apparatus for relating pain and activity experienced by a patient comprises : pain transducing means for allowing a patient to select any one pain level from a predetermined number of pain levels and for producing a pain level signal indicative of the selected level ; activity transducing means responsive to the pain level signal for measuring a level of a parameter of a physical activity of the patient near the time corresponding to the selection of the pain level and for producing an activity parameter level signal indicative of the measured level of the parameter ; and relating means responsive to the pain level signal and the activity parameter level signal for characterizing the activity of the patient corresponding to the selected level of pain to be one activity level of a predetermined number of predefined activity levels and for producing a signal indicative of the characterized level of activity and the corresponding pain level .