Over time, the Nielsen system of determining who's watching what on TV has become one of the most important aspects of the television business. Nielsens play a part in determining what companies advertise on certain shows, what shows should air in each timeslot, what shows are going to be kept on the air for a long time, and what shows are about to die.

It was Star Trek's low Nielsen ratings that led NBC to nearly cancel the series after one season and eventually cut the show's run at three years. By the same token, it was TNG's outstanding Nielsens that persuaded Paramount to give DS9 and Voyager the green light.

Despite Nielsen's influence in Hollywood, it definitely isn't a system that is easy to understand. Hopefully, this can serve as a little help in understanding the complex system.

This article will cover the most commonly seen ratings in the press and on the Internet: Homes, demographics, the share for each, and the overnights, which include homes and demographics, but with a smaller sample.

In the most broad of terms, the Nielsen ratings are percentages without a "%" sign. A 13.3 homes rating means that 13.3% of the homes in America watched that show. A 3.4 men 25-34 rating means that 3.4% of the men aged 25-34 were tuned in. Remember that and this article itself may become less confusing.

The United States has roughly 99.4 million homes with televisions in them and about 230 million people living in those homes. The most common measurement that you'll see in the press and on the Internet uses homes rather than people. Each ratings point represents 1% of the television homes in America or 994,000 people.

Say, for instance, an episode of Voyager gets a 4.0 rating; that means 3,976,000 homes were tuned into that show. It also means that 4.0% of the homes in America with televisions were watching Voyager that week. If Voyager had a very good week and earned a 4.5, that would mean 4,473,000 homes or 4.5% of American homes were watching that particular episode.

If you hear "The Super Bowl earned a 65.5 rating," you can assume that the speaker is referring to the homes rating. Homes is essentially the default type of rating used by the press and Internet sites.

While homes deals with the 99.4 million TV homes in America, demographic ratings deal with the 230 million people in America. The entire population is broken into groups (usually by age and sex in reference to the Nielsens) and then referred to in a way similar to the way homes are. A 4.5 men 25-34 rating means that 4.5% of the nation's population of men aged 25-34 was tuned in.

Slightly more complicated is the calculation of the share. A television show's share is the percentage of televisions *on* that were tuned into a particular show. For instance, there are 99.4 million homes, but maybe only 60 million have their TVs turned on at 9pm on Wednesday when Voyager airs. That means that while the show's rating could be a 4.0, its share would be 7. Although only 4.0% of the total television homes in America (3,976,000 homes) were watching Voyager, that represented 7% (6.6% to be exact) of the television homes that had their TVs turned on.

Share is calculated in the same way for demographic numbers -- if 5 million women 18-49 watched a show, the standard rating would be a percentage of *all* the women aged 18-49 that 5 million women represent. The share, on the other hand, would be the percentage 5 million women represent out of all women 18-49 who were watching TV at the time.

Share is only calculated for network shows that air nearly simultaneously across the nation. It's not calculated for syndicated shows. Syndicated shows don't air on a network like UPN, the WB, Fox, NBC, CBS, and ABC, they're sold directly to individual stations and air at different times across the nation. TNG and DS9 were syndicated shows, Voyager is a network show.

So how is this important for Star Trek?

All of the ratings discussed so far have been from the complete tally of Nielsen's entire sample nationwide (everyone in the country that has a Nielsen meter). Another kind of rating, and the final kind that you'll see commonly discussed about Voyager on the Internet is the overnight rating. The overnights are very similar to the kinds of ratings discussed earlier, but are taken from a much smaller sample than the usual national ratings. Overnight ratings are determined from 46 of the largest television markets in America (a market being a city and the surrounding areas) as opposed to the entire nation. Overnights are released faster (now about 14 hours after an episode airs in the case of Voyager) and are typically higher than the national rating, the rating that includes the entire nation. Overnights, in the end, aren't as significant as the national ratings, but serve as an early indicator of how a show will perform in the end and show how an episode performed in just the larger cities (a significant measure for UPN and Voyager because UPN is shown in most large cities, but not in some of the less populated areas). Share, the demographic numbers, and homes are all calculated in the overnights.

A question that many have asked is "How does Nielsen calculate all of this stuff?" The answer certainly doesn't inspire too much confidence in the ratings themselves. Of the 99.4 million homes in the US, 5,000 are monitored by Nielsen every week of the month. These are all monitored with a small box on the television that automatically tells Nielsen who is watching the TV and what show they're watching. During four months of the year, November, February, May, and July, over 100,000 diaries are also sent out to people to fill out with their viewing habits for a week. That amounts to less than .1% of the population, even during the four sweeps months. And yes, Nielsen has come under fire by consumer groups and the networks themselves, but it still remains extremely influential despite its shortcomings in the sample size and calculation. Because there's typically more data for November, February, May, and July (the sweeps months), they have come to be far more important to advertisers (and therefore the networks as well). You'll see more high-powered specials and episodes during the four sweeps months than you will at any other time.

Bare in mind, the information above only scratches the surface of the Nielsen system. They compute over 4,000 gigabytes of data every day for studios and networks, it's certainly not something that can easily be broken into one short article. As a general rule, however, the homes percentage will be the most important to you, with share and the demographic percentages just down on the list.

Nielsen itself doesn't cancel shows, nor does it have any direct say over what happens in Hollywood. Nielsen essentially functions as a gauge of how popular any given show is -- a gauge that networks and studios pay very close attention to. Some have asked "Why does it matter if Voyager gets low ratings?" It matters because if Nielsen, even with its flaws, says people aren't watching, the show runs the risk of getting canceled. What's worse, if Trek's ratings as a whole stay too low too long, the franchise could be forced into a television hiatus. In the coming weeks, I'll follow this up with an analysis of Trek's ratings successes and failures over the last 12 years since TNG debuted in 1987 -- that article will include Trek-specific applications of the ratings tools in this article.