Dear Statalist Colleagues,
This might be a simple question but I cannot reconcile the following results.
The question is "Are the estimates for year 1 and 3 statistically different?
year estimate st.error 95% conf interval
year1 .484721 .015637 .454068 .5153741
year2 .4128893 .0145616 .3843443 .4414343
year3 .4556235 .0138994 .4283765 .4828704
1. Using the 95% confidence interval that I obtained:
Year 1 and year 3 confidence intervals overlap thus year 1&3 estimates are not statistically different at the 95% level.
2. Using ttesti they are statistically different with 99% confidence:
. ttesti 2398 .484721 .015637 2399 .4556235 .0138994
Two-sample t test with equal variances
------------------------------------------------------------------------------
| Obs Mean Std. Err. Std. Dev. [95% Conf. Interval]
---------+--------------------------------------------------------------------
x | 2398 .484721 .0003193 .015637 .4840948 .4853472
y | 2399 .4556235 .0002838 .0138994 .455067 .45618
---------+--------------------------------------------------------------------
combined | 4797 .4701692 .0002996 .0207488 .4695819 .4707565
---------+--------------------------------------------------------------------
diff | .0290975 .0004272 .02826 .029935
------------------------------------------------------------------------------
Degrees of freedom: 4795
Ho: mean(x) - mean(y) = diff = 0
Ha: diff < 0 Ha: diff != 0 Ha: diff > 0
t = 68.1143 t = 68.1143 t = 68.1143
P < t = 1.0000 P > |t| = 0.0000 P > t = 0.0000
Which one is the correct? What am I not interpreting right?
Thank you in advance.
Sincerely,
Alla
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