Writing about your N when your N is this and that

Below is a smart way that a study was written up in an article. The article is
by Dawn Poole
A study of beliefs and behaviors regarding digital technology
New Media Society 2007; 9; 771
QUOTE FROM ARTICLE (here's how they talked about the N)

Sample
The survey was administered to Central California students in various courses at junior high (grades 7–8), high school (grades 9–12) and college levels from November 2002 to January 2003. A total of 453 surveys were used in the data analysis. Some of the surveys contained incomplete demographic data or incomplete responses on the Likert scale survey items; therefore, the reported results total less than 453 in several tables.