For most purchases of a tangible product, a buyer is able to examine the product before accepting it. They can punch it, toss it, try to break it, look at it from different angles and be sure it is free of defects.

For services and other intangibles it’s not so easy to be a responsible purchasing agent. When making a commitment to buy a service to be performed in the future, it’s important to have a clearly stated statement of expectations, guarantees for delivery of expected value and terms of compensation in the event the desired value is not received. It also requires a good deal of trust that the value to be received when the service is complete will in fact prove to be a good deal.

Advertising time and space is a particularly tricky thing to buy, in many regards not unlike picking stocks. You’re buying advertising time or space based on an expectation of what it will be worth in the future, projected from a track history of what it was worth in the past. 

To determine the value of media time on a TV program or radio station, media buyers look at audience ratings. These are measurements of the size and demographics of their audiences taken months earlier, to project what audiences these stations and programs will receive in the future. 

With TV and radio stations and networks constantly battling to steal audience from each other, the actual audience reached by the station at the moment your commercial runs could be very different – higher or lower – than what you expected. After the buy has run, it’s essential to see what audience levels you actually reached in relation to what you paid.  This is called a post-buy analysis.

Definition – Post-buy Analysis

A comparison of the actual advertising schedule run to the original expectations of the schedule as purchased, considering adherence to buy specifications, actual audience achieved as measured by audience ratings services when available, and conformity to standard industry practices.

The term post-buy analysis is used primarily in relation to broadcast media (and more frequently performed for TV schedules than for radio), but a similar type of stewardship should be performed for purchases of print and outdoor media as well. 

This article will not explore post-buy analysis of online media.

Those readers less familliar with media terminology and measurments may find it helpful to review the following Best Practice papers:

• Principles of Media Planning  
  by: Barbara Langbecker and Enza V. Chiodi
  This tutorial covers the basics of formulating a campaign from setting targets to selecting the media mix and frequency.
   
• Understanding Media Math 
  by: Enza V. Chiodi and Jill Newman
  This tutorial defines the terms and demonstrates the use of various media measures for both broadcast and print campaigns.