We employ a new approach for classifying methods of personality measurement such as self-judgment, mental ability, and lifespace measures and the data they produce. We divide these measures into two fundamental groups: personal-source data, which arise from the target person's own reports, and external-source data, which derive from the areas surrounding the person. These two broad classes are then further divided according to what they target and the response processes that produce them. We use the model to organize roughly a dozen kinds of data currently employed in the field. With this classification system in hand, we describe how much we might expect two types of measures of the same attribute to converge-and explain why methods often yield somewhat different results. Given that each measurement method has its own strengths and weaknesses, we examine the pros and cons of selecting a given type of measure to assess a specific area of personality.
