Question

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求救 統計 #8 （可支薪）

8. The NBI data were analyzed and the results made available at the FHWA Web site. Using the
FHWA inspection ratings, each of the 608,272 highway bridges in the US was categorized as
structural deficient, functionally obsolete, or safe. About 13.5% of the bridges were found to be
structural deficient, while 3.5% were functionally obsolete.
a. What is the variable of interest to the researchers?
b. Is the variable of part a quantitative or qualitative?
c. Is the data set analyzed a population or a sample? Explain.
d. How did the NBI obtain the data for the study?