National EMSC Data Analysis Resource Center
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
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.
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.