Lena smiled. "That’s the guide to design and analysis. No randomization? No problem. Just more thinking." Quasi-experimentation isn’t “second-best.” It’s a toolkit for causal inference when experiments are impossible. Master the threats (history, selection, maturation, regression), choose a design (ITS, DID, nonequivalent groups), and analyze with care — robust standard errors and pre-trend checks are your friends.
"Lena, look," Hartley said, tapping his desk. "I installed it in Ms. Chen’s third-grade class. She’s our best teacher. The other third-grade class, Mr. Abel’s, is using the old curriculum. After three months, I’ll compare their test scores. Simple, right?" quasi-experimentation a guide to design and analysis pdf
Result: The +7 points was statistically significant (p < .01) and practically meaningful. Lena presented to Hartley: "The software works, but only by 7 points, not the 15-point jump you saw in the raw comparison. The raw difference was inflated by Ms. Chen’s prior excellence." Lena smiled