Question

The US Department of Transportation (DOT) is tasked with maintaining the nation's 615,322 bridges. The US DOT believes the percentage of structurally deficient bridges is below 10%. A private civil engineering group found 11.9% of the 15,126 bridges it studied were, in fact, structurally deficient. a. What is the population of interest? b. What is the sample? c. The number 11.9% represents a _______________ . d. The number 615,322 represents a _______________. d. To state that "11.9 % of all U.S. bridges are structually deficient" represents a form of ___________ statistics. e. Would it be reasonable to conclude that 11.9% of all U.S. bridges are structually deficient? What considerations should be made before making such a claim?

Answer 1

Answer a)

Populaiton of interest is nation's 615,322 bridges.

Answer b)

The sample is 15,126 bridges studies by a private civil engineering group.

Answer c)

The number 11.9% represents a percentage of of structurally deficient bridges in the sample.

Answer d)

To state that "11.9 % of all U.S. bridges are structually deficient" represents a form of inferential statistics.

Answer e)

No, it is not resonable to conclude that 11.9% of all U.S. bridges are structually deficient. Before making such claim it is improtant to consider following points:

1. Sampling - There is no infomration given as to how a private civil engineering group selected bridges. If sampling done by a private civil engineering group is biased then there are chances of claim being wrong.

2. Confidence Level - Sample size selected should be as per confidence level required. The confidence level tells you how sure you can be. It is expressed as a percentage and represents how often the true percentage of the population who would pick an answer lies within the confidence interval. The 95% confidence level means you can be 95% certain; the 99% confidence level means you can be 99% certain. Most researchers use the 95% confidence level. At present, it is not stated at what confidence level claim is made.

After taking into account above points, it is important to conduct hypothesis testing for one population proportion (p).