Part I

The study of the occurrence of multiple sclerosis (MS) over time and in many places throughout the world has yielded several interesting clues that have been formulated into hypotheses concerning the causation of this illness. The strategies for carrying out occurrence research and etiologic(causal) research share many common requirements, but do differ. The former emphasize complete and accurate case ascertainment. For studies in which the main goal is assessment of possible risk factors for the development of MS, accurate case ascertainment is also crucial, but several other aspects not relevant to descriptive studies need to be considered. The two main ones are the measurement and collection …