 In a survey of the field several years after the publication of the results reported above, Axelrod and Dion, chronicle several successes of TFT and modifications of it. They conclude that “research has shown that many of Axelrod's findings…can be generalized to settings that are quite different from the original two-player iterated prisoner's dilemma game.” But in several reasonable settings TFT has serious drawbacks. One such case, noted in the Axelrod and Dion survey, is when attempts are made to incorporate the plausible assumption that players are subject to errors of execution and perception. There are a number of ways this can be done. Bendor, for example, considers “noisy payoffs.” When a player cooperates while its opponent defects, its payoff is \(S+e\), where \(e\) is a random variable whose expected value is \(0\). Each player infers the other's move from its own payoff, and so if \(e\) is sufficiently high its inference may be mistaken. Sugden (pp. 112–115) considers players who have a certain probability of making an error of execution that is apparent to them but not their opponents. Such players can adopt strategies by which they “atone” for mistaken defections by being more cooperative on later rounds than they would be after intended defection. Assuming that players themselves cannot distinguish a mistaken move or observation from a real one, however, the simplest way to model the inevitability of error is simply to forbid completely deterministic strategies like TFT, replacing them with “imperfect” counterparts, like “imitate the other player's last move with 99% probability and oppose it with 1% probability.” Imperfect TFT is much less attractive than its deterministic sibling, because when two imperfect TFT strategies play each other, an “error” by either one will set off a long chain of moves in which the players take turns defecting. In a long iterated game between two imperfect TFT's with any probability \(p\) of error, \(0 \lt p \lt \tfrac{1}{2}\), players will approach the same average payoffs as in a game between two strategies that choose randomly between cooperation and defection, namely \(\tfrac{1}{4}(R+P+S+T)\). That is considerably worse than the payoff of \(R\), that results when \(p=0\).