As the title suggests, there are two main branches of statistics: descriptive statistics and inferential statistics.
Psychologists use descriptive statistics to summarize and describe a group of numbers from a research study. These numbers can be displayed in all sorts of charts and graphs to make information interpretation easier. For example, this chart shows the percentage of students who graduated from a particular university over the course of 10 years:
More in depth, this pie graph shows the race/ethnic demographics of the graduating students:
Although descriptive statistics provide us with ways to present information, it does not offer explanations, and we cannot use it to draw conclusions from the information presented. For example, the first graph tells us the number of students graduating from that particular university increased with the years. But it does not tell us why. We cannot conclude if this increase is due to the hiring of better instructors, an increased number of students attending the university, or implementation of better learning strategies. Likewise, in the pie graph we cannot conclude why more white students graduate from this particular university. Maybe the majority of the graduating students are white because this university is situated in a city where whites are the majority. Whatever the reason, we cannot know. Descriptive statistics does not provide this information.
Inferential statistics go one step further than descriptive statistics. With inferential statistics we can draw conclusions from the data gathered. For example, imagine you are working on a class assignment that requires you to find out what percentage of students in your university are constant procrastinators. It would take you an enormous amount of time and effort to interview every single student in a university of, say, 10 thousand students. So instead, you gather a group of about 100 students (the sample) and get information from them. If 60% of the students within the sample admit they are procrastinators, you can estimate that about 60% of the total college population procrastinate. But of course, not everything is as simple as it seems. Polls and surveys have flaws; these will be discussed in later posts.
- Laerd Statistics
- Statistics for Behavioral and Social Sciences: A Brief Course (college textbook)