For a regression of test score (T) on the endogenous variablestudent-teacher ratio (R), Hoxby (2000) suggests using as aninstrument the deviation of potential enrollment from its long-termtrend (P), where \"potential enrollment\" means how many children ofkindergarten age there are (whether or not they attend publicschool). Which of the following arguments would NOT support P as aninstrument for R?
| a. | Due to high adjustment costs of buildings and teachers and thesmall/discrete number of classrooms per school, schools cannotperfectly adjust each year to maintain a target student-teacherratio |
| b. | Parents with young children are more likely to move into goodschool districts with low student-teacher ratio |
| c. | There are fluctuations in birth rate due to sheer randomchance |
| d. | Changes in school district quality are slow and contribute tothe long-term enrollment trend, but not deviations from thetrend |
PLEASE PROVIDE EXPLANATION IN ANSWER
