quartiles

[ASMA ALSHAREEF]

I want to do table like this but i dont know how to do it
can any one help me with codes?

[Joro Kolev]

You can calculate quartiles by variables such as year using the user contributed function -egen, xtile()- from the package Egenmore.

[Ken Chui]

sysuse auto, clear
xtile qmpg = mpg, nq(4)
* Table:
tabstat price, stat(mean p50 min max) by(qmpg)
* t-test between lowest and highest:
ttest price if inlist(qmpg, 1, 4), by(qmpg)

[ASMA ALSHAREEF]

how i make the table like if i found the quartles then find the t-test how i make the table

[Ken Chui]

One way is to copy the output as table, paste onto Excel and manually do the editing/formatting. This may be better if this is just a one-time task.

To automate the process, one way is to do that through -putexcel-:

help putexcel

Also, check out this very useful series of blog posts on laying out the results in Excel. Part 1, part 2, part 3.

[ASMA ALSHAREEF]

whta is 1 and 4 here (ttest price if inlist(qmpg, 1, 4), by(qmpg)) and when i take t-test for the size give me this ( . * t-test between lowest and highest: . ttest size if inlist(size_4, 1, 4), by(size_4) 1 group found, 2 required r(420);

[Ken Chui]

whta is 1 and 4 here (ttest price if inlist(qmpg, 1, 4), by(qmpg)) and when i take t-test for the size give me this ( . * t-test between lowest and highest: . ttest size if inlist(size_4, 1, 4), by(size_4) 1 group found, 2 required r(420);

inlist(qmpg, 1, 4) means "only if qmpg == 1 or qmpg == 4". This two groups were kept because the t-test only used the lowest and highest groups of the four (according to the description above the table in post #1).

[ASMA ALSHAREEF]

Thank you Ken
what if the quartiles are constructed each year,?

[Ken Chui]

Usually we can use the -by()- option, but xtile is special that it does not work with by(), so you'd probably have to create a new quartile variable for each year using -if-. For example:

xtile new_var19 = old_var if year == 2019 , nq(4)
xtile new_var20 = old_var if year == 2020 , nq(4)
xtile new_var21 = old_var if year == 2021 , nq(4)

Then you can combine them back into one variable. But remember to label them clearly saying that it's year-based quartlies.

For example, this would result in an error:

clear
sysuse auto
bysort foreign: xtile new = mpg, nq(4)

But this would work:

clear
sysuse auto
xtile q_domestic = mpg if foreign == 0, nq(4)
xtile q_local = mpg if foreign == 1, nq(4)
egen q_combined = rowtotal(q_domestic q_local)