I am working on a price elasticity problem and i am using Log-Log linear model. Below are the set of variables
Dependent variable: logarithm of my quantity sold (LogQ)
Independent variable: logarithm of my price(LogMyP), logarithm of price of my competitor price(for cross-price elasticity)(LogCoP), logarithm of my social media rating(LogMyR), logarithm of my competitors social media rating(LogCoR), logarithm of my unsold stock(LogMyS), logarithm of remaining shelf life of my product(LogMyShl), logarithm of market supply in percentage(LogMktspl), day of the week (6 dummy variables)
I need help in identifying set of endogenous and instrumental variables so that i can specify that in Instrumental Variable regression. I believe only logarithm of my price and logarithm of my competitor price are for the rest i do believe that it impacts my demand. The problem i am facing is how to decide which of the independent variable is exogenous or instrumental variable. Is there any test available or any procedure to identify if a variable is instrumental variable or is this purely a subjective thing? in any case can anyone help me identify the instrumental variables?