BARB stands for the Broadcasters' Audience Research Board which measures television viewership across different channels in the UK. It provides data to broadcasters on how many people watched various programs so they can determine what shows to air on which channels and at what times to maximize viewers. The data shows that period crime dramas like Death Comes to Pemberley tend to attract older audiences, Agatha Christie's Marple appeals more to middle-aged and elderly viewers, and Midsomer Murders has a female and more upmarket audience with fewer children watching.