An article in Knee Surgery, Sports Traumatology,Arthroscopy (2005, Vol. 13, pp.

Question

An article in Knee Surgery, Sports Traumatology,Arthroscopy (2005, Vol. 13, pp. 273-279), consideredarthroscopic meniscal repair with an absorbable screw. Resultsshowed that for tears greater than 25 millimeters, 14 of 19 (74%)repairs were successful while for shorter tears, 22 of 31 (71%)repairs were successful.

(a) Is there evidence that the success rate is greater forlonger tears? Use = 0.05

What is the P -value?

(a) There ( is or is not ) evidence that the success rate isgreater for longer tears. The P -value is ? Round your answer to four decimal places (e.g.98.7654).

Explanation / Answer

Given n1=19, p1=0.74            n2=31, p2=0.71 =0.05, Z(0.05)=1.645 (check normal table) (a) The test hypothesis is Ho:p1-p20 The test statistic is Z=(p1-p2)/[p1*(1-p1)/n1]+[p2*(1-p2)/n2] =(0.74-0.71)/sqrt(0.74*(1-0.74)/19 + 0.71*(1-0.71)/31) =0.23 Since Z=0.230.23)=0.409 (check normal table) (b)The 95% CI is (p1-p2) - Z* [p1*(1-p1)/n1]+[p2*(1-p2)/n2] --> (0.74-0.71)-1.645*sqrt(0.74*(1-0.74)/19 +0.71*(1-0.71)/31) --> -(p1-p2)>-0.183

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