missing data in panel data

[Huda Amin]

Hi,

I am working on panel data for the period from 2012 to 2020 with 2529 observations (. I need help dealing with missing data for variables (dependent, independent, control and dummy). My panel data is unbalanced and sometimes I find the missing data, in the beginning, middle and end. How can I solve this issue, please?

xtset id year
panel variable: id (unbalanced)
time variable: year, 2012 to 2020, but with gaps
delta: 1 unit

there are missing value in some variables as shown below

id	year	W_ROA	CEO_DUALITY	YEAR OF INC
17	2012	9.84	.	2007
17	2013	7.66	.	2007
17	2014	13.3	.	2007
17	2015	.	.	2007
17	2016	.	.	2007
17	2017	9.78	.	2007
17	2018	15.25	.	2007
17	2019	11.78	.	2007
17	2020	13.87	.	2007
18	2012	.	.	2015
18	2013	.	.	2015
18	2014	.	.	2015
18	2015	.	.	2015
18	2016	.	0	2015
18	2017	2.81	0	2015
18	2018	3.25	0	2015
18	2019	3.65	1	2015
18	2020	3.97	1	2015

I would like to ask how can I fill in the missing values (should I take into account the date of incorporation).

[Muhammad Ramzan]

Hi you can use Stata interpolate ipolate option to fill in the missing values
Please see this file
https://www.stata.com/manuals/dipolate.pdf

[Carlo Lazzaro]

Huda:
even though panel attrition is frequent in longitudinal studies, you should investigate whether the missingness is informative or not before considering any interpolation/imputation strategy..

[Huda Amin]

Thanks Muhammad and Carlo.
I know the interpolation will solve the problem, but my question is how can I use it only if there are gaps in the middle or in the end ,some firms were established after 2012 so I don't want to fill in missing values before establishing.

Can you suggest a suitable way to solve this issue?

[Carlo Lazzaro]

Huda:
the safest approach is to live with your unbalanced panel dataset.
Obviously, this approach comes at the cost of ending up with a very small sample to use for your regression.
That said, if some firms were established after a given year, there's nothing to interpolate or impute before that year.

[Huda Amin]

That's exactly what I mean. Can I use the following code to fill the gap after the incorporation date?
mipolate l.roa year, by(id) gen(l.roa.i) forward

[Carlo Lazzaro]

Huda:
I cannot test your code because I'm away from my desk at the moment.