
I was recently asked whether I had any data to support the claim that the number of mentions of the LAPD (Los Angeles Police Department) in hip hop lyrics has fallen off in recent years, after peaking in the mid-1990s. The LAPD attracted a lot of angry attention from hip hop artists in the wake of the 1992 LA riots, triggered when four LAPD officers were acquitted of using excessive force in the arrest and beating of Rodney King.
On the face of it, this claim should be easy to check: use a lyrics database to search for hip hop songs mentioning “LAPD”, find when they were released, and look at the trend. In practice, it turns out to be rather more complicated.
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The value of statistical techniques in historical musicology depends on the quality of the available data. The extent and diversity of these sources is considerable, but it is important to remember that they can only ever illuminate a small proportion of the musical world.
Triangulation is a research technique that involves looking at the same thing from two different perspectives. In surveying, it enables positions and distances to be calculated by measuring angles from two locations. In the social sciences, it can increase the reliability of conclusions if they are found by two (or more) different methods. And in statistical historical musicology, looking for the same works or composers in two or more datasets can tell us a lot about the characteristics of the datasets, and about the works’ patterns of survival or dissemination. 
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