Clinical Trial Sample Size Model
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Determine the total number of participants required for a clinical trial accounting for effect size uncertainty and dropout risk.
NOTEAbout This Model
## Determine the total number of participants required for a clinical trial accounting for effect size uncertainty and dropout risk. This model estimates **Total Trial Enrollment** based on uncertain inputs: Effect Size, Dropout Rate. Run the simulation to see the distribution of possible outcomes.
VARIABLEEffect Size
triangular(0.2, 0.5, 0.8)
Cohen's d: 0.2 is small, 0.5 is medium, 0.8 is large. We model the uncertainty in expected treatment impact.
effect_size
VARIABLEDropout Rate
beta(3.5, 16.5)
Typical clinical trial dropout rates range from 5% to 30% depending on study duration and complexity.
dropout_rate
FORMULABase Sample Size Per Group
2 * (pow(1.96 + 0.84, 2) / pow(effect_size, 2))
Calculate required sample size per group for a two-sample t-test using the standard approximation formula.
base_sample_size_per_group
FORMULAAdjusted Sample Size Per Group
base_sample_size_per_group / (1 - dropout_rate)
Adjust group sample size for anticipated dropouts to maintain statistical power.
adjusted_sample_size_per_group
FORMULATotal Trial Enrollment
ceil(adjusted_sample_size_per_group * 2)
Total subjects needed across both treatment and control arms, rounded up.
total_trial_enrollment
OUTPUTTotal Trial Enrollment
total_trial_enrollment
Total participants needed across treatment and control groups, adjusted for expected dropouts. Larger trials increase statistical power but cost more—find the balance for your budget.
What is Carlo?
Carlo is a visual tool for Monte Carlo simulation. Model uncertainty by dragging probability distributions, connecting them visually, and running thousands of scenarios instantly.