Donor attitudes, intentions, and behaviors have typically been conceptualized as organized along a bipolar continuum. This conceptualization is evident in I. G. Sarason et al.'s study of increasing participation in a bone-marrow registry in this issue. When the cumulative research on blood, bone-marrow, and organ donor behavior is considered, however, evidence suggests that a single, bipolar continuum may be insufficient and that a 2-dimensional (Positivity x Negativity) evaluative space may be minimally required to effectively represent and target the underlying substrates of donor behaviors. Negative beliefs and fears may constitute a particularly difficult obstacle to inducing donor behaviors and, thus, to promoting self-perceptions by people as donors. Understanding and changing these negative substrates, therefore, may be important if public health campaigns to increase donor behavior are to be cost-effective.
