Many of the fundamental data required for the study of history, sociology, politics, or economics in Africa are stored up in the memories of a few elders, chiefs, priests, palace and town historians, and in the general knowledge of the average man and woman. To make such data available, the techniques of questionnaires and interviews are increasingly being employed to tap these unwritten sources. But great care needs to be taken in preparing the questions, studying the problems likely to arise where they are used, and in assessing the results. The care necessary on these matters has been well indicated by Girard: