 Orbell and Dawes are particularly concerned with an explanation for cooperative behavior that rests on the empirically supported hypothesis that individuals often base expectations about behavior of others on their knowledge of their own behavior and tendencies. This hypothesis suggests that a cooperator is more likely than a defector to expect others to cooperate and therefore, if he is rational, more likely to engage in the optional PD. Orbell and Dawes (1991) demonstrate that, if a cooperator is substantially more likely than a defector to expect his opponent to cooperate, then (provided the odds of his opponent cooperating are sufficiently high), a cooperator can actually expect a higher return than a defector in the optional PD. Orbell and Dawes (1993) present experimental evidence that participants in an optional PD do receive higher average payouts than those in the corresponding PD lacking the \(\bN\) move. They provide clever statistical arguments to support the following hypotheses: intending cooperators (those who cooperate when they must engage) do better in the optional PD than in the corresponding PD; intending defectors generally do worse in the optional PD; under some conditions these gains and losses are sufficient to make the intending cooperators better off than the intending defectors (as might be predicted by the theoretical result of the previous paper); and, finally, those who expect cooperation from others (as evidenced by their engagement) do so on the basis of their own tendency to cooperate rather rather than any direct discernment of the character of their opponent. (See  Transparency  below.)