Professor perlman was interested in comparing two textbooks to determine whether one used more sexist language than the other. perlman counted the number of times a gender reference appeared in each book. perlman was doing

Manifest content coding.

Explanation:

 Manifesting the content coding is the process in which we analysis the content of the data by proper interpreting the various types of given data sources.

The manifest coding is the one of the type of technique in which the tangible surface of the content are basically distinguished from the latent content.

By using the manifest content coding technique, we comparing the various types of words and phrases.

Therefore, Perlman using the manifest content coding for comparing different types of textbooks for determine the sexist language used in the content.