Writers of long, complex sentences often lose track of the subject, which can result in a mismatched verb. Sometimes
it happens because the two or more items that make up the subject seem to function as one unit, and thus the writer
thinks it's a singular subject. Sometimes it happens because the subject seems to be some other word in the sentence.
Consider the following, which are all incorrect (my explanation in bold follows most sentences):
The history of the National Intramural Recreation Association and its importance to the development of professionals and programming is discussed. (Two things, history and importance, are discussed. It needs a plural verb.)
The length, frequency, and duration of the activity refers to the length of time of an individual class meeting, the number of times per week the class meets, the number of weeks the class meets, and how often the class is held per semester or quarter. (The subject is length, frequency, and duration. The verb should be refer.)
The availability of playing space and equipment are major factors that determine when and whether an extramural event will occur. (Here the subject is availability, not playing space and equipment. Therefore, it needs a singular verb, is, and a revision to the object: the major factor that determines.)
Dividing wet areas (showers, steam rooms), toilet areas, and dry areas (dressing, locker storage) make facilities comfortable for users and easy to maintain. (Here the subject is the gerund dividing, which is singular. The subject is not wet areas, toilet areas, dry areas.)
Target audience data is important to the sponsor. (The word data is always plural. The singular form of the word is datum.)
The media are biased. (See Bill Walsh's article "Call me a heretic, but 'media' isn't always plural" at www.theslot.com/media.html.) Here's an excerpt of Walsh's argument, which I agree with:
"Media" as a plural means "more than one medium." Fine. If you're using the word as a plural, make it plural. But that's not usually the way it's used nowadays. It's used as a synonym for "press," as a collective noun meaning "the representatives of each medium."
Commitments should be solicited while excitement and enthusiasm is still fresh in the sponsor's mind. (One could argue that excitement and enthusiasm count as one unit, but they don't. The subject is plural. It needs a plural verb.)
Analysis leads to planning, execution, and control, which ultimately leads to further analysis. (Analysis does not lead to analysis; planning, execution, and control lead to further analysis.)