The Asymmetric Relation Between Initial Margin Requirements and Stock Market Volatility Across Bull and Bear Markets
研究发现，正常和牛市期间较高的初始保证金要求会降低后续股市波动，但熊市期间无此关系；保证金提高会降低股票收益条件均值，建议在下跌市场中降低保证金以增强流动性，随后提高以防止杠杆效应。
Higher initial margin requirements are associated with lower subsequent stock market volatility during normal and bull periods, but show no relationship during bear periods. Higher margins are also negatively related to the conditional mean of stock returns, apparently because they reduce systemic risk. We conclude that a prudential rule for setting margins (or other regulatory restrictions) is to lower them in sharply declining markets in order to enhance liquidity and avoid a depyramiding effect in stock prices, but subsequently raise them and keep them at the higher level in order to prevent a future pyramiding effect