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There are 250,000 people attend the fair, 1% visit the pavilion for screening services equals

(0.01×250000)=2500 people, prevalence for hearing loss is 0.18×2500=450, 90% Sensitivity and 96% specificity, contingency table listed below:



Screening Test                        Present                                   Absent                        Total= (a +b) =487                                        Positive (a +b)            Hearing Lost             Hearing Lost

(a)   405

(b)  82

(c)   45

(d)  1,968

                                               (c+d) = 2013

Negative (c+z)   Total: (a+c) = 450 (b+d) =2050 = 2,500

Calculation: 0.90a÷450, a= 0.90 ×450 or a=450, 0.96=d÷2, 050, d=0.96×2,050or d=1, 968, 0.91b=2,050-1,968=82, c=450-405=45

  1. Construct a 2-by-2 contingency table to determine the total number of people who fail the diagnostic test, which represents the target market for hearing aid sales.
  3. A total of 487 people tested positive for hearing loss and will be referred for follow-up diagnostic testing.



Screening testing                           Present            Absent                                                                                                            (hearing lost)              (hearing lost)                                                                                                                                                                                                                                                








(a + b) =402


(c + d)=85






Total                        (a+c) =405               (b+d) =82        (a+b+c+d) =487


0.99=a÷405, a=0.99×405or a=401, 0.99=d÷82, d=0.99×82or d=81, b=82-81=1, c =405-401=4

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