powEx {sse} | R Documentation |
A function for constructing an object of class power used for drawing an example in a sensitivity plot and for estimating the sample size.
powEx(x, theta, xi = NA, endpoint = NA, power = 0.9, drop = 0, method = c("default", "lm", "step"), lm.range = NA, forceDivisor = FALSE)
x |
An object of class powCalc. |
theta |
a numeric value indicating for which |
xi |
a numeric value, as |
endpoint |
Object of class |
power |
Object of class |
method |
Defining the method how the sample size for the is
calculated. |
lm.range |
The range of evaluations that are used for estimating
the sample size if the |
drop |
Object of class |
forceDivisor |
If |
For method equal to "lm"
a linear model is fit as
lm(sample.size ~ transformed(power)) with all data where theta, and xi
are equal to the theta and xi of the example and within the
power-range as defined by the argument lm.range
. This model is
then used for predicting the sample size. Always inspect the result
using inspect
!
The method "step" returns the last element in the sequence of sample sizes - power pairs, sorted with decreasing power, where the power is above the power defined for the example.
An object of class power.
In older verstions of the package: The function merge
was
used together with an object of class powEx to form an
object of class power.
## defining the range of n and theta to be evaluated psi <- powPar(theta = seq(from = 0.5, to = 1.5, by = 0.1), n = seq(from = 20, to = 60, by = 2), muA = 0, muB = 1) ## defining a power-function powFun <- function(psi){ power.t.test(n = n(psi)/2, delta = pp(psi, "muA") - pp(psi, "muB"), sd = theta(psi) )$power } ## evaluating the power-function for all combinations of n and theta calc <- powCalc(psi, powFun) ## adding example at theta of 1 and power of 0.9 pow <- powEx(calc, theta = 1, power = 0.9) ## drawing the power plot with 3 contour lines plot(pow, xlab = "Standard Deviation", ylab = "Total Sample Size", at = c(0.85, 0.9, 0.95)) ## changing the estimation method pow2 <- powEx(calc, theta = 1, power = 0.9, method = "lm") ## drawing an inspection plot inspect(pow2)