# Learn By Doing – Periodontal Status and Gender

Here again is the table regarding the periodontal status of individuals and their gender. Periodontal status refers to gum disease where individuals are classified as either healthy, have gingivitis, or have periodontal disease.

We will now use this data as our “population” and consider randomly selecting one person.

Now let’s look at something new!

Suppose we select one person at random, what is the probability that the person is male and has a healthy periodontal status?

When looking at the table, we need to determine how many individuals are both male and have a healthy periodontal status. See if you can determine the correct probability for this question. The table is copied below for easy reference.

In all of the questions above, the probability can be easily calculated by simply counting how many individuals satisfy the event or combination of events. This brings us back to our earlier principle:

**PRINCIPLE: If you can calculate a probability using logic and counting you do not NEED a probability rule (although the correct rule can always be used)**

Now let’s go one step further and see if you can use logic to answer a slightly more difficult question.

We will return to the previous question when we introduce the probability rule which applies.

**Comment:**

- Note that if this data is indeed representative of our true population of interest, then in this example, we would be estimating the probabilities of interest in the population using the information contained in our sample. Remember this is one of our eventual goals in this course!

This document is linked from Basic Probability Rules.