---------- Forwarded message ----------
From: HelponR <suncertain@gmail.com>
Date: Dec 19, 2006 9:28 AM
Subject: nonparametric significance test for one sample
To: r-help <r-help@stat.math.ethz.ch>

Hello, Gurus:

I tried to test if the sample mean of a dataset is zero.

The data has 1500 numbers with a lot of zeros and some small
positive numbers. The data range on [0,1] but the distribution is unknown.
It is zero inflated anyway.

I tried to use the  Wilcoxon Signed Ranks test. But I read from this website
that it does assume the population pdf is symmetric.

http://www.cas.lancs.ac.uk/glossary_v1.1/nonparam.html#wsrt
"The Wilcoxon Signed Ranks test does not require the assumption that the
population is normally distributed. In many applications, this test is used
in place of the one sample
t-test<http://www.cas.lancs.ac.uk/glossary_v1.1/hyptest.html#1sampt>when
the normality assumption is questionable. It is a more powerful
alternative to the sign test, but does assume that the population
probability distribution is symmetric."

I wonder if wilcox.test( ) in R also assumes the symmetric pdf?

I checked the sign test too. But "the sign *test* is not *testing
equality*of population
"

If wilcox.test() cannot work for my data, I wonder if you could suggest a
kind of test? I already tried t-test (assume normality) but I want to find
something else.

Many thanks!

S

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