Understanding changes in LOG OUTPUT in small samples

deengyn — Fri, 14 Jan 2022 19:46:08 GMT

Hi all,

I'm doing a school project on complications occurring within 30-days post-op, it was defined as a binary variable.

The sample is small (n = 139) and we have decided on 5 variables:

Age (continuous)
Comorbidities (binary)
Diagnosis type (3 class category)
Treatment type (3 class category)
Sex (binary)

Now, I've done collinearity, univariate logistic analyses, and then eventually onto the multivariate logistic. It was stable, everything looked great.

My supervisor suggested looking at 2 additional numeric variables which were also part of our dataset; in clinical terms, it would pose a great question and it has to do with treatment.

So I did some exploratory work. I looked into the variables, performed the same steps of looking into scatter plots, univariate, etc etc.

I tried the full model with 7 variables and again, stable. The output wasn't far from the initial with 5.

However, should I change the code and add

units age = 5;

SAS would not output it. I'm sure it has to do with sample size, but could someone help me understand the background of this.

Re: Understanding changes in LOG OUTPUT in small samples

Reeza — Fri, 14 Jan 2022 19:56:58 GMT

@deengyn wrote:

However, should I change the code and add
units age = 5;
SAS would not output it. I'm sure it has to do with sample size, but could someone help me understand the background of this.

What did the log or error message show? Please post the log/error.

AFAIK UNITS would only affect the calculation of the odds ratio, everything else should remain the same.

@deengyn wrote:

Hi all,

I'm doing a school project on complications occurring within 30-days post-op, it was defined as a binary variable.

The sample is small (n = 139) and we have decided on 5 variables:

Age (continuous)

Comorbidities (binary)

Diagnosis type (3 class category)

Treatment type (3 class category)

Sex (binary)

Now, I've done collinearity, univariate logistic analyses, and then eventually onto the multivariate logistic. It was stable, everything looked great.

My supervisor suggested looking at 2 additional numeric variables which were also part of our dataset; in clinical terms, it would pose a great question and it has to do with treatment.

So I did some exploratory work. I looked into the variables, performed the same steps of looking into scatter plots, univariate, etc etc.

I tried the full model with 7 variables and again, stable. The output wasn't far from the initial with 5.

However, should I change the code and add
units age = 5;
SAS would not output it. I'm sure it has to do with sample size, but could someone help me understand the background of this.

topic Understanding changes in LOG OUTPUT in small samples in Statistical Procedures

Understanding changes in LOG OUTPUT in small samples

Re: Understanding changes in LOG OUTPUT in small samples