Hart proved the difficulty of deriving general comparative statics in portfolio weights. Instead, we derive new comparative statics for the distribution of payoffs: A is less risk averse than B iff A's payoff is always distributed as B's payoff plus a non-negative random variable plus...

We propose a tractable equilibrium model to examine how margin requirements affectasset prices, market volatility, and market participants' welfare. Weshow that margin requirements can have opposite effects on market volatility whenthey constrain different investors and thus can help explain why...