Represents the issue of selection bias in a clinical trial.
Usage
selBias(type, eta, method, alpha = 0.05)
Arguments
type
character string, should be one of "CS" or "DS", see
Details.
eta
numeric specifying the magnitude of selection bias.
method
character string, should be one of "sim" or "exact", see
Details.
alpha
significance level.
Details
Selection bias can be an issue in the design of a clinical trial. The
selBias function is a constructor function
for an S4 object of the class selBias representing the issue of
third order selection bias in a clinical trial. It supports two possible modes,
method="sim" and method="exact". This representation is
particularly useful in interaction with the assess function.
method="sim"
Represents the simulated type-I-error rate given
the level alpha, the selection effect eta and the biasing
strategy type. When calling assess for a selBias object
with method="sim", one test decision is computed for each sequence of
randSeq. The type-I-error rate (power) is the proportion of falsely
(correctly) rejected null hypotheses.
method="exact"
Represents the exact type-I-error proabability
given the level alpha, the selection effect eta and the
biasing strategy type. When calling assess for a selBias
object with method="exact", the exact p-value of each
randomization sequence is computed. So far, this is only supported for
normal endpoints. Then the type-I-error probability is
the sum of the corresponding quantiles of the doubly noncentral t-distribution.
Value
S4 object of class selBias, a formal representation of the
issue of selection bias in a clinical trial.
References
D. Blackwell and J.L. Hodges Jr. (1957) Design for the control of
selection bias. Annals of Mathematical Statistics, 25, 449-60.
M. Proschan (1994) Influence of selection bias on the type-I-error rate
under random permuted block designs. Statistica Sinica, 4, 219-31.
See Also
Compute exact or simulated type-I-error: assess.
Other issues: chronBias,
combineBias, corGuess,
imbal, issue,
setPower