Problem

Language impairment in children. Children who develop unexpected difficulties with the spo...

Language impairment in children. Children who develop unexpected difficulties with the spoken language are often diagnosed as specifically language impaired (SLI). A study published in the Journal of Speech, Language, and Hearing Research (Dec. 1997) investigated the incidence of SLI in kindergarten children. As an initial screen, each in a national sample of over 7,000 children was given a test for language performance. The percentages of children who passed and failed the screen were 73.8% and 26.2%, respectively. All children who failed the screen were tested clinically for SLI. About one-third of those who passed the screen were randomly selected and also tested for SLI. The percentage of children diagnosed with SLI in the “failed screen” group was 20.5%; the percentage diagnosed with SLI in the “pass screen” group was 2.8%.

a. For this problem, let “pass” represent a child who passed the language performance screen, “fail” represent a child who failed the screen, and “SLI” represent a child diagnosed with SLI. Now find each of the following probabilities: P(Pass), P(Fail), P(SLI | Pass), and P(SLI | Fail).


b. Use the probabilities from part a to find P(Pass ∩ SLI) and P(Fail ∩ SLI). What probability law did you use to calculate these probabilities?


c. Use the probabilities from part b to find P(SLI). What probability law did you use to calculate this probability?

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