Collection of data constitutes the first step in a statistical investigation. Utmost care must be exercised in collecting data because they form the foundation of statistical analysis. If data are faulty, the conclusions drawn can never be reliable. The data may be available from existing published or unpublished sources or else may be collected by the investigator himself. The firsthand collection of data is one of the most difficult and important tasks faced by a statistician. Therefore, like all scientific pursuits, the investigator must take into account whatever data have already been collected by others. This would save the investigator from foreseeable pitfalls, unnecessary labour and duplication of efforts.