When performing a trend analysis within a category to estimate missing data with the Toolbox, the default X-axis descriptor is log Kow, which is estimated with the EPISUITE program (1) [see screenshot below]. While this descriptor may be pertinent for many endpoints, e.g. aquatic toxicity, alternative descriptors may be warranted for other endpoints (e.g. vapour pressure for acute inhalation toxicity).

There are two types of descriptors in the Toolbox – active descriptors (or Descriptors in use (1)) and inactive (or Available descriptor (2)). Both types of descriptors are listed separately in the in the tab Descriptors (3) [see screenshot below]. Active descriptors are the descriptors that were used in the calculations for predicting the endpoint. Inactive descriptors are all the other descriptors supported by the Toolbox but which were not used for predicting the endpoint.

In the Prediction tab (1) the distribution of the observed data for the endpoint is plotted against any descriptor. By default, the Toolbox selects the first active descriptor to plot the available data. In case of trend analysis the equation line of the model is also visible. 

If the user changes the descriptor, he/she will see how the observed data for the endpoint is distributed against the newly selected descriptor.

It is possible to change the descriptor and re-estimate the property. For that the user has to click the box of Descriptor X under the trend analysis graph (2). A list of available descriptors appears. The user can select a new descriptor from the list.

By clicking on the new descriptor (in this example “Molecular weight”), the selected descriptor is shown in the Descriptor X box (3) and the new descriptor appears also in the trend analysis graph.

At this stage, however, the equation is NOT yet re-estimated. To make a prediction using the newly selected descriptor the user must activate it. This is done by clicking Descriptors/data (4) on the right-hand menu and then selecting Make active descriptor (5) [or by dragging the new descriptor from the Available descriptors list to the Descriptors in use list in the Descriptors tab].

A dialogue box asking for confirmation of replacing the descriptor pops up.

By clicking the Yes button, the trend analysis for the new X-axis descriptor is completed.