A method for assessing volunteer bias and its application to a cardiovascular disease prevention progamme involving physical activity.

Studies of chronic disease may require long-term observation of volunteer participants. This is a characteristic of investigations of primary or secondary prevention of cardiovascular disease by increased level of physical activity. Activation of sedentary, middle-aged, high risk men requires a substantial personal commitment on their part to a long-term programme. Because of self-selection, individuals who volunteer for such programmes cannot be assumed to be representative of the populations from which they come. To the best of our knowledge, there has been no systematic investigation of such self-selection based upon a study designed for that purpose. We found little consistent tendency for vouunteering behaviour to be associated with serum cholesterol, blood pressure, relative weight, level of activity at work, or Type A hehaviour variables.