Gross rating points (GRPs), a concept we introduced to public TV several years ago, deliver more useful station data than, "My station got a four rating, five share." And GRPs are easy to measure; just add the ratings for the program or daypart in question. GRPs permit comparison of series, dayparts, specials, or programs in a sweep or over many seasons.

Here we compare the DMA average weekly ratings for NOVA for two years:

Table 3 NOVA
Week 1 2 3 4
1992 6 1 4


1993 6 2 6 1

Both years there were 15 GRPs for NOVA (an average 3.75 rating for each sweep). But GRPs tell us more: note that titles varied in appeal in the market. The programs in weeks 2 and 4 in 1993 may not be very desirable to a programmer looking for a strong repeat.

GRPs measure viewing tonnage, whereas the cume is more like the oil dipstick in a car. As in cume measurement, GRPs can be assessed for specific dayparts or for the whole week. Let's consider November prime time GRPs for three stations by day of the week.

These numbers represent the 28 days of prime time. The Station X numbers show that UHF stations still pay for signal shortcomings. It is rare that a UHF station exceeds 400 GRPs in a prime time. Naturally, the metered markets have an advantage in GRP measurement. In November, metered stations had the largest prime time GRP totals, with some exception.

Table 4 Station W

Station X

Station Z
Monday 76 39 55
Tuesday 99 39 76
Wednesday 127 70 93
Thursday 110 52 72
Friday 116 54 76
Saturday 77 34 86
Sunday 64 42 67
Total 669 330 525

The hour also has a great impact on GRPs. In general, the first hour of prime time (8 p.m. East/West Coast; 7 p.m. Central/Mountain time zones) delivers around 40 percent of a station's total prime-time audience, the last hour less than 30 percent. Any program placed in the first hour has an advantage. Many public TV stations use the last hour for limited-appeal programs, so HUTs and programming interact to produce lower ratings.

GRPs may be used to compare stations and dayparts, and to demonstrate station and system trends. A station's GRPs, in relation to its cume, can measure viewer frequency and turnover, concepts that we will explore later. Too few GRPs show a station isn't efficiently attracting and maintaining an audience. We have not yet dealt with who is attracted to what kind of product in a typical public TV schedule -- demographics and program-type appeal.

This chapter was previously published in Current on 2/17/88.

copyright 1998 Trac Media Services, Inc.