 Some programs also go on hiatus so that their television networks can reserve episodes for airing during ratings sweeps, wherein networks compute their television advertising fees based on their programs' ratings during that period.Programs return from a hiatus in time for the sweeps period so as to generate high ratings, and as such usually include special content in programming such as guest stars, controversial and unexpected plots or topics, extended episodes, and finales.Television programs tend to have a hiatus for the late-November, throughout December and early January holidays or the summer if the season does not end before, resuming at some point after, most often mid-January in the case of Christmas and New Year, and September in the case of the summer.