Oil spill impact on seabirds. The Journal of Agricultural, Biological, and Environmental Statistics (Sept. 2000) published a study on the impact of the Exxon Valdez tanker oil spill on the seabird population in Prince William Sound, Alaska. Data were collected on 96 shoreline locations

(called transects) of constant width, but variable length. For each transect, the number of seabirds found is recorded, as are the length (in kilometers) of the transect and whether

or not the transect was in an oiled area. (The first five and last five observations in the EVOS file are listed in the accompanying table.)
Transect Seabirds Length Oil 1 0 4.06 No 2 0 6.51 No 3 54 6.76 No 4 0 4.26 No 5 14 3.59 No f f f f 92 7 3.40 Yes 93 4 6.67 Yes 94 0 3.29 Yes 95 0 6.22 Yes 96 27 8.94 Yes

a. Identify the variables measured as quantitative or qualitative.

b. Identify the experimental unit.

c. Use a pie chart to describe the percentage of transects in oiled and unoiled areas.

d. Use a graphical method to examine the relationship between observed number of seabirds and transect length.

e. Observed seabird density is defined as observed count divided by length of transect. MINITAB descriptive statistics for seabird densities in unoiled and oiled transects are displayed in the printout at the top of the page. Assess whether the distribution of seabird densities differs for transects in oiled and unoiled areas.

f. For unoiled transects, give an interval of values that is likely to contain at least 75% of the seabird densities.
g. For oiled transects, give an interval of values that is likely to contain at least 75% of the seabird densities.
h. Which type of transect, an oiled or unoiled one, is more likely to have a seabird density of 16? Explain.

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Descriptive Statistics: Density Variable Oil N Mean StDev Density no 36 3.27 6.70 5.968 yes 60 3.495 Minimum Q1 Median Q3 Maximum 0.000 0.000 0.890 3.87 36.23 0.0000 0.000 0.700 5.233 32.836