CRTpower {CRTspat} | R Documentation |
Power and sample size calculations for a CRT
Description
CRTpower
carries out power and sample size calculations for CRTs.
Usage
CRTpower(
trial = NULL,
locations = NULL,
alpha = 0.05,
desiredPower = 0.8,
effect = NULL,
yC = NULL,
outcome_type = "d",
sigma2 = NULL,
denominator = 1,
N = 1,
ICC = NULL,
cv_percent = NULL,
c = NULL,
sd_h = 0
)
Arguments
trial |
dataframe or |
locations |
numeric: total number of units available for randomization (required if |
alpha |
numeric: confidence level |
desiredPower |
numeric: desired power |
effect |
numeric: required effect size |
yC |
numeric: baseline (control) value of outcome |
outcome_type |
character: with options -
|
sigma2 |
numeric: variance of the outcome (required for |
denominator |
numeric: rate multiplier (for |
N |
numeric: mean of the denominator for proportions (for |
ICC |
numeric: Intra-cluster correlation |
cv_percent |
numeric: Coefficient of variation of the outcome (expressed as a percentage) |
c |
integer: number of clusters in each arm (required if |
sd_h |
standard deviation of number of units per cluster (required if |
Details
Power and sample size calculations are for an unmatched two-arm trial. For counts
or event rate data the formula of Hayes & Bennett, 1999 is used. This requires as an input the
between cluster coefficient of variation (cv_percent
). For continuous outcomes and proportions the formulae of
Hemming et al, 2011 are used. These make use of
the intra-cluster correlation in the outcome (ICC
) as an input. If the coefficient of variation and not the ICC is supplied then
the intra-cluster correlation is computed from the coefficient of variation using the formulae
from Hayes & Moulton. If incompatible values for ICC
and cv_percent
are supplied
then the value of the ICC
is used.
The calculations do not consider any loss in power due to spillover, loss to follow-up etc..
If geolocations are not input then power and sample size calculations are based on the scalar input parameters.
If a trial dataframe or 'CRTsp'
object is input then this is used to determine the number of locations. If this input object
contains cluster assignments then the numbers and sizes of clusters in the input data are used to estimate the power. If buffer zones have been specified
then separate calculations are made for the core area and for the full site.
The output is an object of class 'CRTsp'
containing any input trial dataframe and values for:
The required numbers of clusters to achieve the specified power.
The design effect based on the input ICC.
Calculations of the nominal power (ignoring any bias caused by spillover, loss to follow-up etc.)
Value
A list of class 'CRTsp'
object comprising the input data, cluster and arm assignments,
trial description and results of power calculations
Examples
{# Power calculations for a binary outcome without input geolocations
examplePower1 = CRTpower(locations = 3000, ICC = 0.10, effect = 0.4, alpha = 0.05,
outcome_type = 'd', desiredPower = 0.8, yC=0.35, c = 20, sd_h = 5)
summary(examplePower1)
# Power calculations for a rate outcome without input geolocations
examplePower2 = CRTpower(locations = 2000, cv_percent = 40, effect = 0.4, denominator = 2.5,
alpha = 0.05, outcome_type = 'e', desiredPower = 0.8, yC = 0.35, c = 20, sd_h=5)
summary(examplePower2)
# Example with input geolocations and randomisation
examplePower3 = CRTpower(trial = readdata('example_site.csv'), desiredPower = 0.8,
effect=0.4, yC=0.35, outcome_type = 'd', ICC = 0.05, c = 20)
summary(examplePower3)
}