Chinese Food

I wanted to compare how the quality of Chinese food varies by neighborhood in New York.  I choose the three neighborhoods I have lived in in NYC as a base.  What I found was that in one out of the three neighborhoods analyzed (10003, 10009, 11205) had one Chinese restaurant and the third has none.  I parsed out a couple other random area codes to see if this was an all around problem and they also had small to no numbers of chinese restaurants.  Looking at the raw data I can see that an ample range of zip codes are reflected but it seems as if the total number is far fewer Chinese restaurants than actually exist.  I wonder if there are many restaurants in NYC that fly under the radar of inspections?  I know Ive seen more than a few with no letter posted on their store window.