3.1 TWO-VARIABLE DATA SETS Consider the variables family income

and family expenditure. Increase & decrease togetherChange in one variable is accompanied by

change in the other variable Price and demand of a commodity are

related variablesWhen Price increases, demand decreases

and vice versa

2-VARIABLE DATA SETS If the change in one variable is

accompanied by a change in the other, then the variables are said to be correlated.Family Income & Family Expenditure are

correlatedPrice and Demand are correlated

RELATIONSHIP BETWEEN VARIABLES Correlation can tell you about the

relationship between variables. It is used to understand: Whether the relationship is positive or negative The strength of the relationship

In the case of family income & expenditure, they both increase and decrease together, so this is a positive correlation

In the case of price and demand, if one increases, the other decreases, so this is a negative correlation

ONE VARIABLE DATA

A “variable” is an attribute that can be measured

One-variable data has measures for one attribute

Recognize them when you see:Bar GraphsCircle GraphsTally Charts

One-variable data can be measured using:Mean, Median, Mode

These are “Measures of Central Tendency”

TWO-VARIABLE DATA Measures for 2 attributes Recognize them when you see

Table of ValuesOrdered PairsScatter Plots

Two-variable data can be analyzed by looking for a trend or pattern in the relationship.

This trend may be:LinearQuadraticExponential

1 OR 2 VARIABLE DATA?

Blood Types Percent of People

A 43%

B 8%

AB 3%

O 46%

Choose a type of graph to represent the data. Describe as one-variable or two-

variable data.

One Variable Data on a Pie Chart

Blood Types

A B AB O

1 OR 2 VARIABLE DATA?

Choose a type of graph to represent the data. Describe as one-variable or two-

variable data.Instructiona

l HoursDriving Test

Score

10 78%

15 85%

21 96%

6 75%

18 84%

20 45%

12 82%

4 6 8 10 12 14 16 18 20 220%

20%

40%

60%

80%

100%

120%

Driving Test Scores

Instructional Hours

Dri

vin

g T

est

Sco

res

Two-Variable Data on a Scatter Plot

3.1 HOMEWORK p. 147 #2, 4, 6, 9