# Question: The article Odds Are It s Wrong Science News March 27

The article “Odds Are, It’s Wrong” (Science News, March 27, 2010) poses the following scenario: Suppose that a test for steroid use among baseball players is 95% accurate—that is, it correctly identifies actual steroid users 95% of the time, and misidentifies non-users as users = percent of the time. . . . Now suppose, based on previous testing, that experts have established that about = percent of professional baseball players use steroids. Answer the following questions for this scenario.

a. If 400 professional baseball players are selected at random, how many would you expect to be steroid users and how many would you expect to be non-users?

b. How many of the steroid users would you expect to test positive for steroid use?

c. How many of the players who do not use steroids would you expect to test positive for steroid use (a false positive)?

d. Use your answers to Parts (b) and (c) to estimate the proportion of those who test positive for steroid use who actually do use steroids.

e. Write a few sentences explaining why, in this scenario, the proportion of those who test positive for steroid use who actually use steroids is not .95.

a. If 400 professional baseball players are selected at random, how many would you expect to be steroid users and how many would you expect to be non-users?

b. How many of the steroid users would you expect to test positive for steroid use?

c. How many of the players who do not use steroids would you expect to test positive for steroid use (a false positive)?

d. Use your answers to Parts (b) and (c) to estimate the proportion of those who test positive for steroid use who actually do use steroids.

e. Write a few sentences explaining why, in this scenario, the proportion of those who test positive for steroid use who actually use steroids is not .95.

## Answer to relevant Questions

The press release “Luxury or Necessity? The Public Makes a U-Turn” (Pew Research Center, April 23, 2009) summarizes results from a survey of a nationally representative sample of n = 1003 adult Americans. a. One question ...A simple linear regression model was used to describe the relationship between y = hardness of molded plastic and x = amount of time elapsed since the end of the molding process. Summary quantities included n 5 15, SSResid = ...An experiment to study the relationship between x = time spent exercising (minutes) and y 5 amount of oxygen consumed during the exercise period resulted in the following summary statistics. a. Estimate the slope and y ...Consider the accompanying data on x = research and development expenditure (thousands of dollars) and y = growth rate (% per year) for eight different industries. a. Would a simple linear regression model provide useful ...An investigation of the relationship between x = traffic flow (thousands of cars per 24 hours) and y 5 lead content of bark on trees near the highway (mg/g dry weight) yielded the accompanying data. A simple linear ...Post your question