Adding Sites Is Expensive.

More Sites Solve One Specific Problem

More sites are valuable when the study genuinely has:

• insufficient patient access,
• insufficient geographic reach,
• insufficient site throughput,
• or insufficient investigator capacity.

But slow enrollment can also happen when the study already has enough potential participants.

The problem may instead be:

• sites are receiving low-quality candidates,
• coordinators are screening too many unlikely patients,
• eligible patients are waiting too long for follow-up,
• external medical evidence is missing,
• consent takes too long,
• participants face logistical burden,
• or payment/reimbursement creates friction.

In those situations:

more sites increase volume without fixing conversion.

5. The Core Decision

Ask one question: If candidate volume doubled tomorrow, would randomized enrollment approximately double too?

If yes:

You may genuinely have a capacity or reach problem.

If no:

Something downstream is limiting throughput.

That distinction should come before site expansion.

6. Diagnostic Part 1 — Is Patient Supply the Constraint?

Check these signals

Signal 1 — Strong conversion among current candidates

Current candidates convert well from:

identified → pre-screened → screened → randomized.

But there simply are not enough of them.

This supports a capacity/supply diagnosis.

Signal 2 — Existing sites are operating near realistic throughput

Site teams are not sitting on large backlogs.

They are following up quickly.

Their conversion rates are reasonable. They simply do not have enough eligible patient volume.

Signal 3 — Geography is genuinely limiting reach

There are qualified patients outside the current site footprint.

Travel distance is preventing participation.

New regions would materially expand access.

Signal 4 — Current patient sources are already performing efficiently

Referral partners, site databases, and recruitment sources are generating reasonable-quality candidates.

The issue is insufficient scale, not poor quality.

If all four are true

Adding sites, regions, or recruitment channels may be justified.

7. Diagnostic Part 2 — Is Conversion the Constraint?

Check these signals

Signal 1 — Candidate volume is healthy but randomization is weak

Many patients enter the funnel.

Few become randomized participants.

This suggests leakage after candidate acquisition.

Signal 2 — Screen-failure rate is high Especially if failure reasons include:

• missing evidence,
• protocol interpretation,
• timing,
• operational delay,
• consent issues,
• participant burden.

Adding sites may reproduce the same failure pattern.

Signal 3 — Site response times are slow

Qualified candidates are waiting days for:

• review,
• outreach,
• pre-screen,
• consent,
• scheduling.

This is a workflow problem.

Signal 4 — Sites vary dramatically in conversion

If some sites convert similar candidate populations far better than others, the issue may be:

• coordinator workflow,
• site process,
• training,
• prioritization,
• or operating discipline.

Opening more average-performing sites may dilute performance.

Signal 5 — Missing records delay screening

Potentially eligible patients cannot advance because:

• labs,
• diagnoses,
• medication history,
• imaging,
• or prior records

are unavailable.

That is a data-access problem.

Signal 6 — Participants decline after initial interest

Reasons may include:

• travel,
• visit burden,
• work disruption,
• childcare,
• reimbursement complexity,
• payment delays.

That is a participant-experience problem.

If several are true

Site expansion should not be the first response.

8. Diagnostic Part 3 — The 4-Quadrant Site Expansion Matrix

Quadrant 1

Low Candidate Volume + Strong Conversion

Diagnosis: Capacity / reach constrained

Likely actions:

• add sites,
• add geography,
• expand provider referral networks,
• add recruitment channels. Site expansion fit: HIGH

Quadrant 2

High Candidate Volume + Strong Conversion

Diagnosis: Throughput constrained

Likely actions:

• increase capacity,
• improve scheduling,
• add staff,
• potentially add sites if existing sites are saturated.

Site expansion fit: MEDIUM to HIGH

Quadrant 3

High Candidate Volume + Weak Conversion

Diagnosis: Conversion constrained

Likely actions:

• improve matching,
• reduce screen failure,
• fix site handoffs,
• improve data access,
• improve consent,
• reduce participant burden.

Site expansion fit: LOW

Quadrant 4

Low Candidate Volume + Weak Conversion

Diagnosis: Both supply and conversion constrained

Likely actions: Fix conversion first enough to understand true demand.

Then expand capacity selectively.

Site expansion fit: LOW initially

9. Diagnostic Part 4 — Hidden Cost of Adding Sites

Before adding sites, estimate the additional operational burden.

A new site may create:

• feasibility effort,
• contracting effort,
• startup cost,
• activation time,
• training,
• SIV workload,
• monitoring,
• data management,
• quality oversight,
• communication overhead,
• payment administration,
• reporting complexity,
• site support tickets.

The key question is not:

“How much does another site cost?”

It is:

“How many additional randomized participants will this site produce?”

The relevant economic measure is:

incremental cost per additional randomized participant.

10. Diagnostic Part 5 — Site Productivity Check

Before opening new sites, rank current sites by:

• candidates identified,
• candidates contacted,
• pre-screen pass rate,
• screen pass rate,
• randomized patients,
• median response time,
• coordinator workload,
• dropout rate,
• payment/reimbursement issues.

Look for:

High-volume / high-conversion sites

Model their workflow.

High-volume / low-conversion sites

Investigate leakage.

Low-volume / high-conversion sites

Potentially strong sites with insufficient reach.

Low-volume / low-conversion sites

Do not replicate this pattern.

11. Diagnostic Part 6 — The Site Expansion Decision Tree

Question 1

Are current sites generating enough potential candidates?

No Go to Question 2.

Yes

Go to Question 3.

Question 2

Do current candidates convert well?

Yes

Likely supply/capacity problem.

Site expansion may be justified.

No

Supply and conversion are both weak.

Fix conversion enough to establish a reliable baseline first.

Question 3

Are likely eligible candidates moving quickly through site workflows?

No

Fix site conversion/latency.

Yes

Go to Question 4.

Question 4

Are sites operating at realistic capacity?

Yes

Add capacity selectively. No

Improve existing site throughput before expansion.

12. Diagnostic Part 7 — Seven Questions Before Adding a Site

Before approving a new site, answer:

1.

What specific constraint will this site solve?

2.

How many additional likely eligible patients can it access?

3.

What is the site's expected conversion rate?

4.

How long until the site is productive?

5.

What additional monitoring and operational cost will it create?

6.

Are existing sites losing candidates for reasons unrelated to capacity?

7.

What is the expected incremental cost per randomized participant?

If those answers are unclear, expansion may be premature.

If the study is genuinely capacity constrained, additional sites can be the right move.

If the study is conversion constrained, the same investment may create more:

• screen failures,
• site workload,
• coordination,
• and cost.

Use the downloadable decision matrix with your Clinical Operations and Site Strategy teams.

Download the Site Expansion Decision Matrix

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BEFORE YOU ADD ANOTHER SITE

The Enrollment Capacity vs Conversion Diagnostic A decision pack for CRO Clinical Operations, Patient Recruitment and Site Strategy teams.

PAGE 2 — Quick Diagnostic

Step 1 — Patient Supply

• Current sites lack sufficient eligible patient volume
• Existing candidates convert well
• Existing site response times are strong
• New geography would materially increase reach

If mostly checked:

Capacity may be the problem.

Step 2 — Conversion

• Candidate volume is already healthy
• Screen failure is high
• Site response is slow
• Missing clinical evidence delays progression
• Consent slows candidates
• Participant burden causes drop-off
• Site conversion varies significantly

If several are checked:

Conversion is likely part of the problem.

PAGE 3 — 4-Quadrant Matrix

Strong Conversion Weak Conversion

High Candidate Volume Throughput constraint Conversion constraint

Low Candidate Volume Supply constraint Supply + conversion constraint

Interpretation Supply constraint: expand reach/capacity

Throughput constraint: increase operational capacity

Conversion constraint: fix handoffs before scaling

Both: stabilize conversion first, then expand selectively

PAGE 4 — Site Productivity Table

Site Candidate Pre-screen Screen Randomize Median Response s Pass Pass d Time

Site 1

Site 2

Site 3

Site 4

Site 5

Best-performing site:

What does it do differently?

Lowest-performing site:

Main constraint:

PAGE 5 — Expansion Economics New Site

Expected startup/activation cost: __________

Expected ongoing operational cost: __________

Expected eligible patients: __________

Expected randomized participants: __________

Months to productivity: __________

Estimated incremental cost per randomized participant:

PAGE 6 — Decision

Primary constraint

• Capacity
• Candidate quality
• Site throughput
• Screen failure
• Data access
• Consent
• Participant burden
• Multiple constraints

Should we add sites now?

• Yes
• No
• Selectively
• More diagnosis required

Why?

What should be fixed first?

Compare the Cost of Expansion Against the Cost of Leakage.

Before adding more capacity, calculate what the existing participant journey is already costing.

The Cost-per-Randomized-Patient Leakage Calculator estimates the impact of:

• screen failures,
• site/coordinator workload,
• enrollment delays,
• manual handoffs,
• participant payment friction,
• and conversion leakage.