The paper describes a new, logic-based methodology for analyzing observatio
ns. The key features of the Logical Analysis of Data (LAD) are the discover
y of minimal sets of features necessary for explaining all observations and
the detection of hidden patterns in the data capable of distinguishing obs
ervations describing "positive" outcome events from "negative" outcome even
ts. Combinations of such patterns are used for developing general classific
ation procedures. An implementation of this methodology is described in the
paper along with the results of numerical experiments demonstrating the cl
assification performance of LAD in comparison with the reported results of
other procedures. In the final section, we describe three pilot studies on
applications of LAD to oil exploration, psychometric testing, and the analy
sis of developments in the Chinese transitional economy. These pilot studie
s demonstrate not only the classification power of LAD, but also its flexib
ility and capability to provide solutions to various case-dependent problem
s.