What test can I use to find out, if something occurred in a sample by chance?

Question

I have a target audience of people, who ask questions online. My goal is to find out, what types of questions are most frequently asked.

I took a sample of 100 probably random questions and assigned one or more categories to each of them.

Then, I have counted, how often a question of a certain category was asked.

Imagine, question of category A has been asked B times in a sample of 100 questions. How can I find out, whether

1. this type of question is asked often in the total population (i. e. not those 100 random questions, but all questions of my target audience) or
2. the result is a random one (i. e. even though this category occured B times in my sample, in the total population of questions it occurs much less frequent than B percent)

?

What kind of test can I use for that?

Answer 1

Your population is the space of categories, where each question is a sample from the "true" underlying category distribution for your site.

A reasonable first test would be a multinomial test, where the null hypothesis is that the category probabilities are all equal. If it the null isnt rejected, then its plausible that none of the questions are favored.