AP Statistics · Topic 9.5

Carrying Out a Test for the Slope of a Regression Model Practice

Part of Inference for Quantitative Data: Slopes.(VAR-7.F)

Practice questions

17

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Sample questions

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  1. Sample 1difficulty 1/5

    A simple linear regression is fit on n = 30 observations.

    Simple Linear Regression n = 30 observations df for slope = ?

    What is df for the t-test on slope?

    • A

      27

    • B

      29

    • C

      30

    • D

      28

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    Why

    df = n - 2 = 30 - 2 = 28 (estimating intercept and slope).

  2. Sample 2difficulty 2/5

    A regression output reports residual df = 17.

    Residual df = 17 What was n?

    What is the sample size n?

    • A

      18

    • B

      20

    • C

      19

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    • D

      17

    Why

    df = n - 2, so n = df + 2 = 17 + 2 = 19.

  3. Sample 3difficulty 2/5

    A regression of weekly sales (y, in thousands) on advertising spend (x) gives the output below.

    Regression Output Predictor Coef SE t Constant x 12.5 3.2 3.91 2.4 0.5 4.80 n = 20, R-sq = 0.56, s = 4.2

    What is the estimated slope?

    • A

      4.80

    • B

      12.5

    • C

      2.4

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    • D

      0.5

    Why

    The slope is the coefficient on x: 2.4. The constant 12.5 is the intercept.

  4. Sample 4difficulty 2/5

    The same regression output is shown with slope estimate 2.4 and SE = 0.5.

    Regression Output Predictor Coef SE t x 2.4 0.5 4.80 n = 20

    What is the t-statistic for testing H0: beta = 0?

    • A

      4.80

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    • B

      12.50

    • C

      2.40

    • D

      0.50

    Why

    t = (b - 0)/SE(b) = 2.4/0.5 = 4.80, as shown.

  5. Sample 5difficulty 2/5

    Computer output shows slope = 4.2 with SE = 1.4, n = 30.

    Regression Output Coef SE t 4.2 1.4 ?

    What is the t-statistic?

    • A

      3.0

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    • B

      5.6

    • C

      1.4

    • D

      2.5

    Why

    t = b / SE(b) = 4.2 / 1.4 = 3.0.