Which of the 8 possible variables (factors) affect the internal validity of the conclusions concern you the most as it relates to this article? Explain and justify your response

Q3 Which of the 8 possible variables (factors) listed on page 68 of your textbook that affect the internal validity of the conclusions concern you the most as it relates to this research article? Explain and justify your response.Book is Hagan, F. E. (2010). Research methods in criminal justice and criminology (8th ed.). Upper Saddle River, NJ: Prentice Hall.Article is Kempinen, C. A., & Kurlychek, M. C. (2003). An Outcome Evaluation of Pennsylvania’s Boot Camp: Does Rehabilitative Programming Within a Disciplinary Setting Reduce Recidivism?. CRIME & DELINQUENCY, 49(4), 581-602.