What purpose do tight music rotations serve?

One of the most common criticisms of commercial radio is it plays "the same few songs all the time" - so why do it?

The logic is simple - the most frequently-played tracks are likely to have proven most popular in that station's music research, and someone is statistically likely to hear one of those tried and tested favourites whenever they tune in.

A common methodology for conducting this research is the auditorium test whereby existing listeners and target listeners are brought together in a room, listen to a load of songs and score each one based on how much they like it.

While likability is the most important data overall, programmers are also interested in familiarity (knowing the song) and burn (sick of hearing the song). These two are particularly relevant to current tracks and determining if a newer song has cut through or been overplayed.

Auditorium testing isn't exactly cheap so doing it more frequently would be costly and if you test too many songs in one session, by keeping people sitting there for too long, productivity sharply decreases thus affecting the accuracy of results towards the end.

However, what you could do is gamble excluding a certain number of huge songs that consistently score well to make way for a few extras - at least for a while.

While technological advancements in recent years make online music testing possible - which some smaller stations have done - this is less reliable as it's conducted unsupervised and unrealistic to think every person who makes a start in their own time will complete the survey and do so correctly.

BBC radio may seem less music-intensive than commercial radio but then you factor out the ad breaks it doesn't have to contend with. This is also the reason BBC stations are better placed to risk playing more songs that maybe aren't as popular or familiar.