```Date: Wed, 19 Apr 2006 09:53:49 -0300 Reply-To: Hector Maletta Sender: "SPSSX(r) Discussion" From: Hector Maletta Subject: Re: Minimum number of cases for computing correlation Comments: To: Rita Clivio In-Reply-To: <4tkn68\$9s6t43@ibs01.interbusiness.it> Content-Type: text/plain; charset="us-ascii" Rita, There is no simple answer to your 'simple' question. Consider the following factors: 1. Regression may involve any number of variables. An old rule of thumb, not very well justified, says you need at least ten cases per variable. That is an absolute minimum: better results need more. 2. As you suspect, finite populations may help. The standard error of an estimate (or the size of the sample needed for a given standard error) is affected by the so called finite population correction which is (N-n)/(N-1) where N=population and n=sample size. This you should look up in a statistics text for more details. 3. A regression with a given sample size may be statistically significant if all cases lie near the regression line, or not if cases are more scattered around. If your data closely conform to a linear equation you may need a smaller sample. Hope this helps. Hector -----Mensaje original----- De: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] En nombre de Rita Clivio Enviado el: Wednesday, April 19, 2006 7:25 AM Para: SPSSX-L@LISTSERV.UGA.EDU Asunto: Minimum number of cases for computing correlation Dear List I have a simple (?) statistics question. When you run a correlation, which is the minimum number of case you have to consider ? For regression maybe is 30 cases ? Under 30 cases regression is not recommended. Is always referred to my population, i.e. 7 cases from a population of 50 units and 7 cases from a population of 1000 units are different ? Thanks in advance Rita ```

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