Question 4: (10 marks) We wish to use a DDD model to evaluate the impact of a policy change (for improving labour income y) in region A (but not region B) in period 1 (but not period 0) for low income group L (but not high income group H). We have the labour income data for all regions (A and B), all time periods (0 and 1), and for all income groups (L and H). Please establish the DDD model for labour income y so that you can effectively evaluate the impact of the policy change on labour income y. Please explain which parameter(s) can be used to evaluate the impact of the policy change and how to interpret the parameter(s). Question 4: (10 marks) We wish to use a DDD model to evaluate the impact of a policy change (for improving labour income y) in region A (but not region B) in period 1 (but not period 0) for low income group L (but not high income group H). We have the labour income data for all regions (A and B), all time periods (0 and 1), and for all income groups (L and H). Please establish the DDD model for labour income y so that you can effectively evaluate the impact of the policy change on labour income y. Please explain which parameter(s) can be used to evaluate the impact of the policy change and how to interpret the parameter(s)