The New York Times reports that TV networks have a lot of tricks up their sleeves to manipulate Nielsen ratings:

Labeling a program a special is just one technique. Networks typically “special out” a show when they expect it to fare poorly, against the Super Bowl, for example. Other strategies include front-loading national commercials early in a show and extending the program lengths for hit shows a minute or two into the following hour.

Before getting a bit deeper into this, let's review how the Nielsen ratings work. Nielsen, which is considered the authoritative source for media ratings in the US, estimates that there are about 115.6 million TV viewing households in America. To track viewing habits, they survey two samples. The first is a long-term (12- to 24-month) sample that is paid on a monthly basis according to how many TV's, DVD players, and DVR devices they own (not how much they watch). These households are equipped with a box that sends their viewing to Nielsen every night at midnight. The other sample is group surveyed for a much shorter period of time (7 days, or 8 days if the household owns a DVR) to help Nielsen keep up with trends that may not be present in the larger sample.

Ratings are reported as two numbers: "For example, Nielsen may report a show as receiving a 9.2/15 during its broadcast, meaning that on average 9.2 percent of all television-equipped households were tuned in to that program at any given moment, while 15 percent of households watching TV were tuned into that program during this time slot." (Wikipedia) These ratings can be reported on either a media-market level or for national programs. Whether a network program is considered local or national depends on whether it includes national ads during the scheduled airtime.

So how do networks get tricky within this fairly straightforward system? One way is by labeling a program a special, so that low ratings in a given week (or even hour) don't dampen the average for the year. Another trick is to squeeze all national commercials into the highest-rated portion of a show to boost the rates that you can charge. (This works for local commercials too--typically they are only shown around halftime in the Super Bowl.) Since Nielsen boxes can measure minute-to-minute viewing choices, networks can also get tricky by giving Nielsen a schedule that differs wildly from what you would see in your TV guide: making a program last only 16 minutes, or having it finish a couple of minutes after the hour to pick up new tune-ins from the following program.

The networks all know about these tricks, despite getting frustrated when competitors use them. What is not clear to me is whether the advertisers recognize what is going on and account for it when negotiating for rates. And certainly researchers relying on media data for analysis will want to take a closer look before making conclusive claims. Here is Nielsen's attitude, and one executive's point of view:

A Nielsen executive, who requested anonymity because of confidentiality agreements with clients, said Nielsen did have guidelines for what could be done with shows, but recognized that networks would “format their programs to generate maximum ratings impact — call it gimmicks, or call it spin.”

Unless the gimmick results in something egregiously false, Nielsen does not step in. The worse that might happen would be a sternly worded letter.

“You do everything you can, as long as you can,” said the network program executive. “And then they slap your hand.”

We're in a sweeps period until February 29. Enjoy!