Outdoor Advertising Measurement: An introduction in impression based metrics

Every billboard in America has a unique ID tag identifying the daily popularity of billboards through road counts from various government transportation departments.Daily Effective Counts (DEC’s) help tailor the government measures for advertising models. For instance, road counts count the number of cars travelling in all directions; however,outdoor advertisements only create impressions on those who drive (and the passengers) facing the billboard. Another key component to outdoor reach and frequency calculations is the load factors (or target audience weight), which refine the measurements accuracy by accounting for studied proportions of demographics in a car. Load factors combined with demographic information help identify, on average, the probability specific ages and genders billboards will impress.  Using the DEC, along with target population, we can calculate an impressions estimate of GRP’s, Frequency, and Reach.  Of course, size and the lighting of billboards clearly affect the number of impressions outdoor advertising creates.

Total GRP’s = DEC * Days / (Population/100)

The formula follows the OAAA standard, except altered to reflect total GRP’s instead of only daily GRP’s. Multiplying DEC by Days results in the total number of impressions garnered. By then dividing by the population and 100, we arrive at an estimated percentage of the target population impression.

Frequency = [(Load Factor *Total GRP’s) / 100] + Weight Factor

Load factor is implemented within our reach and frequency calculations to determine the estimated target population tendency of being impressed by outdoor advertising. The additional weight factor is to compensate for the specific type of advertisement (posters = 2, rotaries = 4, permanent bulletins = 6).

Reach = (Load Factor * Total GRP’s)/ Frequency

This raises an interesting question. If reach and frequency equations are so similar, how do we know the calculations are logical? For the sake of simplicity, let’s first exclude the added weight factor in frequency calculations.

This leaves frequency = (Load Factor * GRP’s)/100

reach = (Load Factor * GRP’s)/ frequency.

So, reach = (Load Factor * GRP’s)/ ((Load Factor * GRP’s)/100), incorrectly estimating reach always equaling 100. This concludes that the major difference between frequency and reach estimates is the Weight Factor, suggesting industry methodology believes weight factor distinguishes frequency from reach. However, because reach is calculated using frequency, weight factor does indirectly influence reach.

One of the most notable aspects of outdoor reach and frequency is our analysis of the high frequency and especially high reach measurement possibilities. While frequency is the average times a reached person is impressed by an advertisement, due the nature of modern life, billboards create high frequencies for those who regularly traverse a specific path – emphasizing the importance of location and traffic movements in outdoor placement. High reach numbers occur because of the nature of reach as an impression based measurement. Meaning,  measurements estimate the maximum potential percentage of people seeing the advertisements, and not the percentage of people consciously acknowledging the advertisement (unlike noting scores in publication advertising). Because of the usually long-term contracts for billboard space, it is not unlikely that, once or twice during a year, you find yourself passing a billboard therefore contributing to some of the high reach outdoor media creates. This does not suggest that: a) impressions based measurements are invalid b) billboards are the most effective advertisement medium. We will explore both these points in future posts.

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