st: GLM - offset needed?

[Jennifer Devine <jdevine@mun.ca>]

I'm running a GLM  on fish catches that were collected with different gears 
over time.   It was suggested to me that if area swept differed between the 
gears, I would need to adjust for that by using an offset with the offset = 
area swept by the gear.  However, I'm running into problems on how to set 
this up. I've made a new variable in my data called offset and for each 
gear type, I have replace offset=area swept for that gear. Area swept is in 
sq. nautical miles and is less than one.  My model is: glm catch yr strat, 
f(nb) link(log) off(offset).  This is where I run into problems - is my 
offset correct? My data, visual inspection, linear regression, GLM, all 
show a decline over time without the offset. Once the offset is added, my 
results are a mess. Can someone please help?

Thank you,
Jennifer

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