While some stations play all kinds of electronic dance music, others (mainly pirate radio stations) focus on particular genres. This format is popular in England, Germany, Netherlands and some other countries, but less so in the United States (where dance is a niche format often exclusive to internet radio stations). However, the number of U.S. stations airing such content has grown; five terrestrial radio stations in the U.S. with a purely dance-oriented format (one of which airing it part-time during the night and early-morning hours) report their airplay to the Billboard Dance/Mix Show Airplay chart, while top 40 and rhythmic stations may also air EDM songs that have crossed over onto pop-oriented charts due to the recent growth in mainstream popularity of dance music. Christian and gospel radio stations usually plays the popular Contemporary Christian music, others playing Gospel music and/or Praise and worship. K-Love and Air1 are among the most popular Christian radio stations. In the United States, Christian music stations (especially ostensibly noncommercial ones) often rely heavily on brokered programming: a Christian music station typically only carries music for part of the day, with the rest of the day filled by evangelists who pay to place recordings of their sermons on the station. Some music radio is broadcast by public service organizations, such as National Public Radio or the BBC. In the United States, public radio is typically confined to three formats: news/talk, classical music, or jazz, the last of which is declining rapidly as of the late 2000s. In other countries, where national broadcasters hold significantly more clout, formats can vary more widely. Community radio often relies heavily on the music format because it is relatively cheap and generally makes for easy listening. Commercial stations charge advertisers for the estimated number of listeners. The larger the audience, the higher the stations' rate card can be for commercial advertising. Commercial stations program the format of the station to gain as large a slice of the demographic audience as possible. A station's value is usually measured as a percentage of market share in a market of a certain size. The measurement in U.S. markets has historically been by Arbitron, a commercial statistical service that uses listener diaries. Arbitron diaries were historically collected on Thursdays, and for this reason, most radio stations have run special promotions on Thursdays, hoping to persuade last-minute Arbitron diarists to give them a larger market-share. Stations are contractually prohibited from mentioning Arbitron on the air.