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Graphs, Good and Bad

Graphs, Good and Bad. 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.

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Graphs, Good and Bad

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  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 25-35 years old

  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

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