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# ztest: picking up wrong value labels in its output?

 From "Edmond Ng" To Subject ztest: picking up wrong value labels in its output? Date Fri, 18 Jul 2003 19:00:41 +0100

```Dear all,

I am just wondering if I am right to point out that 'ztest' seems to
use rather odd labels in its output. My outcome variable is a binary
(0/1) variable representing low birth weight and the explanatory, ht2,
is also a binary (0/1) variable. The null hypothesis shown in the output
is as follows.

Ho: Pr(lbw = 1) - Pr(y = 1) = diff = 0

The labels used in the brackets seem odd. Should Pr( ..) represent the
probability of being a case (low birthweight) in this case, it would
have made more sense if the labels within the brackets  were "ht2=1" and
"ht2=0", respectively. Can anyone shed any light on this oddity please?
Many thanks in advance.

Edmond

. ztest lbw, by(ht2)

Two-sample z test

------------------------------------------------------------------------------
Variable |     Obs        Prop    Std. Err.   Std. Dev.   [95% Conf.
Interval]
---------+--------------------------------------------------------------------
lbw |     542     .097786    .0127583    .2970251    .0727801
.1227918
y |      99    .2727273    .0447605    .4453618    .1849982
.3604563
---------+--------------------------------------------------------------------
combined |     641     .124805    .0361227    .3304977    .0540058
.1956042
---------+--------------------------------------------------------------------
diff |     641   -.1749413    .0361227    .3304977   -.2457405
-.1041421
------------------------------------------------------------------------------

Ho: Pr(lbw = 1) - Pr(y = 1) = diff = 0

Ha: diff < 0               Ha: diff ~= 0              Ha: diff >
0
z =  -4.8430                z =  -4.8430              z =
-4.8430
P < z =   0.0000          P > |z| =   0.0000          P > z =
1.0000

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```

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