one-tail test command

[Yahya Ghazali]

Dear All

I have a quick question here regarding one-tail test command in Stata.

My alternate hypothesis predicts that DSTATE<0.

The regression results show that DSTATE has a negative coefficient -0.245 with p-value 0.000 (this is the standard regression p-value i.e two-tailed).

Could you please suggest a command which can test for one-tailed test as per my alternative hypothesis?

Many thanks

Yahya

[Carlo Lazzaro]

Yahya:
the following toy-example might be useful:

. sysuse auto.dta
(1978 Automobile Data)

. ttest price, by(foreign) unequal

Two-sample t test with unequal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
Domestic |      52    6072.423    429.4911    3097.104    5210.184    6934.662
 Foreign |      22    6384.682    558.9942    2621.915     5222.19    7547.174
---------+--------------------------------------------------------------------
combined |      74    6165.257    342.8719    2949.496    5481.914      6848.6
---------+--------------------------------------------------------------------
    diff |           -312.2587    704.9376               -1730.856    1106.339
------------------------------------------------------------------------------
    diff = mean(Domestic) - mean(Foreign)                         t =  -0.4430
Ho: diff = 0                     Satterthwaite's degrees of freedom =  46.4471

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3299         Pr(|T| > |t|) = 0.6599          Pr(T > t) = 0.6701

. di 1-ttail(46.4471,-0.4430)
.32991111

. di ttail(46.4471,-0.4430)
.67008889

.