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# Counts

 Study on Childhood Weight Statistic Value Count 12 Sum 642 Mean 53.5 Median 45.5 Mode No Mode Min 13 Max 110 Range 97 Standard Deviation 31.0

Let’s use some sample data from a study on childhood weight. Weights from several different children were collected. Here are the different weights in the dataset:

13        36        98        77        42        50
110      22        49        81        26        38

## How Many?

The first descriptive statistic you should know is a count. This is just as simple as it sounds; it is a count of how many items or "observations" you have. If you count how many child weights there are above, you would find that there are 12.

Sometimes in statistics we call this the "n", indicated by a small letter n. So here our n=12.

• Count (n) = 12

## Why do I need to use a count?

Big deal, you’re thinking. Who cares about a count? Well, this number actually gets used a lot in statistics. It is important to know how many observations your dataset contains in order for you to properly evaluate your results.

For instance, if this were a real study being done and you were trying to make a conclusion about childhood weights, would you really trust a study that only had 12 children in it? Obviously, we would need to have more observations to make valid conclusions. But for learning purposes, 12 is a great number to work with.

rev. 29-Aug-2016