StatTutor Lesson - Facts about correlation

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Facts about correlation
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      Question 1

      42

      Question 1.

      True or false: The sign on r always denotes the direction of the relationship.

      		A.
      		B.
      Correct. This is a correct statement.
      Incorrect. This is a correct statement.
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      Question 2

      77

      Question 2.

      True or false: A value of r = –1.5 has to be an error.

      		A.
      		B.
      Correct. This is a correct statement.
      Incorrect. This is a correct statement.
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      Questions 3-4

      157

      Question 3.

      If we change the unit of measure for X from centimeters to feet, will the value of r change?

      		A.
      		B.
      Correct. Changing the unit of measure for X or Y does not change “r” because “r” is computed using z-scores which have no unit of measure.
      Incorrect. Changing the unit of measure for X or Y does not change “r” because “r” is computed using z-scores which have no unit of measure.
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      Question 5

      207

      Question 5.

      Scatterplot image

      True or false: Computing r as a measure of the relationship between X and Y is misleading for the data in the above scatterplot.

      		A.
      		B.
      Correct. “r” should only be computed when the relationship between X and Y is linear; when the relationship is not linear, “r” is misleading.
      Incorrect. “r” should only be computed when the relationship between X and Y is linear; when the relationship is not linear, “r” is misleading.
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      Question 6

      243

      Question 6.

      True or false: r is resistant to outliers.

      		A.
      		B.
      Correct. An outlier can either pull r closer to +1.0, –1.0 or 0.0 depending on where the outlier is relative to the other data.
      Incorrect. An outlier can either pull r closer to +1.0, –1.0 or 0.0 depending on where the outlier is relative to the other data.
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      Question 7

      298

      Question 7.

      Suppose someone claims a strong correlation between salary and gender. What should you conclude?

      		A.
      		B.
      		C.
      Correct. “r” is computed from bivariate quantitative data. You should never compute “r” with categorical data. In this claim, correlation may not have been computed, but rather the term “correlation” is used incorrectly.
      Incorrect. “r” is computed from bivariate quantitative data. You should never compute “r” with categorical data. In this claim, correlation may not have been computed, but rather the term “correlation” is used incorrectly.
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