Introduction to statistics

PRESENTATION

Pie Chart

Pie Chart: a special chart that uses "pie slices" to show relative sizes of data.

Imagine you survey your friends to find the kind of movie they like best:

Table: Favorite Type of Movie
Comedy	Action	Romance	Drama	SciFi
4	5	6	1	4

You can show the data by this Pie Chart:

It is a really good way to show relative sizes: it is easy to see which movie types are most liked, and which are least liked, at a glance.

How to Make Them Yourself

First, put your data into a table (like above), then add up all the values to get a total:

Table: Favorite Type of Movie
Comedy	Action	Romance	Drama	SciFi	TOTAL
4	5	6	1	4	20

Next, divide each value by the total and multiply by 100 to get a percent:

Comedy	Action	Romance	Drama	SciFi	TOTAL
4	5	6	1	4	20
4/20 = 20%	5/20 = 25%	6/20 = 30%	1/20 = 5%	4/20 = 20%	100%

Now to figure out how many degrees for each "pie slice" (correctly called a sector).
A Full Circle has 360 degrees, so we do this calculation:

Comedy	Action	Romance	Drama	SciFi	TOTAL
4	5	6	1	4	20
20%	25%	30%	5%	20%	100%
4/20 × 360° = 72°	5/20 × 360° = 90°	6/20 × 360° = 108°	1/20 × 360° = 18°	4/20 × 360° = 72°	360°

Now you are ready to start drawing!
Draw a circle.
Then use your protractor to measure the degrees of each sector.

Here I show the first sector ...

Finish up by coloring each sector and giving it a label like "Comedy: 4 (20%)", etc.

(And don't forget a title!)

You can use pie charts to show the relative sizes of many things, such as:

• what type of car people have,
• how many customers a shop has on different days and so on.
• how popular are different breeds of dogs

Your turn: Student Grades

Here is how many students got each grade in the recent test:

A	B	C	D
4	12	10	2