PiscesLogoSmallerStill W Ford-Walford Tab

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This tab presents the Ford-Walford plot of your weight data. It shows a plot of weight at t+1 against weight at t which was used as a graphical method to solve the von Bertalanffy growth equation. It is only shown if you run a von Bertalanffy growth model. This plot can be useful to help you estimate initial parameters for nonlinear regression. Marked on the plot is the 45 degree line and the best fit through the observed points as found by least squares. The point where these two lines intersect is an estimate of W (asymptotic weight).

 

The graph below shows a typical example using the bass.csv data. The red line marks the estimate of W, which is about 4,500 g (4.5 kg) for these data (the non-linear regression method estimated a value of 4.415 kg showing that the graphical method can give similar results). However, this plot does indicate that this estimate should be viewed with caution as it is an extreme extrapolation. This method was the standard method to estimate L in fisheries science until the 1980s.

 

 

weight Ford walford plot