A hard-to-change (HTC) factor is a factor that is difficult to randomize completely because of time, control or cost constraints. For example, temperature is a common HTC factor. This is because adjusting temperature often requires separate incubators, where blocks of runs are tested simultaneously across microtiter plates in incubators set at different temperatures.

Specifying that a factor is HTC will ensure your design adds replication into your different HTC blocks, such that the effect of the HTC factor can be discerned from the effect of splitting your runs into different plates.

In Synthace, this specifically relates to any factor specified in the Mixture Composition, Diluent To Use or Final Target Volume parameters in both the Make Mixtures and Mix Onto elements or to custom factors.

In this tutorial you will learn:

How to set a categorical factor as HTC.

Defining a HTC factor

Build a workflow that defines a set of liquids and provides those liquids to a Make Mixtures element.
Switch the workflow builder into DOE Mode.

Note: only the elements that can have DOE factors applied to their parameters will be interactive and display in colour.
Select the ‘Design’ button, in the top right-hand corner, to open the DOE design window.

Note: factors within Diluent To Use and Final Target Volume can also be specified as HTC.
Click on the “ADD” button to select a factor type.
Select the “New Factor” Option to open the Factor Definition Panel.
In the Factor Definition Panel, select Numerical as the factor Kind, enter the Factor Name, Unit and Levels of the factor that will be HTC. In this example, Temperature has been added as a Custom Factor.
Click on the Hard to Change button.
Click on “Add Factor” to save the factor to your Factor Table where you will see a summary of the factors settings.