st: ttest error message

[Xixi Lin <winnielxx@gmail.com>]

Hi,

I am using the following ttest code; however it shows the error
message:1 group found, 2 required-----what does it mean?

Here is my code:
foreach x in x1 x2 x3 x4 x5 {
foreach z of numlist 2/120 {
foreach j of numlist 10 15 20 25 30 35 40 45 50 55 {
    qui ttest Return if inlist(group_`x',1,10) & Period==`z' &
Sector==`j', by(group_`x') unequal
    display "`x'"   "Period "  "`z'"  "Sector " "`j'"  `r(p_l)'
`r(p)'  `r(p_u)'
 }
}
}

Any help is appreciated!

Thanks,
Xixi Lin
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/faqs/resources/statalist-faq/
*   http://www.ats.ucla.edu/stat/stata/