Which of the following is not a source of data collection.

"Classification" is not a source of data collection. Observation involves the gathering of data by observing a phenomenon or behavior, while interviews involve asking questions to individuals or groups to collect information. Questionnaires involve the use of written or printed questions to collect data from individuals, while classification is the process of arranging objects, people, or data into categories based on their common characteristics. Therefore, classification is not a source of data collection but rather a technique used to organize collected data.