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Number of observations for logistic regression

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New Contributor
Posts: 3

Number of observations for logistic regression

Hello,

I'm new SAS user; I performed a logistic regression of 68 observations, but this is not significant. A friend advised me to take two or three times the number of observations that I have is to say the same thing but in two or three times. When I do this, then the regression is significant. But have I the right to do so?
If not, what can I do? I think this is my échatillon of studies was small.

Respected Advisor
Posts: 4,751

Re: Number of observations for logistic regression

Don't do that. One of the key assumptions for inference in logistic regression is the independence of observations. Duplicated obs are definitely not independent.

 

What you can do:

 

  • Plot the data. Make sure there are no outliers.
  • Consider using another statistical model.
  • Get more independent data.

Good luck.

PG
Super User
Posts: 10,871

Re: Number of observations for logistic regression

How many independent variables are you using? How many levels are there for each of those? Too many varaibles/levels will often leave nothing signficant as there are not enough observations in any group.

 

Also, models are NOT required to have a signficant difference. The fact that there isn't may well mean that there is not sufficient influence on the population from your variables.

Super User
Posts: 18,569

Re: Number of observations for logistic regression

This implies that your study was under powered, you didn't have enough samples to find a significant difference - based on the observed difference. 

 

 

Super User
Posts: 9,775

Re: Number of observations for logistic regression

[ Edited ]

You have small sample data. Try EXACT logistic regression.

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