In some cases you might want to prevent the randomization of certain participants. This can be participants that are not eligible for randomization or for studies where only a subset of the patients is being randomized.

While it is not possible to hide the randomization tab for certain participants, you can make use of the fact that all strata fields have to be filled in in order to randomize a participant.

Option 1

Set exclusion validation messages on your conditions for randomization, such as the inclusion criteria. If an exclusion message is set on the fields that contain inclusion criteria and the inclusion criteria are not met, the exclusion message will be activated and prevent any further actions in the study - including randomization. 

Option 2

1. Check your conditions for randomization by using a calculation field. This can be, for example, a calculation field that determines if all inclusion criteria are met. In this case, you can use the following calculation template:

if ({variable_1} == 0 && {variable_2} == 0 && {variable_3} == 1) {
 1;
} else {
 0;
}

1.  Create a radiobutton field that is dependent on the calculation field being equal to 1. The label of this field can be for example: "Can this patient be randomized?". This field needs only one option: "Yes". Since it is a dependent field, it will appear only when the calculation is equal to 1, i.e. only when my conditions are met.
2. Add this radiobutton field as a stratum in the randomization settings, and that will block the randomization until it has been answered. Since there is only 1 option in this field, there are no consequences to the randomization or the statistical outcome.

Option 3 - if you are stratifying per site

1. Create a radiobutton field with a selection of all sites that are participating in the randomization. 
2. Make this field dependent on a calculation similar to Option 1 or another field that might be indicative of the randomization conditions being met. This means that the field will appear only when the conditions are met.
3. Add this radiobutton field as a stratum in the randomization settings. Select 'No' for stratifying on site in the left panel of the randomization settings, since the stratification will be done on the field you have added.
4. You can also add a calculation to check if the selected site corresponds to the site abbreviation of the participant. For this you can use "{castorInstituteAbbreviation}" in a calculation field.

Please note: Strata fields cannot be modified after going live, so if you need to add an site to this selection, we will have to do that for you.