545: Synchronous Predictors

By default, CPT assumes that the predictors should proceed the predictands, and will select starting dates for the X and Y files so that the Y data begin at the first possible date after the starting date for the X file. However, when exploring sources of predictability, there may be interest to explore synchronous relationships between the predictors and predictands. For example, there may be interest in exploring how June - September (JJAS) sea-surface temperatures (SSTs)are related to June - September rainfall; only if there is a relationship does it seem reasonable to then try predicting July - September rainfall using May temperatures. However, if you open files of JJAS SSTs and JJAS rainfall, CPT will set the start for the Y file as one year later than for the X file, and possibly reduce the length of the training period by one. To prevent CPT from assuming this lag, switch on the Synchronous Predictors option.

If the Y file contains monthly data, and the Synchronous Predictors option is switched on, CPT will automatically set the target season to be the same as the predictors. For example, if you open files of JJAS SSTs and monthly rainfall, CPT will set the target season for the Y file as JJAS and will set the starting dates for the X and Y files to be the same. It is still possible to reset the target season using the Edit ~ Target Season menu item. For example, if you open files of JJAS SSTs and monthly rainfall, but want to consider the July - October rainfall season then reset the target season using Edit ~ Target Season after opening both files.

If the Synchronous Predictors option is switched off, CPT will prompt for the target season if the Y file contains monthly data since CPT assumes that you are trying to create a forecasting model, but it does not know which season you want to predict. So the Synchronous Predictors option suppresses the target season prompt if the Y file contains monthly data. If the Y file does not contain monthly data, but the Synchronous Predictors option is on, CPT will assume the shortest possible lag, and will not prompt for the season.

Selecting the Synchronous Predictors menu item will toggle the option on and off. A tick mark is shown by the menu item if the option is on.