Programming the statistical procedures from SAS

Trends over time

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Occasional Contributor EMB
Occasional Contributor
Posts: 5

Trends over time

Hello,

I wish to study trends in age over time in 3 large samples (>1000 individuals each) from the same population and get p for linear trend.

Samples are independent and data are available for 4 time periods separated by equal time-intervals.

Would the following be correct? Any other suggestion?

 

proc glm;
class (time period);
model AGE=(time period);
contrast 'linear' (time period) -3 -1 1 3;
run;

 

Thanks!

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Posts: 1,615

Re: Trends over time


EMB wrote:

Hello,

I wish to study trends in age over time in 3 large samples (>1000 individuals each) from the same population and get p for linear trend.

Samples are independent and data are available for 4 time periods separated by equal time-intervals.

Would the following be correct? Any other suggestion?

 

proc glm;
class (time period);
model AGE=(time period);
contrast 'linear' (time period) -3 -1 1 3;
run;



There are a few things you haven't told us, such as:

 

  1. For each individual, are the time intervals exactly the same?
  2. How can age be a response variable? If you measure the idividual's age at four different time periods ... isn't the individual's age already a known function of the age at the first time interval, plus the delta between the other intervals? What is the source of randomness in this data?
Occasional Contributor EMB
Occasional Contributor
Posts: 5

Re: Trends over time

The study includes incident cases of a specific disease, and data are collected at defined periods, each period includes different participants.  As part of the descriptive analysis I would like to look at trends over time in age of the diagnosed individuals.

Trusted Advisor
Posts: 1,615

Re: Trends over time

[ Edited ]

EMB wrote:

As part of the descriptive analysis I would like to look at trends over time in age of the diagnosed individuals.


I am totally not understanding this part.

 

Trends of what? Your sentence (and code) implies you want to find the trend over time of AGE. That cannot be right. Your age increases 1 year for every 1 year  of change in time. No statistics or regression or p-values needed.

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