Midterm Exam sample questions

Psychology 2812B FW23

Multiple Choice (1 pt each)

  1. To grab certain rows of a data tibble, we can use the following dplyr command:
    1. filter()
    2. select()
    3. slice()
    4. arrange()
  1. In the figure shown below, there is a ______ correlation between X and Y:
    1. positive
    2. negative
    3. zero
    4. none of the above

  1. In multiple regression, variance inflation factors (VIFs) are a measure of:
    1. the influence of a single observation on heteroscedasticity
    2. whether or not the predictors are too highly correlated with each other
    3. the variance of the residuals
    4. the influence of a single observation on the estimate of the regression line
  1. In linear regression the line of best fit is found by:
    1. minimizing the sum of squared errors
    2. minimizing the sum of the residuals
    3. minimizing the slope and intercept of the regression line
    4. minimizing the sum of absolute errors
  1. In multiple regression with two predictor variables X_{1} and X_{2} we estimate:
    1. two slopes and two intercepts
    2. one slope and two intercepts
    3. two slopes and one intercept
    4. one slope and one intercept

Short Answer (2 pts each)

  1. Jessie estimates a linear regression model to predict monthly spending on groceries (y) from monthly income (x). They find that the estimated regression equation is y = 0.5 + 0.2x and that the p-value for the slope is p=0.02. What does the slope coefficient 0.2 mean? What does the p-value 0.02 mean?

  2. Explain why one might prefer to describe the goodness of fit of a regression model using the standard error of the estimate s_{est} instead of r^{2}.

Long Answer (5 pts each)

  1. Ripley esimates a multiple linear regression model to predict credit card spending (Y) from monthly income (X_{1}), age (X_{2}), and number of children (X_{3}). They find that the estimated regression equation is Y = 100 + 0.2X_{1} + 0.1X_{2} - 0.5X_{3}. Describe the steps you would take to refine the model and explain the rationale for each step.