EXPLORING MODELS IN EXCEL
|
![[Link Map]](../../icons/smartnav.gif)
|
Formulas can be used in Excel to plot graphs of the generalised logistic and
Gompertz curves, enabling the user to explore various values for the parameters.
-
Step 1
-
Input the constant values for A, C, T and M in cells on a spreadsheet as shown below.
-
Step 2
-
Input the values for time (x) down the first column, e.g. 0, 10, 20 ...
-
Step 3
-
Using the formula toolbar, type in the formula for the generalised
logistic growth curve for the first y cell, typing in the numeric values of the constants
not the cell referencing them.
e.g. = A2 + (B2 / POWER((1 + (C2 * EXP(-D2 * (A5 - E2)))), 1 / C2)))
-
Step 4
-
Highlight the cell, with the formula and drag the bottom right corner down
to the row of the last x values. Use 'replace' to replace the numeric values
of the constants with their cell references.
-
Step 5
-
Highlight the cells containing the values (x and y), and
use the chart wizard to plot them. Now any of the x values and constant
values can be changed and the results examined.
A screen shot from an example run is shown below.
Growth curve modelling 1.6.95 Page : 12d of 12
|
|