Dear Statalisters,
I am having difficulty interpreting output from two -signtest- commands.
-----
* (1) Testing distribution of variable in 1995 and 2000 are equal
. signtest rtotshare95=rtotshare00
Sign test
sign | observed expected
-------------+------------------------
positive | 9646 13135
negative | 16624 13135
zero | 0 0
-------------+------------------------
all | 26270 26270
One-sided tests:
Ho: median of rtotsha~95 - rtotshare00 = 0 vs.
Ha: median of rtotsha~95 - rtotshare00 > 0
Pr(#positive >= 9646) =
Binomial(n = 26270, x >= 9646, p = 0.5) = 1.0000
Ho: median of rtotsha~95 - rtotshare00 = 0 vs.
Ha: median of rtotsha~95 - rtotshare00 < 0
Pr(#negative >= 16624) =
Binomial(n = 26270, x >= 16624, p = 0.5) = 0.0000
Two-sided test:
Ho: median of rtotsha~95 - rtotshare00 = 0 vs.
Ha: median of rtotsha~95 - rtotshare00 != 0
Pr(#positive >= 16624 or #negative >= 16624) =
min(1, 2*Binomial(n = 26270, x >= 16624, p = 0.5)) = 0.0000
-----
* (2) Testing distribution of variable in 2000 and 2004 are equal
. signtest rtotshare00=rtotshare04
Sign test
sign | observed expected
-------------+------------------------
positive | 15276 13135
negative | 10994 13135
zero | 0 0
-------------+------------------------
all | 26270 26270
One-sided tests:
Ho: median of rtotsha~00 - rtotshare04 = 0 vs.
Ha: median of rtotsha~00 - rtotshare04 > 0
Pr(#positive >= 15276) =
Binomial(n = 26270, x >= 15276, p = 0.5) = 0.0000
Ho: median of rtotsha~00 - rtotshare04 = 0 vs.
Ha: median of rtotsha~00 - rtotshare04 < 0
Pr(#negative >= 10994) =
Binomial(n = 26270, x >= 10994, p = 0.5) = 1.0000
Two-sided test:
Ho: median of rtotsha~00 - rtotshare04 = 0 vs.
Ha: median of rtotsha~00 - rtotshare04 != 0
Pr(#positive >= 15276 or #negative >= 15276) =
min(1, 2*Binomial(n = 26270, x >= 15276, p = 0.5)) = 0.0000
-----
My first question is: am I supposed to use a one sided test or the
two-sided test? My inclination is to use the one sided test given my
priors concerning the relationships between the variables.
My second question is: is it usual to see values of either 0.0000 or
1.0000 in this test, or is this more a function of my particular
variables in this dataset?
Any assistance would be appreciated.
Reza
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