1. Graphs, Good and Bad

2. Two types of variables
Categorical variables- places individuals into one of categories or groups
Examples: gender, ethnic groups, model of car, etc
Quantitative Variables – take numerical values for which arithmetic operations such as adding and averaging make sense.
Examples: Age, weight, income etc.

3. Starting with a Table Note- Very important title
The Number of Kids per household of parents years old
Number of households
Percent
0 children
8481
15.6
1 child
17071
31.4
2 children
23268
42.8
3 children
4621
8.5
4 plus children
924
1.7
Total
54365
100

4. Graphs used to organize data
Pie charts – used when looking at a fraction of a whole – equals 100%- qualitative or categorical data
Bar Graphs- used when data points are few. Used with qualitative data /DV-numerical/IV non-numerical
Line Graph- used when you have 2-3 variables, experimental results-quantitative data /IV and DV are both numerical

5. Pie Charts – use when working with percents
Used for Categorical or qualitative Variables – looking at a fraction of a whole
To make a pie chart, first draw a circle. The circle represent a whole. Wedges within the circle represent the parts. The angle spanned by each wedge is in proportion to the size of that part.
For instance, If we were displaying the amount of education people have had and 21.3% had a bachelor’s degree we would make that slice 77 wide.
0.213  360 = 77

6. Example – Pie chart
Pie Chart – showing the number of children found per household

7. Bar Graphs Use for Categorical or qualitative Variables
The height of the bars show the percent of each category
The width of the bars need to be the same

8. Example - Bar Graphs
Bar Graph- showing number of children per household
Number of houses
Number of children

9. Pie chart
Only compare parts of a whole
are often hard to read since it is difficult to compare the angles of the different pieces of the pie
Bar graphs
can compare quantities that are not parts of a whole
Easier to interpret than a pie chart

10. Line Graph- shows trends, dramatic changes or patterns
A line graph is used for graphing quantitative variables that change over time
Ex: bank account over time, water levels over time, and performance of stocks
Put time (IV) on the horizontal scale( x axis) and the variable you are measuring (DV) on the vertical scale
( y axis)
Use with many data points, May have more than 1 variable (line)
Connect the data points by lines to display the change over time

11. Example - Line Graph

12. Making good graphs Label the x and y axes
Tell which units you used for your variables
X axis is independent variable/ Y axis is dependent variable
Title of Graph – dependent variable vs independent variable