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![]() Fall Semester 2003 |
Chapter 4: Describing Your Data.
Chapter 5: Probability Distributions
During World War II many economists, mathematicians, and statisticians were members of Columbia University's Statistics Research Group, which did
high-level consulting work for the armed services.
As part of this group's work, statistician Abraham Wald was asked where to place armor on planes. It seemed obvious to the aircraft engineers that armor was
needed at the places most frequently hit, as found in a large sample of battle-proven airplanes. After studying the bullet holes of a sample of returning
planes, Wald's conclusion was to place the armor where bullet holes were least frequently found in these planes, and that's what he recommended.
Now the questions:
Part of the challenge in statistics is to remove all bias from sampling. This is difficult to do and subtle biases can creep into even the most carefully designed studies. Here's another problem:
ABC's 20/20 television broadcast on July 16, 1993 reported on a study in which individuals who had lived to be 100 years of age or more were queried in the hope of finding common characteristics. The implication was drawn that if a younger person worked at acquiring the characteristics shared by these centenarians, then the probability of reaching such an old age increased. Why was this study design inappropriate for the implication drawn?
NORMDIST(40, 50, 4, TRUE)
calculate?
NORMDIST(40, 50, 4, FALSE)
calculate?
NORMINV(0.90, 50, 4)
calculate?
A113