Guía para el uso de datos de audiencia Nielsen IBOPE México

For a single minute with a rating of p and given a sample size of n:
Sampling error =
Guía para el uso de datos de audiencia
For a schedule of s spots each with a rating of p (and assuming statistical independence between spots)
then:
Sampling error =
95% Confidence Interval=2 x Sampling Error
Table 11 shows results for schedules of varying compositions but all delivering 200 ratings based upon the
London sample of 459 men.
TABLE 11:
SAMPLING ERRORS FOR SCHEDULES WITH DIFFERENT STRUCTURES
Single Spot TVR Single Spot
% s.e.
20
2.2%
10
3.2%
5
4.7%
1
10.7%
0.5
15.2%
Number
of Spots
10
20
40
200
400
So in theory the total ratings sampling errors are independent of the size of the ratings which make up
the schedule. Certainly the variations in the percentage sampling errors are nothing like the variations in
the single spot percentage sampling errors. In practice the equality of the schedule total ratings sampling
errors will depend upon correlations in viewing between spots.
We can get a feel for whether or not this works in practice by comparing the ITV and Channel 4 components
of each schedule. On average, single ITV ratings are about three times as high as single Channel 4
ratings. In Table 12 the schedule components have been ranked according to total ratings delivered.
Total
TVRS
200
200
200
200
200
Total TVRs
95% c.i.
+ 5.9%
+ 6.3%
+ 6.4%
+ 6.6%
+ 6.6%
33