So many choices! Prism's nonlinear regression dialog has ten tabs (eleven when performed from the multiple variables data table), and can seem overwhelming at first. But you don't have to learn about all the choices when you first fit a curve.
If your goal is to fit a standard curve from which to interpolate unknown values
If your goal is to interpolate from a standard curve, you can ignore most of the choices that Prism offers. You do need to pick a model, but you should judge the adequacy of the model visually. If it goes through the points without wiggling too much, it is fine for interpolation. Note that Prism offers a simplified curve fitting analysis for interpolation.
If your goal is to fit a model to determine best-fit parameters
If your goal is to fit a model to determine parameter values, then choosing a model is the essential first step. You should not expect a computer (or a software company's tech support) to choose a model for you. Choosing a model, and deciding which parameters should be constrained and which should be shared among data sets, is a scientific decision that is fundamental to analyzing your data. The other choices are useful, but can be put aside when you are first learning curve fitting.
If you're performing nonlinear regression from a Multiple Variables data table
When performing a nonlinear regression analysis from an XY data table, it's obvious which column contains your X values (the X column) and how your Y values are assigned to different groups (each group has its own individual Y column). However, when performing nonlinear regression from the Multiple Variables data table, you must let Prism know which variable contains your response (Y) values, which variable contains your predictor (X) values, and how your response values should be grouped (using optional grouping variables). These assignments are made on the Data Tab of the parameters dialog, and make it easy to perform this analysis from data structured in this very standard way without requiring you to re-arrange or re-structure your data to get it into an XY data table.
