在股市的參與者當中，某些投資人必須長期持有股票部位，例如政府為民眾代操的四大基金、以及投信公司的股票型基金經理人。筆者推測這些大型投資者基於長期投資下，應選擇股價便宜時進場，而融資維持率接近追繳維持率時正是大盤的低點，符合長期投資者進場的時機，加以其手中部位的盈虧代表其操作績效，應更加願意在融資維持率低落時進場買入股票，因為此動作能夠產生類似護盤的效果，使融資維持率不致長時間跌破追繳維持率水準，引發大規模崩盤，進而使其手中部位產生虧損。
根據以上推測，筆者觀察股市中融資維持率以及股價指數的走勢，進而設計出稱為〝改良式濾嘴法則〞的交易策略，其中以月資料回測後發現報酬率顯著，但是以週資料及月資料進行回測後卻發現報酬率低落的現象，因此交易策略的結果顯示僅以融資維持率的高低區間做為交易策略的進出場指標似非可行的方法。

Some participants in stock market have to hold their position for longer time. For example, four major fund that government manage for people, and stock fund managed by investing trust company fund manager. Author suggest that “big investors” in stock market have to take care of their performance so that can keep their job. Under these pressure, “big investor” would willing to buy stocks when stock market crush, and this action will have similar results as “stock index protection effect” to avoid margin ratio fall down to margin call level for too long time , because , since it happened, stock market will fall to the lower level, and probably cause the stock market crush.
According to the assumption above, author observe relation between margin ratio and stock market index trend and develop a series of trading rule. But after counting in transaction fee, only month data has significant return , so author thought that use only one bench mark range to build trading rule is not effective.

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