# [Rd] R-1.9.0 Beta print.power.htest problem?

Marc Schwartz MSchwartz at MedAnalytics.com
Wed Mar 31 20:44:25 CEST 2004

```Hi all,

I just used power.t.test() in Version 1.9.0 beta (2004-03-31) today
under FC1.

The following is the output:

> power.t.test(delta = .5, power = .95, type = "paired")
\$n
 53.94062

\$delta
 0.5

\$sd
 1

\$sig.level
 0.05

\$power
 0.95

\$alternative
 "two.sided"

\$note
 "n is number of *pairs*, sd is std.dev. of *differences* within
pairs"

\$method
 "Paired t test power calculation"

attr(,"class")
 "power.htest"

The following is the output from Version 1.8.1 Patched (2004-03-31):

>  power.t.test(delta = .5, power = .95, type = "paired")

Paired t test power calculation

n = 53.94062
delta = 0.5
sd = 1
sig.level = 0.05
power = 0.95
alternative = two.sided

NOTE: n is number of *pairs*, sd is std.dev. of *differences* within
pairs

I have reviewed the following code for print.power.htest in power.R in
both 1.8.1 patched and the 1.9.0 Beta and do not see any differences, so
I am guessing that there is a methods issue here:

print.power.htest <-
function(x, ...)
{
cat("\n    ", x\$method, "\n\n")
note<-x\$note
x[c("method","note")] <- NULL
cat(paste(format.char(names(x), width=15, flag="+"),
format(x), sep=" = "),sep="\n")
if(!is.null(note))
cat("\n", "NOTE:", note, "\n\n")
else
cat("\n")
}

Using 'methods(print)' in 1.8.1 patched, print.power.htest is listed,
while it is not listed in 1.9.0 beta, which would seem to reinforce a
methods problem.

The 1.8.1 patched NAMESPACE file for 'ctest' lists:

S3method(print, power.htest)

However, the NAMESPACE file for 'stats' in 1.9.0 Beta does not, so I am
guessing that this is the source of the problem?

Thanks,

Marc Schwartz

```