4. (a) Owens uses a 2001 law change (erasing the juvenile delinquency records of 23-25 year olds sentenced to prison) to estimate the incapacitation effect of longer prison terms. Now suppose that, a few years before 2001, psychological counseling for juvenile delinquents became mandatory and that, by 2001, this reduced the ex delinguents' propensity to commit crime as adults. In this case, will Owens' method still give unbiased estimates of the effect of longer prison terms on crime? Explain. (15) (b)1n Donohue and Levitt's paper on abortion and crime, the authors nd that crime peaked in 1991 and fell afterwards. If the abortion law theory is correct, how long do you expect the legalization of abortion to have an effect on crime rates? Why