Unbalanced to balanced dataset

[Taiba Chau]

Hi, I have a cross-sectional dataset with 25,899 observations. This is essentially unbalanced panel data. There are 2 waves and cover 5 countries. I was wondering if there is a way to transform this unbalanced panel data into a balanced dataset.

I started by creating an n variable that counts the number of observations for each country. I used the code:
generate n = _N
However, I do not know if this is exactly correct.

I know I would need a code that would drop the observations if they were not observed in waves 1 and 2.

Thank you

[Jared Greathouse]

If I'm understanding the question properly, you want all units in the study to have the same number of periods that they're observed for. So, Unit A has 10 periods, Unit B has 10 and Unit C can't have, say, 8 periods that they're observed for.

So, here's how we'd drop area C.

tempvar obs

qbys id: g `obs' =_N
su `obs', mean
drop if `obs' !=r(max)

In the ficticious example I gave above (note that I'm on my phone and can't literally demonstrate this), obs= 10 for A, B, and 8 for C. If we wanted to only use units that have observations for ALL periods, this is one way of doing so, and no doubt there are improvements upon what I do here.


Oh, and just a technical note: no, you don't have a cross sectional dataset, you have a longitudinal dataset/unbalanced panel (as you write below).

[Taiba Chau]

Thank you! I understand what you did. I am just wondering if what the second line of code means with id

[Carlo Lazzaro]

Taiba:

 
 quietly bysort id: generate `obs' =_N

[Jared Greathouse]

To put it in what programmers (which I guess I am) would call pseudocode, i quietly, and for each ID, generated a temporary variable called "obs", short for observations of course.

It's temporary because we presumably won't need it for anything else aside from the express purpose we're using it for. In this case, _N refers to the grand total of observations per group.

Now that I'm at my computer (was on my phone last night), we can create a simply toy for this.

clear
cls

set obs 31

egen id = seq(), f(1) t(3) b(10)

replace id = 4 in 31

qui xtset id

if r(balanced) == "unbalanced" {
di "The panel is unbalanced!!! Correcting now:"



tempvar obs

qbys id: g `obs' =_N
su `obs', mean
drop if `obs' !=r(max)
}

qui xtset id

if r(balanced) == "balanced" {
    
    di "All is well"
    
}

4 IDs in total; 3 of them are observed for 10 periods, 1 of them (ID 4) is observed for only 1 period. If we want a balanced panel, we either need to get data for those periods or get rid of the units that aren't balanced, in this case 4.


So, I xtset my data which I purposely made unbalanced. I then do tasks based on if the data are balanced. If not, (if r(balanced) is unbalanced), I find the ones that aren't balanced and delete them

And to confirm that this was successful, I re-xtset my data, And, so long as the data are NOT unbalanced (as they now shouldn't be), I tell Stata to display "All is well" if in fact everything checks out. Or put another way, if now the result is "balanced", then we continue on as normal.

[River Huang]

Dear Taiba, Please ssc install xtbalance (or xtbalance2), and check out the help file.

[Taiba Chau]

i tried the following code suggested by carlo:
quietly bysort id: generate `obs' =_N But it came with message saying two few variables specified

[Carlo Lazzaro]

Taiba:
the only aim of my previous reply was to explain Jared's abbeviations (that become frequent when you get yourself familiar with Stata)..

[Taiba Chau]

Oh understood. I still am confused. Because I have created my own unique ID for the individuals within the data. I only 2 waves of data. So would I do the same as suggested by Jared
tempvar obs qbys id: g `obs' =_N su `obs', mean drop if `obs' !=r(max)

[Taiba Chau]

I have just done this an left with only 5 observations. This is not entirely correct. The last line of code:
drop if `obs' !=r(max)
I think needs to be something else

Just wondering if there is another way to go about this. if I do not have an id variable

[Jared Greathouse]

Why not use the unique ID you speak of in #9? I guess my question for you is how are you xtsetting your data? That is, what're your panel and time variables?

If you follow my example from #5, that's one way of doing it. If you're getting "too few variables" from

tempvar obs
qbys id: g `obs' =_N
su `obs', mean
drop if `obs' !=r(max)

this tells me you either didn't declare your tempvar or you didn't use your ID variable in the qbys prefix.

What we now need to see is the exact code you ran- show us the code you ran in [CODE] Code [/CODE] delimiters, and paste the output here, including the place where Stata spits an error out and the specific error Stata issues.