Clear exposition and nascent use of clear graphics
Prior to becoming THE authority on the graphic display of quantitative information, Edward Tufte was a political scientist of the first order, an excellent statistician and a teacher par excellence. This slim volume is one of the clearest introduction to the use of regression analysis one could hope to find. I used it extensively in graduate school and have consulted frequently since. The clear use of graphics foretell Tufte's groundbreaking later work and provide a guide for thinking statistically.
More importantly, Tufte is rigorous and demands one to constantly evaluate the quality of the data at hand and the logical or causal relationships one is positing. \
A great book for the beginning data analyst and a must for political science graduate students.
