4. Suppose you are interested in the policy effect of a free drug addiction treatment for drug addicts in British Columbia, Canada. You recruited 500 drug addicts in BC and randomly divided them into two groups. For the first group (the treatment group), you provided them the new drug addiction treatment. For the rest (the control group), you just distrubuted pamphlets that explain how harmful drug addition is. You examined the difference of drug use at the end of your experiment. a) Explain whether this research design is internally vaild (define what is internal validity). b) Do you think the results from this research would be externally valid? (define external validity)