Your Enrollment Problem Isn't a Site-Selection Problem. Here’s Why.

You selected your sites carefully. Six months in, enrollment is behind. The instinct: find better sites, bring more online.

But site selection wasn’t the constraint. Narrow eligibility criteria were eliminating patients before a site could enroll them.

In a Parkinson's Market Feasibility Test (a patient survey run before a single site opens) only 4% of 214 respondents qualified despite strong awareness. Every person who qualified wanted to participate. One narrow eligibility requirement created the bottleneck, not a site-selection decision. And the test found it before a single site opened.

Your enrollment plan assumes too much

This skew is structural, not anecdotal. A small share of sites drives most enrollment. Yet most recruitment plans still assume balanced contribution, setting your timeline, budget, and board expectations on a foundation that rarely holds. 

37% of sites under-enroll.

11% never enroll a single patient.

 Source: Antidote Parkinson's Market Feasibility Test, 214 respondents (2025) 

Why adding sites makes the problem more expensive

When enrollment slips, the reflex is to add sites. It's a rational move: more sites should mean more patients, and it's the fastest lever available. But that reflex carries costs most plans underprice:

• Adding sites takes months and burns budget before a single patient enrolls.
• Newly added sites are statistically the most likely to underperform.
• Volume does not fix a shortfall rooted in market fit. It compounds the cost.

The real question isn't how many sites to add. It's whether the patients your protocol requires exist in the markets you're considering, and you can answer that before you open a single site.

A Market Feasibility Test identifies qualification bottlenecks, narrows eligibility criteria, and patient-facing friction before a site is selected. Sponsors test whether eligibility requirements hold against real patient populations before building a site network around a protocol that can't deliver.

Test the market before you commit.

Before you commit to a site network:

• Define the eligibility criteria most likely to eliminate patients.
  • Antidote tests the requirements that carry the highest risk, before they cost you a site.

• Survey real patients against those criteria.
  • Not registries, but actual patient response.

• See the qualification rate before you build around it.
  • If patients can't meet the eligibility criteria, you know in weeks, not after six months of underperforming sites.
    
    

In Antidote’s Parkinson’s MFT, this caught it early: only 4% of respondents met the device-history requirement, despite strong awareness. The signal surfaced before any site went live. Thus, the team narrowed the eligibility window instead of expanding the network.

Site coverage was never the constraint. Eligibility criteria were.