Gaya APA

Shadish, W, R. et al (2002). Experimental and Quasi - Experimental Designs : for Generalized Causal Inference . USA: Wadsworth Cengage Learning.

Gaya MLA

Shadish, William, R.. et al. "Experimental and Quasi - Experimental Designs : for Generalized Causal Inference". USA: Wadsworth Cengage Learning, 2002. Text.