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Combine males and females at or below this bin number

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Teresa Amar, modified 5 Years ago.

Combine males and females at or below this bin number

Youngling Posts: 17 Join Date: 1/16/14 Recent Posts

Steve Barbeaux had a question about the meaning of the option in the data file to "combine males and females at or below this bin number" for length composition data.

The SS 3.24s user manual says:  "if [combine-these-bins] is greater than 0, then add males into females for bins 1 thru this number, zero out the males, set male data to start at the first bin above this bin. Note that [combine-these-bins] is entered as a bin index, not as the size associated with that bin. Comparable option is available for age composition data."

In the SS 3.24u code, males in length bins 1 through the combine-these-bins bin are added to the females, and the males are set to 0. The likelihood components for the length composition data are adjusted to include fitting to the data for length bins (combine-these-bins + 1) to the maximum bin number only.

A comparable option is available for age composition data.

 

 

Richard Methot, modified 8 Years ago.

RE: Combine males and females at or below this bin number

Youngling Posts: 222 Join Date: 11/24/14 Recent Posts

Steve,

I am unclear as to your question, so let me provide a rationale for this feature.

It is common to find that immature fish are hard to determine the sex of.  I sometimes see raw length composition data in which the smaller fish are assigned very skewed sex ratios.  If the entire length distribution is treated as a joint sex-length distribution, or if each sex is analyzed individually, the data will be aliased by this issue.

The feature in SS allows the smaller length binds to be analyzed as if they were combined gender and the larger length bins analyzed with joint sex-length distribution expectations.  Essentially this is done through an extension of the tail compression logic such that the smaller bins are compressed in terms of sex, but not necessarily in terms of length.

Rick