commonbounds {ldbounds}

Commonly Used Group Sequential Boundaries

Description

'commonbounds' determines group sequential boundaries of the well-known O'Brien-Fleming and Pocock types. These can be used as guidelines for early stopping of the trial. For Haybittle-Peto type boundaries, see function 'lastbound'. Note: these are NOT the alpha-spending versions of these boundaries.

Usage

commonbounds(looks, t=(1:looks)/looks, t2=t, iuse="OF", alpha=0.05, sides=2)

Arguments

looks

A number of equally spaced analysis times.

t

a vector of analysis times, if looks is not provided. If times are provided and they are not equally spaced, there will be a warning.

t2

the second time scale, usually in terms of amount of accumulating information. By default, same as the equally spaced analysis times or the analysis times corresponding to t.

iuse

the type of bounds: O'Brien-Fleming ("OF") or Pocock ("PK") If two-sided bounds are calculated, the same type will be used for each of the two boundaries. If a vector of length two is given, the two values will be used for lower and upper bounds, respectively. Details of specification are given below.

alpha

Type I error(s). In two-sided situations, alpha can be a single value, indicating symmetric type I error control (half of alpha for each boundary). If a vector of length two is given, this corresponds to the amount allocated to the lower and upper boundaries, respectively. The total alpha must be greater than 0 and less than or equal to 1.

sides

Designates one- or two-sided bounds.

Details

This function calculates boundaries corresponding to traditional O'Brien-Fleming or Pocock boundaries. Note that these are not the alpha spending function versions of the boundaries. For those, use ldBounds.

Value

'commonbounds' returns an object of 'class' '"ldBounds"'.

For details about this object class, see the documentation for the ldBounds function.

Author(s)

Charlie Casper [e-mail]

References

Reboussin, D. M., DeMets, D. L., Kim, K. M., and Lan, K. K. G. (2000) Computations for group sequential boundaries using the Lan-DeMets spending function method. Controlled Clinical Trials, 21:190-207.

DeMets, D. L. and Lan, K. K. G. (1995) Recent Advances in Clinical Trial Design and Analysis, Thall, P. F. (ed.). Boston: Kluwer Academic Publishers.

Lan, K. K. G. and DeMets, D. L. (1983) Discrete sequential boundaries for clinical trials. Biometrika, 70:659-63.

See Also

Generic functions summary.ldBounds and plot.ldPower.

ldBounds for boundaries that use the alpha spending approach.

ldPower for exit probabilities given boundaries OR drift (effect) given power OR confidence interval OR adjusted p-value.

Examples

   ## From Reboussin, et al. (2000)

   time <- seq(0.2,1,length=5)
   obf.bd <- commonbounds(t=time)
   summary(obf.bd)
   plot(obf.bd)

   # Equivalent bounds to above
   obf.bd2 <- commonbounds(5)