# 15.3.8.2 Comparing Two Models (OriginPro Only)

This tool is used to compare two fit results of the same data, using two different fitting functions. This includes results from global fitting operations, where multiple datasets are fit simultaneously, with or without parameter sharing (requires OriginPro 2017).

Three tests are available for determining which model is best: F-test, Akaike Information Criterion (AIC) and the Bayesian Information Criteria (BIC) test.

To use this tool,

1. Perform fitting twice using two different fitting functions for the same fitting data, and create two fitting reports.
2. Select Analysis: Fitting: Compare Models from Origin menu.
 Example: Suppose we have a dataset and want to see which model is the best fit model for it. Candidate models are: ExpDec1: $y=y_0+Ae^{-x/t}$ ExpDec2: $y=y_0+A_1e^{-x/t_1}+A_2e^{-x/t_2}$ Steps: 1.Import Exponential Growth.dat on \Samples\Curve Fitting folder 2.Highlight Col(B), select Analysis: Fitting: Nonlinear Curve Fit to open dialog. Set Function as ExpDec1. Click OK to get result sheet 3.Open Nonlinear Curve fit dialog again, Set Function as ExpDec2 this time. Click OK to get result sheet 4.Select Analysis: Fitting: Compare Models to open dialog 5.Click browse button to open Report Tree Browser and select 1 item for Fit Result1 6.Repeat same operation to select another item for Fit Result2 7. Select all options in GUI and click OK 8.From F-test table and AIC result table, we can draw conclusion that ExpDec1 function is the best fit model

## Dialog Controls

### Recalculate

Specify the way to recalculate and update the result if there is any change in the input data.

 None The output will not be connected to the source data and any changes to the source data will not result in an update of the result. The results automatically update when source data changes. The output will not automatically update when the source data changes. You will have to manually initiate the update.

### Fit Result1

Specify the first fitting result. Click Report Tree Browser button on the right of Fit Result1 box, all fitting reports are shown in the Report Tree Browser dialog. You can choose a fitting report as Fit Result1 in the Report Tree Browser dialog.

### Fit Result2

Specify the second fitting result. Click Report Tree Browser button on the right of Fit Result2 box, only fitting reports whose fitting data are the same as Fit Result1's are shown in the Report Tree Browser dialog. You can choose a fitting report as Fit Result2 in the Report Tree Browser dialog.

Note that Origin does not support comparing a fitting result using the Levenberg/Marquardt (L-M) algorithm with a fitting result using the Orthogonal Distance Regression (ODR) algorithm. For example, if Fit Result1 is an explicit function using the L-M algorithm, fitting result of an implicit function (which uses ODR) for the same data will not be shown in Fit Result2's Report Tree Browser dialog.

### Comparison Method

Specify methods to determine which fitting function is better.

Akaike Information Criterion (AIC) Use an Akaike Information Criterion (AIC) test for comparison. Use a Bayesian Information Criteria (BIC) test for comparison. Use an F-test for comparison. Checking the box adds a Significance Level box. Default is 0.05. Values between 0 and 1 are supported.