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From |
"Siddharth Kharkar" <[email protected]> |

To |
<[email protected]> |

Subject |
st: Two problems: Pre-post intervention AND comparing z-score distribution in a specific poopulation v/s the normal distribution. |

Date |
Mon, 25 Jul 2005 09:09:18 -0400 |

Hi, I am most grateful for all the knowledge you people dispense on statalist. I have learnt a lot through it. I have two problems: 1) The first one concerns the effect of two different interventions: At baseline, 20 % of patients admitted with disease X at Hospital 1 were cured At baseline, 30 % of patients admitted with disease X at Hospital 2 were cured Training 1 was given to doctors in Hospital 1 Training 2 was given to doctors in Hospital 2 In the Post-intervention period: 60 % of patients admitted to Hospital 1 were cured 55 % of patients admitted to Hospital 2 were cured Obviously, Training 1 seems to work better than Training 2. O How can it be shown that this "difference in improvement in cure rates" is statistically significant? i.e. one training is better than the other? (Note: This is NOT paired data.. the patients are different) s Can a sample size be calculated for this situation? I know its not a perfect study, but given the current situation, what can be done? The best I was able to do was to calculate the 95 % CI for the improvement in cure for hospital 1, then calculate the 95 % CI for improvement in cure for hospital 2. The CIs overlapped, indicating that the "improvement in cure rates" were not statistically different. 2) Comparing Z-score distribution in a study group with mental difficulties against the normal population: Scores on a cognitive test were measured in a group of students drawn from an institution for the mentally challenged. z-scores were calculated for these cognitive scores using means and SD for this test in the general population. A person had a z-score of lesser than -2 (i.e. was below 2 SD on the curve for normal individuals) was considered to be "Cognitively deficient" A person with a z-score of -2 to -1 was labeled as "Borderline Cognitive functioning" Say the scores in the study group were as follows: Normal (>-1SD) 50 % (8/16) Borderline (-1SD to -2SD) 25 % (4/16) Deficient (below -2 SD) 25 % (4/16) These values are obviously abnormal. The values expected based on the z-score distribution for normal people are: 84 %, 13.5 % and 2.5 % respectively. What is the best way to show that the distribution of Z-scores in the mentally challenged children was abnormal? What statistical test can be performed? I was thinking in terms of making another column "NUMBER of people expected if the distribution was normal, given a sample size of 16" and then doing a chi2 on the observed v/s expected categories. The problem is that the "Number of expected people" will be a decimal number e.g. 2.5/100 x 16 = 0.4. which doesn't make much sense.. A big THANK YOU for any replies that follow. I have been a keen follower of statalist and cant thank you guys enough for all that I have learnt through it. Thanks and regards, Siddharth Kharkar. * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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