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Data Collection Duration Calculator

Work out data collection duration instantly with clear inputs, formula shown and shareable results.

About Data Collection Duration Calculator

Recruitment duration depends on the screening funnel, not just the target. Needing 240 participants with a 25% screen failure rate means screening 320, and at twelve screened a week that is 26.7 weeks - just over six months, at an effective enrolment rate of nine a week. Underestimating the failure rate is the classic cause of trial delay.

Formulas

Participants to screen

screened = target / (1 - screen failure rate)

Duration

weeks = participants to screen / screening rate per week

Worked example

With the default values below, Data Collection Duration Calculator returns Weeks Of Recruitment Required of 26.7. Change any input above and every figure here is recalculated in your browser.

Inputs used

Target sample sizeminimum 1
240
Participants recruited per weekminimum 0.1
12
Screening failure rateaccepts 0–95 %
25 %

Results

Weeks Of Recruitment Required
26.7 weeks
Participants To Screen
320
Months Required
6.1
Effective Enrolments Per Week
9.00

Step by step

  1. 1Values used
  2. 2Participants to screen
  3. 3Duration
  4. 4Weeks Of Recruitment Required= 26.7 weeks
  5. 5Participants To Screen= 320
  6. 6Months Required= 6.1
  7. 7Effective Enrolments Per Week= 9.00

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why do trials underestimate recruitment time?

Because pilot rates come from enthusiastic early sites. Recruitment typically slows once the easiest eligible participants are exhausted.

Should I plan for over-recruitment?

Yes. Recruiting 10-15% above target protects the analysis against withdrawals and protocol deviations.

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