Key points are not available for this paper at this time.
Alan E. Gross, Barbara S. Wallston, Irving M. Piliavin, Beneficiary Attractiveness and Cost as Determinants of Responses to Routine Requests for Help, Sociometry, Vol. 38, No. 1 (Mar., 1975), pp. 131-140
Gross et al. (Sat,) studied this question.