Glossary

Enrollment terms, defined the way an invoice uses them

Most of these terms have a technical meaning and a commercial meaning. The gap between the two is where recruitment budgets disappear.

Cost per lead (CPL): What you pay for one person who submits interest. It says nothing about whether that person is eligible, reachable, or near a site. A vendor optimising CPL can make your numbers look better while your randomizations stay flat.
Cost per randomized patient: Total recruitment spend divided by patients actually randomized. The only recruitment figure that maps to your timeline. It is usually 20 to 100 times CPL, and the multiple is the real story.
Predictive Enrollment Engineering: A modeling approach, developed and trademark-pending by CT Scan, Inc. and Alen Lalic, that predicts cost per enrollment by multiplying funnel-stage probabilities against live advertising data. It does not pull from stale databases, EHR records, or patient lists.
Screen-fail rate: The share of screened candidates who do not meet eligibility. A high rate is a pre-screening or protocol problem, not a traffic problem — spending more on advertising scales the failure.
Recruitment vs. enrollment: Recruitment is generating and qualifying interest. Enrollment is consent and randomization at a site. Vendors are usually paid for the first and judged on the second.
Referral-to-randomization ratio: How many referrals a site consumes to produce one randomized patient. Compared across sites, it separates sites that can't convert from campaigns that send the wrong people.
Pre-screening: Qualification before a site visit — questionnaire, call, or chart review. Where most funnel loss happens and where it is least often measured.
Randomization rate: Randomized patients per site per month. The unit that determines whether your last-patient-in date is real.
Site activation timeline: Contract execution to site initiation visit to first patient in. Activation delays are frequently misdiagnosed as recruitment failure.