Instruct: Classify Amazon reviews into positive or negative sentiment
Query: a lasting contribution

I grant that it's not the most up-to-date, transparent, visually stimulating, or artfully written book. Even so, it's very rewarding for a reader who's serious about expanding his/her toolkit and gaining a more professional grasp of challenging issues in research design--experimental, non experimental, or quasi-experimental. Material on threats to validity, especially, continues to be cited extremely widely. Their discussion of time series modelling is intriguing, and they offer a particularly thought-provoking section on the intricacies of analyzing gain scores and the choice of ANOVA vs. ANCOVA.