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Important to distinguish between regression and correlation

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Objective: To describe the dependence of variable Y on the independent variable X ... samples of Recent marine mud in Louisiana. Estuary (a small inlet on the ... – PowerPoint PPT presentation

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Title: Important to distinguish between regression and correlation


1
Important to distinguish betweenregression and
correlation
  • Regression
  • Objective To describe the dependence of
    variable Y on the independent variable X
  • Correlation
  • Objective To examine if two variables are
    interdependent or if they covary

2
Example regression
  • Background Moisture content of core
  • samples of Recent marine mud in Louisiana
  • Estuary (a small inlet on the Gulf Coast) was
  • measured immediately after it was removed
  • from the core barrel (after forced drying).

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Example correlation
  • Length and width of shells of the a brachiopod
  • (lamp shell) species
  • Question Does length covary with width?

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Simple linear regression
  • We want to express a variable (dependent or
  • response) and as a linear function of another
  • variable (independent or regressor).

8
Cotton example
  • Cotton is particularly sensitive to rainfall. Dry
    weather in June appears to slow growth.
  • The following data are records from an
  • agricultural experiment station

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  • June rainfall (mm) Yield (lb/acre)
  • 3 1120
  • 6 1750
  • 7 1940
  • 9 2130
  • 11 2380
  • 15 2650
  • 17 2990
  • 19 3130

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  • Yield is the response variable
  • Rainfall in June is the regressor
  • Denote Yield as Y and Rainfall as X.

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