The Shanghai Women’s Health Study (SWHS) was under-taken to determine risk factor for different cancers among Asian women. The women were recruited from urban communities in 1997-2000 and were interviewed every 2 years to obtain health-related information. One issue is whether risk prediction models derived from American populations are also applicable to Asian women. Suppose the expected number of breast cancer cases among a large number of 45-to 49-year-old women in this study who were followed for 7 years is 149, while the observed number of cases is 117. Are there an unusual small number of cases among Asian women? Why or Why not?
Continuous Probability Distributions
Probability distributions are of two types, which are continuous probability distributions and discrete probability distributions. A continuous probability distribution contains an infinite number of values. For example, if time is infinite: you could count from 0 to a trillion seconds, billion seconds, so on indefinitely. A discrete probability distribution consists of only a countable set of possible values.
Normal Distribution
Suppose we had to design a bathroom weighing scale, how would we decide what should be the range of the weighing machine? Would we take the highest recorded human weight in history and use that as the upper limit for our weighing scale? This may not be a great idea as the sensitivity of the scale would get reduced if the range is too large. At the same time, if we keep the upper limit too low, it may not be usable for a large percentage of the population!
The Shanghai Women’s Health Study (SWHS) was under-taken to determine risk factor for different cancers among Asian women. The women were recruited from urban communities in 1997-2000 and were interviewed every 2 years to obtain health-related information. One issue is whether risk prediction models derived from American populations are also applicable to Asian women. Suppose the expected number of breast cancer cases among a large number of 45-to 49-year-old women in this study who were followed for 7 years is 149, while the observed number of cases is 117. Are there an unusual small number of cases among Asian women? Why or Why not?
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