Sweeps.
These handwritten seven-day diaries were collected in the Northeast and then Nielsen “swept” across the country to collect the logs until it reached the West Coast viewers.
Sweeps are now used to impact advertising rates. In a network’s advertising plan a half-hour primetime show will normally run six minutes of national ads and two minutes of local advertising. Local advertisers base their advertising rate on ratings collected during Sweeps.
Nielsen measures 210 markets (DMA or designated market area) where 56 are metered markets (estimated automatically instead of journaled).