What is the primary threat to internal validity that could confound the results of a regression discontinuity study?

Two constitutionally mandated mechanisms for checking the prime minister are

a. the impeachment process and variable elections. b. the vote of no confidence and the convention of collective responsibility. c. the monarch and the House of Lords. d. question time and the election process. e. fusion of powers and judicial review.

“Dictators are more likely to provide public goods for their citizens than democratic leaders are.” Is this a scientific statement?

A. Yes B. No