Let's dissect the components of a rule. A rule basically looks like this:
IF {condition A} THEN {Do B} ELSE {Do C}
the ELSE clause is optional and it is assumed to default to "do nothing" if condition A is not met.
Rules can be complex :
IF {condition A} THEN {
(IF {condition E} THEN {Do F} ELSE {Do G} }
ELSE {Do C}
Evaluating a Rule is an Activity whose outcome is binary: either the condition(s) is/are met ("true") or not met ("false"). One could argue for a 3rd category, not applicable, for cases where the reason to have a rule in the first place doesn't apply (e.g. when to conduct a pregnancy test in a male)
In clinical studies, rules often depend on other activities. I call these prerequisite activities (PA). For example:
IF {migraine occurs} THEN {take study drug}
or a more precise way of expressing it:
IF {headache assessment = MIGRAINE} THEN {take study drug}
In this case the prerequisite activity is a headache assessment and the condition is met when the headache assessment outcome indicates that a migraine is present.
Regarding how prerequisite activities are evaluated, sometimes it is sufficient that the PA simply has begun (PA status = started) or completed (PA status = complete) or, more commonly, completed with a specific expected outcome (PA expected outcome = migraine).
When looking at rules more closely, they can be expressed as start rules for other activities. Let's call these target activities (TA).
Target Activity: Study Drug Administration_01
Start Rule: MigrainePresent_01 -- Prerequisite Activity: HeadacheAssessment_01
PA Expected ActivityOutcome: MIGRAINE
StudyDrugAdministration_01 is a planned activity that just sits there, waiting to be performed. As soon as the headache assessment is performed and whose outcome is a documented MIGRAINE, the rule outcome is set to TRUE and the target activity can begin.
One can add qualifiers in the rule to describe exactly when the target activity is performed. for example a delay = 30 minutes means wait exactly thirty minutes after the condition is met before starting the activity. maxdelay = 60 minutes means wait no more than 60 minutes before starting the activity. mindelay = 30 minutes means wait a minimum of 30 minutes before starting the activity.
I have tried this paradigm in multiple scenarios and so far it seems to work (randomization, eligibility determination, delayed start, assessments).
In a future post, I'd like to explore how these rules can be expressed computationally using the RDF.
