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Describing Data

Describing Data . Charts and Graphs. Lecture Objectives. You should be able to: Define Basic Terms Recognize Types of Data and Data Scales Draw appropriate graphs based on type of data and type of analysis desired. Interpret the graphs. Basic Terms. Data, Information, and Knowledge

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Describing Data

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  1. Describing Data Charts and Graphs

  2. Lecture Objectives • You should be able to: • Define Basic Terms • Recognize Types of Data and Data Scales • Draw appropriate graphs based on type of data and type of analysis desired. • Interpret the graphs

  3. Basic Terms • Data, Information, and Knowledge • Populations and Samples • Variables and Observations • Types of Data: • Categorical and Numerical • Cross Sectional and Time Ordered

  4. Data Data Data Data, Information, and Knowledge Knowledge Information • Processing • Analysis • Reports • Application • Meaning • Relevance

  5. Populations and Samples Population: Collection of all possible entities of interest Described by Parameters Sample: Subset of collection Described by Statistics Statistical Inference Art and science of using samples to make conclusions about populations.

  6. Variables and Observations VARIABLES OBSERVATIONS Measurement

  7. Types of Data: Categorical and Numerical Categorical Numerical

  8. Data Scales Data are generally classified into four types: • Nominal – Categorical data • Ordinal – shows ranks, intervals may vary • Interval – intervals are constant, arbitrary 0 • Ratio – Numeric data with a ‘real’ 0 value. Ordinal, Interval and Ratio scales are all Numeric data.

  9. Types of Data: Time Series and Cross-sectional Variable(s) at one point in time across multiple entities (countries in this case) Variable(s) over time

  10. Numeric Data (Interval or Ratio): Frequency Tables A Frequency Table showing a classification of the AGE of attendees at an event.

  11. Frequency Histograms A graphical display of distribution of frequencies

  12. Developing Frequency Tables and Histograms • Sort Raw Data in Ascending Order: • 12, 13, 17, 21, 24, 24, 26, 27, 27, 30, 32, 35, • 37, 38, 41, 43, 44, 46, 53, 58 • Find Range: 58 - 12 = 46 • Select Number of Classes: 5 (usually between 5 and 15) • Compute Class Interval (width): 10 (range/classes = 46/5 then round up) • Determine Class Boundaries (limits): 10, 20, 30, 40, 50 • Compute Class Midpoints: 15, 25, 35, 45, 55 • Count Observations & Assign to Classes

  13. Categorical Data:Bar Charts

  14. Categorical Data:Pie Charts

  15. Numeric Data by Category

  16. Bivariate Numerical DataScatter Plot

  17. Two variables, different units Source: http://www.epa.gov/ttn/chief/trends/trends06/nationaltier1upto2006basedon2002finalv2.1.xls

  18. Chapter Summary Categorization: Bar, Pie charts Distribution: Stem and Leaf, Histogram, Box Plot Relationships: Scatter Plots, Line Charts Multivariate: Spider Plots, Maps, Bubble Charts

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