# st: need mini tutorial in ttest result reading

 From "Ada Ma" <[email protected]> To [email protected] Subject st: need mini tutorial in ttest result reading Date Mon, 05 May 2003 15:23:20 +0000

Hi Statalisters,

I've been staring at the results for days and read the related part of the Stata manual 10 times or more and I'm still confused. I want to find out whether the results tell me that I can reject these hypostheses:

H0: mean(he) = mean(hexo) [HA: mean(he)~=mean(hexo)]
H0: sd(he) = sd(hexo) [HA: sd(he)~=sd(hexo)]

Does the following results tell me that I can can reject both HA and thus accept H0? Is it that the larger is the P figure, the more likely I'll have to accept HA?

. ttest LFShe=LFShePOT if regwk==1, unpaired

Two-sample t test with equal variances

------------------------------------------------------------------------------
Variable | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval]
---------+--------------------------------------------------------------------
LFShe | 560 9.520129 .2146156 5.078732 9.098578 9.941681
LFShePOT | 560 8.862436 .2016839 4.772713 8.466285 9.258587
---------+--------------------------------------------------------------------
combined | 1120 9.191283 .1475172 4.93687 8.901841 9.480724
---------+--------------------------------------------------------------------
diff | .6576928 .2945102 .0798378 1.235548
------------------------------------------------------------------------------
Degrees of freedom: 1118

Ho: mean(LFShe) - mean(LFShePOT) = diff = 0

Ha: diff < 0 Ha: diff ~= 0 Ha: diff > 0
t = 2.2332 t = 2.2332 t = 2.2332
P < t = 0.9871 P > |t| = 0.0257 P > t = 0.0129
. sdtest LFShe=LFShePOT if regwk==1

Variance ratio test

------------------------------------------------------------------------------
Variable | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval]
---------+--------------------------------------------------------------------
LFShe | 560 9.520129 .2146156 5.078732 9.098578 9.941681
LFShePOT | 560 8.862436 .2016839 4.772713 8.466285 9.258587
---------+--------------------------------------------------------------------
combined | 1120 9.191283 .1475172 4.93687 8.901841 9.480724
------------------------------------------------------------------------------

Ho: sd(LFShe) = sd(LFShePOT)

F(559,559) observed = F_obs = 1.132
F(559,559) lower tail = F_L = 1/F_obs = 0.883
F(559,559) upper tail = F_U = F_obs = 1.132

Ha: sd(1) < sd(2) Ha: sd(1) ~= sd(2) Ha: sd(1) > sd(2)
P < F_obs = 0.9290 P < F_L + P > F_U = 0.1420 P > F_obs = 0.0710

Lots of thanks in advance.
yours,
Dept of Economics
Univ of Aberdeen
[email protected]

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