I'm attempting to do a power analysis on occurrence data (0.0 -> 1.0; i.e. the number a sites a species was present out of the total number of sites sampled for a single season), where I want to see what power I have to detect a change of 20% (two-sided test) from one season's worth of data to the next. For example, "...Dry season 2023 could have a proportion of 0.6, what power do I have to detect a 20% change (up or down) from 0.6 for next year?" The data comes from the same 47 sites each season (paired data) and I'm using the package 'pwrss'. My questions are:
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Is this a one or a two-sample question?
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What values are my "p/p1" and "p0/p2" in the code?
Since I think this is a one-sample test, according to the documentation, "p" = the expected proportion, but what is that if I'm doing a two-sided test (it could + or - 20% of my record occurrence)? Is "p0" = my proportion I calculated from 1 season's worth of data ("constant to be compared (a proportion)" as defined in the documentation) or it the change I expect to see?
# One-sample version:
pwrss.z.prop(p = 0.6, p0 = ?,
alpha = 0.05,
power = NULL,
n = 47,
alternative = "not equal",
arcsin.trans = TRUE)
# 2-sample version:
pwrss.z.2props(p1 = 0.6, p2 = ?,
alpha = 0.05,
power = NULL,
n = 47,
alternative = "not equal",
arcsin.trans = TRUE)