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The parameters to calculate power
and sample size
Number of periods. The number of time periods in
which patients are to be enrolled and followed, usually expressed in months or years. The
hazard is constant within each period.
Control event rate. The conditional
probability of having an event, given having survived the previous periods. In the
"Proportional hazards" calculator, only a single entry is allowed, which is the
constant conditional probability. In the "Non-proportional hazards" calculator,
the number of conditional probabilities specified must match number of periods in the
study. Each entry can be a unique probability. The rates entered must be separated by
spaces.
Hazard ratio, treated-to-control. The ratio of
the hazard rates in each period. In the "Proportional hazards" calculator, only
a single entry is allowed, which represents the constant ratio of the hazard rates in each
period for the treated group to the control group. In the "Non-proportional
hazards" calculator, the number of hazard ratios specified must match the number of
periods in the study. Each entry can be a unique hazard ratio. The ratios entered must be
separated by spaces.
Two-sided type I error. Probability of falsely
rejecting the null hypothesis.
Test statistic. The test statistic used to
calculate power or sample size. Either the standard log-rank test or the binomial test can
be used.
Patient entry. Describes how patients enter
the study. Patients either enter simultaneously or uniformly over an accrual period.
Number of time periods for uniform patient entry.
The number of periods for patient recruitment. Must be specified if patient entry is not
simultaneous.
Ratio of sample size,
control:treated. The
number of patients assigned to the control group for each patient assigned to the treated
group. In general, if R=n/m, then the total sample size N is n(R+1)/R, where n and m are
the sample sizes of the control & treated groups, respectively.
Lag in treatment effect. The number of periods
to achieve full treatment effect. An entry of 0 indicates full treatment effect is
achieved immediately. In the "Non-proportional hazards" calculator, it adjusts
the event rate for crossovers. If 0 is entered, then patients return to the efficacy level
comparable to the level in the opposite group immediately after crossover. This number
should less than or equal to the number of periods in the study.
Lagged effect of drop-out. Describes how the
treatment vanishes for those who cross over to the control group. A gradual lagged effect
describes the treatment level of the those who drop out of the treated group to return to
the level of the control group in the same way the treatment reached its full effect. An
immediate effect describes the treatment level vanishing completely when a patient drops
out of the treated group.
Rate of crossover to treated in each period.
The conditional probability of patients crossing over to the treatment assigned to the
treated group, given having complied with the treatment assigned in the previous periods.
The number of probabilities specified must match the number of periods in the study. The
probabilities entered must be separated by spaces.
Rate of crossover to control in each period.
The conditional probability of patients crossing over to the treatment assigned to the
control group, given having complied with the treatment assigned in the previous periods.
The number of probabilities specified must match the number of periods in the study. The
probabilities entered must be separated by spaces.
Loss to follow-up rate in each period. The
conditional probability of patients becoming lost to follow-up, given having been followed
in the previous periods. The number of probabilities specified must match the number of
periods in the study. The probabilities entered must be separated by spaces.
Power. Probability of correctly rejecting the
null hypothesis under the specified assumptions.
Total sample size.
The sum of the sample sizes in the control and treated groups. |