[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

From |
"Nick Cox" <[email protected]> |

To |
<[email protected]> |

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

Date |
Mon, 25 Jul 2005 21:19:43 +0100 |

Your objection that expected frequencies don't come out as integers is discussed in any good textbook. Briefly, it is just the way the calculations come out: it is not a cause for concern. In my opinion by far the best way to check for normality is to use -qnorm-. Nick [email protected] Siddharth Kharkar > 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.. * * 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/

- Prev by Date:
**st: RE: Extracting a variable of a varliable list** - Next by Date:
**st: RE: Multi-stage OLS loop** - Previous by thread:
**st: RE: Extracting a variable of a varliable list** - Next by thread:
**st: percentiles and locating a scalar in there.** - Index(es):

© Copyright 1996–2024 StataCorp LLC | Terms of use | Privacy | Contact us | What's new | Site index |