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Homework 2

Due date: October 27, 2015.

  1. Use the data in
    http://www.utdallas.edu/~ammann/stat3355scripts/BirthwtSmoke.csv
    a.
    Construct a 95% confidence interval for the proportion of mothers who smoke.
    b.
    What sample size would be required to estimate this proportion to within 0.02 of the population proportion with 95% confidence if no prior bounds are used. What is this sample size if the sample proportion from part a is used as the prior bound?
    c.
    Construct a 95% confidence interval for the mean birth weight of newborns with mothers who smoke. Do the same for mothers who don't smoke.
    d.
    Use this data as a preliminary sample to determine the sample size required to estimate the mean birth weight for mothers who smoke to within 0.4 with 99% confidence. Do the same for mothers who don't smoke.
    e.
    Construct a 90% confidence interval for the s.d. of birth weight for mothers who smoke. Do the same for mothers who don't smoke.

  2. Use the data in
    http://www.utdallas.edu/~ammann/stat3355scripts/crabs.txt
    a.
    There are 4 combinations of species and sex (B-M, B-F, O-M, O-F) for the crabs in this data. Construct separate 95% confidence intervals for mean FL for each of these groups. Repeat for each of the other measurements, RW, CL, CW, BD.
    b.
    Construct separate 90% confidence intervals for the s.d. of FL for each of these groups. Repeat for each of the other measurements, RW, CL, CW, BD.
    c.
    Construct a plot of RW versus CW using different colors for the two species and different plot symbols for Male and Female. Include a legend in the plot that shows which colors go with which species and which symbol goes with which sex.
    d.
    Obtain separate correlation coefficients between RW and CW for each of the 4 combinations of species and sex. Compare these correlations to the overall correlation between RW and BD using all crabs. Interpret these correlation coefficients.
    e.
    Construct 4 separate plots of RW vs CW corresponding to each of the 4 combinations of species and sex. Superimpose on each plot 2 regression lines: one which represents the regression line to predict RW based on CW using only the combination of species and sex in the plot and the other which represents the regression line to predict RW based on CW for all crabs. Put these 4 plots on the same page.


next up previous
Next: Homework 3 Up: Homework and Project Assignments Previous: Homework 1
Larry Ammann
2015-12-03