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Focus on graphs for describing data, with a quick overview of central tendency and variability

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- 1. Descriptive Statistics<br />PSY 330 Research Methods<br />
- 2. Measurements Choices Determine Analysis Options<br />Choice of measure occurs in research design<br />Measures yield data at a particular scale (level) of measurement (Nominal, Ordinal, Interval, Ratio)<br />Interval or Ratio data can be “recoded” to create groups (e.g., age groups, income ranges)<br />Grouped data cannot be expanded to create Interval or Ratio data <br />Scale (Level) of Measurement determines which techniques are appropriate.<br />
- 3. Matching Average to Data<br />
- 4. Matching Variability Measure to Data<br />Range and Interquartile Range (IQR) use only a few scores.<br />Standard deviation and variance use the value of each score in the data set<br />Range and IQR are related to Median<br />Standard Deviation and Variance are related to the Mean.<br />
- 5. Purpose of a Graph<br />A visual presentation of data<br />Relationships & comparisons are visual<br />Less daunting to some than tables of numbers<br />Allows some artistry and creativity<br />Accuracy is important<br />Characteristics of data <br />Measurement choices in design determine analysis choices later<br />Scale (level) of measurement determines which graphs can be used<br />Nature of the particular data set is also important<br />
- 6. Graphs for Complex Data<br />The Future of Food. (2008) WiredMagazine 16:11<br />From ChoiceRanker website via JunkCharts blog at http://junkcharts.typepad.com/junk_charts/2008/07/its-raining-colors-here-too.html<br />
- 7. Basic requirements for graphs<br /><ul><li>Axes drawn and labeled
- 8. Category values labeled
- 9. Title for graph
- 10. Data bars proportional to number of cases in data
- 11. Balanced
- 12. Maintains scale
- 13. No “chart junk”
- 14. Not complicated
- 15. Does not convey too much</li></li></ul><li>Graphs for Discrete Data(counts)<br />Data are in categories<br />Nominal <br />Ordinal (if few categories)<br />Types of graph:<br />Pie Chart<br />Bar Chart or Pictograph (Excel: Column chart)<br />Show the Frequency (count) or Percent<br />
- 16. BAR CHART: the Good<br />Area of bars combined is 100%<br />Area of each bar is proportional to its percent of total<br />Bars do not touchbecause categoriesare discrete.<br />Many variations; this is the most simple.<br />
- 17. The Bad:design dominatestrends or data<br />
- 18. PICTOGRAPH: the Good bars constructed of equal size pictures<br />
- 19. PICTOGRAPH: the Ugly<br />Elements of unequal size<br />Just heads of some kids<br />All children are playing except those from China – subtle racism<br />
- 20. BAR CHART – problems to consider:area, color – & why is that jogger there?<br />
- 21. PIE CHART: the Good<br />Area of pie = 100%<br />Wedge is proportional to percentage of cases<br />Labels show count or percent <br />Ten slices is the maximumto remain clear<br />
- 22. PIE CHART: the Badcharts confuse or obscure the pattern in the data<br />
- 23. Graphs for Continuous Data (sometimes Ordinal)<br />Graph shows continuity of the construct<br />Histogram: bars that touch at real limits<br />Line graph: covers range (a.k.a. Frequency Polygon)<br />Horizontal axis goes from low to high<br />Intervals shown for Interval or Ratio data<br />Some ordinal data also graphed this way(e.g., strongly agree, agree, slightly agree, etc)<br />
- 24. HISTOGRAM: the Good<br />Bar width is a rangeof scores or the reallimits of scores.<br />Ranges equal width<br />Labels show mid-point or real limits<br />Low scores on left, high scores on right<br />
- 25. HISTOGRAM: the Bad<br />Ranges of data<br />Unequal<br />Indeterminate<br />Spacing of “bars” is unequal.<br />Water, sky, umbrellaall detract from graph<br />
- 26. Line Graphs / Frequency Polygon<br />Same requirements as histogram.<br />If more than one line,legend or labels are needed.<br />More than four or fivelines can be hard tointerpret<br />from SRB Documentary. (2008). Demographic Winter: the Decline of the Human Family at http://www.demographicwinter.com/index.html<br />
- 27. LINE GRAPH: the Bad<br />Why is the headline “Steady growth” for this graph?<br />Hint: check the axis values<br />If it is growth, is it steady ?<br />Hint: how did each of the three variables change from 1988 to 1989.<br />
- 28. Interesting trends in graphs:Population Map Area=population, displayed by location. <br />
- 29. World Mapper ProjectA collection of world maps, where territories are re-sized according to the subject of interest.<br />Internet Users in 2002<br />
- 30. World Mapper Projecthttp://www.worldmapper.org/<br />Alcohol Consumption 2006<br />
- 31. Descriptive Statistics<br />PSY 330 Research Methods<br />

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