I have been learning from Statalist for some years now. Thank you for being there for us! First time I ask a question as I normally find solutions from reading other posts.

I have a wide dataset (40 observations) and an unbalanced panel (40 countries x 17 years observations)

My dependent variables (EMP1) are employment shares multiplied by 100
My main regressor (tech) is tech imports per million USD of total intermediates

Using my WIDE DATASET, I estimated long-differences using a set of controls (C1... C6) in years t-1 as all of them can be outcomes of the main regressor
So, I run regressions of the form:

Code:
 reg EMP1 tech(t1,t+15) C11995 C21995 C31995 C41995 [aweight=W1995], r
Then, I run regressions of the form

Code:
 ivreg EMP1 C11995 C21995 C31995 C41995 (tech=Z) [aweight=W1995], r
EMP1 = EMPt+15 - EMPt
tech = sum of tech from t up to t+15
using weight in year t-1 (W1995)

I am struggling to run first-difference regressions and fixed-effects regressions with the same variables in the panel dataset
I have data for my DV and controls from 1995 to 2011, and for my main regressor from 1996 to 2011
I do not manage to tell Stata to use the set of controls and the weight in the baseline year 1995

My panel dataset has the following variables, with observations for 40 countries and 17 years

Code:
              storage   display    value
variable name   type    format     label      variable label
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
country         str30   %30s                  Country name
year            int     %10.0g                
tech            float   %9.0g                 tech imports per million USD of total intermediates
AE              float   %9.0g                 Advanced Economy
EE              float   %9.0g                 Emerging Economy
C1              float   %9.0g                 offshoring share imported/total intermediates
C2              double  %10.0g                Exported intermediates in thousand USD
C3              float   %9.0g                 Output per capita in millions 2011 USD
C4              float   %9.0g                 Mean of population with full college
C5              float   %9.0g                 population 55-79 over population 20-54
C6              double  %10.0g                dependency ratio
W               double  %10.0g                Manufacturing value added
EMP1            float   %9.0g                 100 * shareKI/sharenFAB workers
EMP2            float   %9.0g                 100 * shareKI workers
EMP3            float   %9.0g                 100 * sharenFAB workers
EMP4            float   %9.0g                 share MGT workers
EMP5            float   %9.0g                 share RD workers
EMP6            float   %9.0g                 100 * shareKI/sharebFAB workers
EMP7            float   %9.0g                 100 * sharebFAB workers
country_id      float   %14.0g     country_id
                                              group(country)
I want to compare the estimates from using fixed-effects and first-difference estimators.
Additionally, I want to see the changing effect of tech on the EMP1, for which I want to run first-difference regressions using 5 year intervals
Array


I have checked xtreg and areg, but I do not know how to tell Stata to use my controls (C1...C6) and the weight W using year 1995 values, then I was suggested to use areg.
I would be grateful for any help as I am stuck here.
David