Graphs Good and Bad Two types of variables

Graphs, Good and Bad

Two types of variables l Categorical variables- places individuals into one of categories or groups ¡ l 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.

Starting with a Table l Note- Very important title l The Number of Kids per household of parents 25 -35 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

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

Pie Charts – use when working with percents Used for Categorical or qualitative Variables – looking at a fraction of a whole l 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. l 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 ¡

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

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

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

l 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 ¡ l Bar graphs ¡ can compare quantities that are not parts of a whole ¡ Easier to interpret than a pie chart

Line Graph- shows trends, dramatic changes or patterns l 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 l ( y axis) l Use with many data points, May have more than 1 variable (line) l Connect the data points by lines to display the change over time l

Example - Line Graph

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