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Chapter 3 Displaying Data Tables and Graphing

Chapter 3 Displaying Data Tables and Graphing. The Value of Charts. Visual learners will understand concepts and data more easily if they are portrayed graphically. There are many commonly used graphical techniques used in statistics.

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Chapter 3 Displaying Data Tables and Graphing

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  1. Chapter 3Displaying DataTables and Graphing

  2. The Value of Charts Visual learners will understand concepts and data more easily if they are portrayed graphically. There are many commonly used graphical techniques used in statistics. Quantitative people may prefer to look at the numeric data. They may prefer to look at data tables and spreadsheets.

  3. Frequency Distributions Organized in table form. Data Value Frequency

  4. Frequency Distributions cont’d If there is a lot of data then breaking it into Class Intervals may be helpful. Intervals must cover the entire range of data Intervals should not overlap Intervals should all be of the same length

  5. Example Frequency Distribution using Class Intervals Class Interval Midpoint Frequency 10 – 14 12 5 15- 19 17 12 20-24 9 8

  6. Cumulative Freq Distributions Can accumulate Frequencies and also %Frequency, see Table 3.15, page 46 Score Freq %Freq Cum Freq %Cum freq 20 3 20 3 20 25 5 33 8 53 30 7 47 15 100 The Cumulative Frequency Percent is the Percentile.

  7. Graphical Display Tools Histograms use vertical bars to represent frequencies. These can be made for discrete data values or for class intervals. The bars adjoin each other. Vertical axis is always frequency Horizontal axis represents data values or class intervals

  8. Histograma bar chart for quantitative data 1 2 3 4 5

  9. Frequency Polygon 1 2 3 4 5

  10. Histograms and Freq Polygons Both can be done cumulatively. Both can be done for discrete or class interval data Both convey the same information. Choice is a matter of personal preference. A cumulative frequency polygon is also called an S-curve or Ogive.

  11. Ogive 100 80 60 Cumulative Percent Frequency 40 20 Scores 50 60 70 80 90 100 110

  12. Histograms and Freq Polygons Can overlay two Frequency Polygons on the same axis for comparison. With either x-axis is normally an Interval or Ratio scale Underlying variable may be discrete or continuous but as usual we approximate using discrete values.

  13. Pie Charts APA Recommends 4 or 5 wedges. Up to 7 is quite common. Pie pieces represent non-overlapping categories Can label pie pieces with data values and/or percent of total.

  14. Bar Graphs Can be used for non-quantitative or quantitative data. See Histograms. Bars normally do not touch by convention X-axis scale is usually just a nominal scale Can be drawn with bars vertical or horizontal Can use joint bars to represent two groups being compared

  15. Line Graphs Convenient way to compare two or more groups. Not a Frequency Polygon X-axis is normally a nominal scale

  16. End of Show

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