Lab topics, February 13, 2001


  1. Remaining questions on Quiz 2 taken 2/6/02.

  2. Transformations of data
    1. A guide to plotting log-transformed data on their original scale
      1. log(y): Breakdown time of insulating fluid.
      2. log(x): Meat processing data
      3. log(x),log(y): Island area and number of species

    2. Problem 17 of Chapter 8. Data in ragwort.txt

      1. Read in data.

      2. Using "Data" - "Transform", create these new variables: sqrt(mass), sqrt(load), log(mass), log(load).

      3. Produce a pairs plot of all pairs of X's and Y's. Under "Graph" - "2D Plot", choose "Plot Type" "Scatter Plot Matrix". Shift click for all relevant X's (load, log(load) and sqrt(load)), and all relevant Y's.

      4. Which two plots show a linear relationship between load and mass variables?

      5. For the best two models selected above, plot residuals vs. fitted values, and choose the best fitting model. Does your model also offer ease of interpretation? Interpret the slope parameter in a sentence.

    3. Crab claw size and force, Problem 8 under Practice problems for Midterm Exam.

  3. Exploratory data analysis. Pairs plots in Splus. Mammal brain size data, Case Study 2 in Chapter 9. Which variables appear to be explain the variability in brain weight? Are transformations needed here?