Difference between revisions of "Sandbox"
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<td> <div align="center">12</div></td>  <td> <div align="center">12</div></td>  
−  +  The results are:  
+  Difference = p (1)  p (2)  
+  Estimate for difference: 0.170035  
+  95% CI for difference: (0.0346494, 0.305420)  
+  Test for difference = 0 (vs not = 0): Z = 2.37 PValue = 0.018  
+  Fisher's exact test: PValue = 0.026  
+  Discussion  
+  1. Why is the Fisher exact test PValue (0.026) to be preferred to the other PValue mentioned (0.018)?  
+  2. The Wall Street Journal mentioned several caveats “making it difficult to determine the underlying reasons for the afterhours patients’ poor outcomes.” List a few practical significance hedges to the statistically significant result.  
−  +  <td> <div align="center">70</div></td>  
−  +  <td> <div align="center">.1714</div></td>  
−  +  </tr>  
−  +  </table>  
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Revision as of 14:04, 13 September 2009
Breaking News
The Wall Street Journal of September 8, 2009 reports on a study in the Journal of Bone and Joint Surgery: “The researchers compared the outcomes of patients who underwent surgery between 6 a.m. and 4 p.m. for fractures of the femur or tibia to those who had comparable surgeries for similar fractures outside those normal hours.”
The results are:
Difference = p (1)  p (2) Estimate for difference: 0.170035 95% CI for difference: (0.0346494, 0.305420) Test for difference = 0 (vs not = 0): Z = 2.37 PValue = 0.018
Fisher's exact test: PValue = 0.026
Discussion
1. Why is the Fisher exact test PValue (0.026) to be preferred to the other PValue mentioned (0.018)?
2. The Wall Street Journal mentioned several caveats “making it difficult to determine the underlying reasons for the afterhours patients’ poor outcomes.” List a few practical significance hedges to the statistically significant result.
Sample  Reoperations Needed 
Sample Size 
Sample Proportion 

Outside Normal Hours  28 
82 
..  
Within Normal Hours  12 
70 
.1714 