I have data from 214 countries that range from 1990 to 2014. My dependent variables (I'm doing more than one regression) are just primary/secondary net enrollment rates for both sexes/males/females, so six variables. My independent variables are 'energy consumption (kWh per capita),' 'ict goods imports (% of total imports),' 'internet users (per 100 people),' '% with access to improved sanitation facilities,' 'health expenditure per capita PPP,' 'GNI PPP,' '#ofteachers in whatever I'm regressing,' and 'age dependency ratio, young.'
I'm using a panel data fixed effects model. My question is this — do I keep all of these independent variables as is? I have one professor who has suggested that I change them into growth rates, but the data has empty spaces in between different years in the same country.