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# Graphs, Good and Bad - PowerPoint PPT Presentation

Graphs, Good and Bad MA155 Chapter 10 Organizing Data The first step in data analysis is to display the data in a graph. Look first for the overall pattern in the data, and then for striking exceptions to that pattern.

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MA155

Chapter 10

### Organizing Data

• The first step in data analysis is to display the data in a graph.

• Look first for the overall pattern in the data, and then for striking exceptions to that pattern.

• After looking at the graphs, you can use well-chosen numerical descriptions.

### Describing Distributions

• Distributions

• The distribution of a variable tells us what value the variable takes and how often each value occurs.

### Data Tables

• Clearly Labeled

• Units are stated

• Source of Data

### Pie Charts

• A whole is divided into parts

• Steps

• Draw a circle

• Make wedges that are representative of the proportion

• The parts do make a whole

### Bar Graph

• The height of each bar shows the proportion

• It clearly shows the results

• They are easy to make

### Bar Graph

Categorical Variable

Places an individual into one of several groups or categories

Quantitative Variable

Takes numerical values for which arithmetic operations make sense

### Categorical Examples

• Race

• Sex

• Employment Status

• Hair Color

• Type of Car

### Quantitative Examples

• Measurements made on scales of equal units

• Examples

• Height in inches

• Reaction time in seconds

• Temperature in degrees Celsius

### Remember

• Not all numbers carry the same information

• Luke is a skateboarder.

• Luke finished first at the 2000 Gravity Games

• Luke scored a 92.60 on the street course.

• The scale of measurement depends on the measuring process, not on the property measured.

### Displaying Distributions

• To display the distribution of a variable measured in a nominal scale, use a pie chart or a bar graph

• Pie charts emphasize how individual counts or percents are related to the whole

• Bar graphs emphasize how quantities compare with one another.

• Use pie charts and bar graphs when displaying the distribution of categorical variables.

### Pictograms

Source: http://www.usatoday.com

### Line Graphs

• Show the behavior of a variable over time

• Horizontal Axis Time

• Vertical AxisScale of Variable

### Scales

• The scales of a line graph can cause a graph to be misleading

### Making Good Graphs

• Must be clearly labeled

• Units stated

• Source of Data

• Make the data stand out!