Technical Properties of the Arbitron PPM System

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Arbitron's Portable People Meter (PPM) system is currently replacing its old paper diary system. There are a number of radio veterans questioning PPM's accuracy because listenership reports have frequently been quite different from those of the diary system.

After analyzing public information, I conclude that this system appears to be technically sophisticated and well conceived; it can be expected to be extremely reliable when tested under "typical" conditions. However, a more careful analysis suggests that there may be real-world scenarios that dramatically degrade PPM performance. Regardless of how much testing Arbitron performed before releasing the PPM system, the real world of thousands of radio stations exposes the system to an almost infinite variety of idiosyncratic properties of particular programs, speaking styles of announcers, and listening environments.

Radio stations that believe their listenership has been inaccurately reported by the PPM system may wish to determine if their context deviates from the assumptions upon which the PPM system is designed. Though I conducted a comprehensive search of the publicly available literature, I found no discussion of these assumptions, much less information on how to compensate for them.

We respect that, for legal and/or economic reasons, Arbitron may not be willing or able to share all the technical details of its PPM system with our industry. Our industry, therefore, needs to do its homework.

This article explores the technical design of the PPM system in relatively non-technical language so that station managers, programmers, and engineers can understand the possible implications of these "hidden" assumptions. Further, it frames the relevant questions that we should be addressing and provides suggestions for experiments to evaluate the PPM system in each station's context.

Background and Overview

I've been asked by several of my radio engineering colleagues to comment on the technical properties of the PPM audience measuring system. Inquirers were particularly interested in possible technical explanations of why some program formats on some stations have received dramatically lower audience ratings compared to that of the old diary system.

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