"The unit of analysis in this study is the media market or designated market area (DMA) as defined by Nielsen Media Research. There are a total of 210 DMAs in the US, which are geographic areas receiving common television broadcasts or radio programming; they may also receive other similar media content, such as newspapers or Internet advertising. Hence, although there is heterogeneity within DMAs, they represent a coherent unit of analysis because residents may be exposed to similar social messages influencing racial attitudes."