## MS Mod 15 Logistic regression odds ratio practice exam questions

 Author Message NEAS Supreme Being Group: Administrators Posts: 4.2K, Visits: 1.2K MS Module 15 Logistic regression odds ratio practice exam questions(The attached PDF file has better formatting.) A probability Y is related to the independent variable X by logistic regression:     Y = probability(x) = exp(β0 + β1 x) / (1 + exp(β0 + β1 x) )●    When X = 5.4, the probability Y is 31%●    When X = 6.2, the probability Y is 39%Question 15.1: Odds ratioAt X = 5.4, what is the odds ratio of Y?Answer 15.1: 31% / (1 – 31%) = 0.449(odds ratio = probability / (1 – probability) Question 15.2: Odds ratioAt X = 6.2, what is the odds ratio of Y?Answer 15.2: 39% / (1 – 39%) = 0.639(odds ratio = probability / (1 – probability) Question 15.3: Multiplicative change in the odds ratioWhat is the multiplicative change in the odds ratio, or exp(β1), when x increases by 1 unit?Answer 15.3: (0.639 / 0.449)(1/(6.2 – 5.4) ) = 1.554(the multiplicative change in the odds ratio, or exp(β1), when x increases by 1 unit, = (odds at point X2 / odds at point X1)(1 / (value of X2 – value of X1) ) Question 15.4: Odds ratioAt X = 6.9, what is the odds ratio of Y?Answer 15.4: 0.639 × 1.554(6.9 – 6.2) = 0.870(odds ratio at point X3 = odds ratio at point X2 × (multiplicative change in odds ratio)(value of point X3 – value of point X2) Question 15.5: Probability of YAt X = 6.9, what is the probability of Y?Answer 15.5: 0.870 / (1 + 0.870) = 46.52%(probability = odds ratio / (1 + odds ratio) Attachments MS Module 15 Logistic regression odds ratio practice exam questions.pdf (231 views, 32.00 KB)
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