Blog Archives

Comparison Among Groups with Francis Parameterization

November 21, 2013
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Comparison Among Groups with Francis Parameterization

In my last post, I suggested that the Francis parameterization of the von Bertalanffy growth model may be used in cases where the typical parameterization did not converge (likely due to issues related to highly correlated parameters and data with … Continue reading →

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A Problem Fitting the von Bertalanffy Growth Model with nls()

November 19, 2013
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A Problem Fitting the von Bertalanffy Growth Model with nls()

Recently, a fishR user asked me the following (modified) question: I have successfully fit the typical von Bertalanffy growth model to all of my fish. However, when I subset the data by sex and attempt to fit the model separately … Continue reading →

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Merge Relational Dataframes

November 11, 2013
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Merge Relational Dataframes

A Question Recently, a student, working on her Senior Thesis at Northland College, asked me the following question: Attached is an Excel file with three “important to R” worksheets. The only thing that connects all 3 worksheets is the Lift.ID … Continue reading →

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Multiple Removal Estimates at Once

October 30, 2013
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Multiple Removal Estimates at Once

A Question Recently, a fishR user asked me the following question: I have recently used the FSA package to calculate Zippin depletion population estimates resulting from 3 pass removals on smaller trout streams. I have currently been doing this the … Continue reading →

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R-Squared for a VBGM

August 9, 2013
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R-Squared for a VBGM

Recently, a fishR user asked me the following question: After fitting the age-length data into VBGM, I overviewed the results. But I can’t find the coefficient of determination () for the VBGM fitting. Because some reviewer want the the coefficient … Continue reading →

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Creating Catch Data from Individual Length Measurements II

July 26, 2013
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Creating Catch Data from Individual Length Measurements II

Note that this is largely a repeat of a previous post (except that I have added a few plots at the bottom) as I am experimenting with being able to write posts here directly from R using the knit2wp() function … Continue reading →

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Creating Catch Data from Individual Length Measurements

June 6, 2013
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Creating Catch Data from Individual Length Measurements

This example has been updated in this post. I came across a “problem” today where I needed to create catch data for individual nets from length measurements made on individual fish in those nets.  In other words, I had data … Continue reading →

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Mixed Model Example — Wagner et al. (2006)

May 6, 2013
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Mixed Model Example — Wagner et al. (2006)

I am preparing for a workshop on mixed models and looked at the paper “Accounting for multilevel data structures in fisheries data using mixed models” by Wagner et al. (2006) (PDF available here).  Wagner et al. (2006) used two examples, with the … Continue reading →

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