More%20about%20Correlations

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More about Correlations
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Spearman Rank order correlation

• Does the same type of analysis as a Pearson r but
  with data that only represents order.
• Ordinal data represents highest to lowest but
  without any indication of distance between ranks.

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Spearman correlation cont.

• With a Spearmen rank order correlation both
  variables (x and y) are ranked.
• The correlation then determines the relationship
  between rankings
• Easier calculation but less powerful as a
  statistical test.

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Multiple Regression

• Correlation Relationship between two variables.
• Regression What would you predict about the
  dependent variable, given the independent
  variable(s).

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• Since you can have several variables
• One or more are designated as dependent while all
  others are independent.
• The DV is identified based on prior knowledge or
  expectations.
• The IVs can be continuous measurements
  (different than an ANOVA)
• This analysis still does not show causation.

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Relationship is defined by

• Where
• a is the intercept
• Each x is an IV
• Each B is a regression coefficient for a
  particular IV

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Looking at the output

• Correlation overall is evaluated with F.

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IV1
IV2
DV
IV3
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• R - Multiple correlation coefficient is the
  measure of correlation between the predicted y
  and the obtained y.
• R2 - the portion of the variation of the DV that
  is predictable from the regression equation.

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Output cont.

• Each IV can be evaluated based on a t test based
  on the regression coefficients.

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• If
• cancer deaths
• of smokers and
• of the population over 75
• are used to predict median health care costs

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If

• of hospitals and
• of MDs
• Are used to predict median health care costs

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