This material is from section 1.1.

Statistics can be though thought of as being made up of two branches. Combined, these fill in the definition you read in the intro.

Hint: if you prefer to review a video, scroll down!

Descriptive statistics

This is exactly how it sounds. Descriptive statistics is all about describing the patterns present in a data set. This could be through the use of tables or graphs, or this could be numerical like calculating a mean.

Why is this useful?

Imagine you were given a list of 1000 numbers representing the GPA of a group of students. If you really wanted to understand this list, this wouldn't be very useful at all! Instead, maybe you would calculate an average, or, maybe you could break the data up into groups and plot how many people have a GPA above 3.0, etc. Only then could you really see a pattern.

Note: you can apply descriptive statistics to data from a population (large group of interest) or to a sample (small group selected from the large group of interest).

Inferential Statistics

Most of statistics is concerned with using a sample to better understand a population. This may be in order to estimate some unknown value from the population, such as "What percentage of people support this candidate for office?" or to determine whether a hypothesis like "This medication lowers blood pressure by more than 1%" is likely to be true.

So, again, what sets this apart is that you are using sample data to understand a population. The sample may be the group on the blood pressure medication or the group that were surveyed about their political views.

Why is this useful?

As we will review later, it is often impossible to look at an entire population. Therefore, inferential statistics allows us to make conclusions using a much smaller group! One tool of inferential statistics, hypothesis testing, is used in medicine to determine whether a medication is actually helpful or not. In other fields, hypothesis testing is used to answer questions such as whether a website design change would likely result in increased sales.

Video

The following video does a great job at explaining the difference between these two branches of statistics.

Click NEXT (bottom right) to continue to section 1.2.