I'm guessing that you want to disaggregate GDP data from quarterly frequency to monthly frequency? Industrial production index is an ideal indicator since it is highly correlated with GDP and available on a monthly basis. Absence of industrial production index, other good indicator candidates that are also available on a monthly basis will be any of the labor market indicators such as total employment, employment ratio, unemployment rate, etc.

Prof @Francis W Ahking, Thanks a lot..please, any reference for the LA our market indicators as an indicator variable in disaggregating GDP.

You can do nowcasting of GDP using monthly indicators of economic activities, Besides industrial production and unemployment as suggested in the previous reply, you can use many other variables like total credit growth, consumer price index, imports and exports...etc. These variables are collectively used in a nowcasting model to approximately estimate GDP at a monthly frequency, you can find more details in studies of GDP nowcasting.

You probably know that methods of disagregating quarterly data into monthly allow you to use only one indicator, and it is extremely difficult to accurately approximate monthly GDP using one indicator, especially in your case where industrial production data are not available. Therefore it is more advisable to use the nowcasting model to obtain more accurate approximations of monthly GDP. These models can be easily estimated using R or Matlab if you are familiar with these statical programming languages.

Thanks so much @Boubeker Med, can you suggest good articles that uses nowcasting for disaggregation of data from quarterly to monthly.

Hamid Muili

The empirical macro toolbox from Matlab provides a very straightforward method to construct Monthly GDP based on monthly time series of several economic variables, detailed guidance on this method is provided in the user guide of the toolbox (section 3.7.1)

Technical Report A hitchhiker guide to empirical macro models *

Also, there is the "nowcasting" package in R, but I'm not sure whether this package can nowcast the entire period or only months of the current quarter

However, your main problem is the lack of monthly industrial production data which is very essential to use the nowcasting model. That said, your problem may be solvable by using monthly electricity usage or energy consumption to compensate for monthly data of industrial production. For more details check the article linked below

https://www.eia.gov/workingpapers/pdf/electricity_indicator.pdf