Central Tendency and Variability
Why is this Important?
If you are going to understand a situation, you will need to able to summarize it. You will need to present the key elements of a data set to someone in a manner that makes the point. You will need to present the data set in a way that facilitates decision-making. You may be asked.
Data Types
Psychologists collect various kinds of data. The data could be numerical scores, people’s ranking of some item, or things like gender or race. Each type of data goes by a different name.
| Numerical scores are called: | measurement data. |
| Rankings are called: | ordinal data |
| Things like gender are called: | categorical or nominal data. |
You want to summarize each. How to do it? You will learn that summarize data, you will need to determine:
| Measures of central tendency: | They tell you about the most typical scores |
| Measures of variability | They tell you about how the scores are spread out |
Why is knowing this important?
Let me tell you why you want to know this kind of information. Let’s say that when you graduate, you can’t find a job. So you decide to open a small business – it will be a running and outdoor shoe store for men. You like the outdoors and exercise- so this will be neat.
You find a location. However, you need stock. You borrow from you Dad enough money to buy 1000 pairs of shoes. To make life easy for this example, let’s say we forget about different styles, different widths and half sizes.
What should we buy? What should we stock?
Well, I’m a size 12. So I go buy a 1000 size twelves? Most you will understand that is a bad idea. Not that many guys are size 12.
Someone tells us that the average male shoe size is 9.
We go buy 1000 size 9 pairs of shoes
What happens to our store and us?
We go broke!
Let’s look at our OUT of BUSINESS sale table! What do you see!
Maybe the average shoe size is Size 9 but is everybody size 9? NO! We sell two hundred size 9s but we are have no shoes for the little feet or big feet guys.
Gosh Darn! (You would probably say something else and your father certainly will).
So we ask Dad and Mom for more money to try again. To avoid this error, we buy 1100 shoes and spread them out.
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We buy: 1000 size 5 pairs 1000 size 6 pairs 1000 size 7 pairs 1000 size 8 pairs 1000 size 9 pairs 1000 size 10 pairs 1000 size 11 pairs 1000 size 12 pairs 1000 size 13 pairs 1000 size 14 pairs |
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To the right you see our display. We open the store again and WE STILL GO BELLY UP!
Why?
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