What Each Recruitment Channel Really Costs You Per Enrollment

Most sites can tell you what they spent on recruitment last quarter. Far fewer can tell you what a single randomized participant cost them by channel. That gap is why budgets keep going to the loudest channel instead of the most productive one.

Start with a denominator you can defend

Cost per enrollment only means something if everyone agrees on what "enrollment" is. Pick one:

• Cost per consented participant — useful when the sponsor pays per consent or when screening labs are reimbursed.
• Cost per randomized participant — the number that matters for most contracts and the one sponsors recognize.

Track both if you can, but report randomization as the headline. Cost per consent flatters channels that send you people who look eligible on paper and wash out at labs.

Count every dollar, not just the ad spend

The most common error is comparing paid media invoices against channels that look free. A database recall campaign has no ad cost, so it appears infinitely efficient — until you price the coordinator hours spent calling 300 records.

Build a cost model with three buckets:

1. Direct spend — ad platform charges, printing, radio buys, vendor referral fees, community event sponsorships.
2. Staff time — hours spent on outreach, pre-screening calls, and no-show rework, multiplied by a loaded hourly rate. Use a blended rate per role and keep it consistent across channels.
3. Clinical cost absorbed — screening visits you perform that will not be reimbursed if the participant screen-fails. This is where channels with weak filtering quietly get expensive.

Staff time is almost always the largest line for referral partners and database recalls, and it is almost always the one left out.

Attribute at intake, not in retrospect

Deciding where a lead came from after they enroll is guesswork. Capture source as a required field at first contact, with a short closed list — paid social, search, database recall, physician referral, patient referral, community event, registry vendor, walk-in. Resist free text. Resist "other" as a habit.

For participants who touched multiple channels, pick a rule and write it down. First-touch attribution is simplest and usually good enough for budget decisions. What matters is that the same rule applies every month.

Read the number in context

A high cost per enrollment is not automatically bad. Evaluate each channel on three dimensions:

• Cost — dollars per randomized participant.
• Volume ceiling — can it produce ten more participants, or is it tapped out? Physician referrals often have excellent economics and almost no scalability.
• Speed — how many days from first contact to randomization. For a study with a hard enrollment deadline, a faster expensive channel can beat a cheap slow one.

Sites commonly find that paid media looks worst on cost and best on volume and speed, while referrals and database recalls look best on cost and worst on scale. The right answer is usually a mix, not a winner.

Make it a monthly habit

One spreadsheet, updated monthly, with rows for channels and columns for spend, staff hours, consents, randomizations, and days-to-randomize. Review it in the same meeting where you discuss enrollment against target.

After two or three studies you will have a credible per-channel benchmark by therapeutic area — which is exactly what you need to build a realistic recruitment budget during startup instead of guessing and absorbing the overage.