>ok, dd, so how do they conceive of people then? methodological
>individualism or not?
Methodological individualism doesn't foreclose collective action or irrationality. Keynes' finance-as-beauty-contest predicts that individuals playing the market for themselves will act as if in concert with others (i.e. herd behavior). And they will not be beholden to "fundamentals." Behavioral finance predicts that "noise" traders (i.e. unsophisticated non-professionals) work against the rationality of markets in consistent ways, rather than at random.
That's different than acting deliberately as a collective unit (i.e. having a meeting, etc.), though if others' moves are taken for granted in your own, then the effect can be similar--ie. Malaysian authorities buying up gov't securities to prevent short selling a few years back (if I remember right).
Christian