st: need mini tutorial in ttest result reading

["Ada Ma" <pelikan_4001@hotmail.com>]

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,
Ada Ma
Dept of Economics
Univ of Aberdeen
Pelikan_4001@hotmail.com

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