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Chapter 1

STA 200 Summer I 2011. Chapter 1. Individuals and Variables. Individuals : Variables : A variable can take different values for different individuals. Highest Tuition, 2010-11 (U.S. colleges). The variables are:

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Chapter 1

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  1. STA 200 Summer I 2011 Chapter 1

  2. Individuals and Variables • Individuals: • Variables: A variable can take different values for different individuals.

  3. Highest Tuition, 2010-11 (U.S. colleges) The variables are: (Note about Total Cost: 5 over $50K in 2008-09, 58 over $50K in 2009-10, 100 over $50K in 2010-11 (including one public school))

  4. Observational Study vs. Experiment • Observational Study: • passive data collection • Observe and record, but don’t interfere. • Experiment: • active data production • Treatments are imposed on individuals in order to observe their effects.

  5. Example: Plastic Window Insulation • Putting plastic insulation over one’s windows is thought to reduce the amount of heat loss during the wintertime. • Consequently, the heating bill is thought to be reduced as well. • Suppose this phenomenon is to be studied in an apartment complex.

  6. Observational Study • Each tenant chooses whether or not to cover their windows with plastic insulation. • Each month, the meter readings/heating bills are recorded for each apartment: those with plastic insulation, and those without. • The meter readings/heating bills of the two groups are compared.

  7. Experiment • Half of the apartments are randomly selected. These apartments will use plastic insulation on their windows; the other half will not. • Each month, the meter readings/heating bills are recorded for each apartment: those with plastic insulation, and those without. • The meter readings/heating bills of the two groups are compared.

  8. Sample Surveys • Sample Survey: • Population: • Sample: • Census:

  9. Example: Health Insurance • The Gallup Organization conducted a poll in November 2010 that asked, among other things, “Do you have employer-based health coverage?” • Gallup reported that the results were based on telephone interviews with a random sample of 27,218 adults living in the United States. • What is the population? • What is the sample?

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