共同基金投資法－單筆與定期定額比較

Abstract

本文採用蒙地卡羅模擬法分別比較台灣共同基金中的股票型以及平衡型在定期定額以及單筆投資法下，何者的報酬為佳。 我們採用Account Method 將模擬出數萬條的路徑下的報酬給予適當的權重，以求可以更全面性的探討各種不同的情境下所採用的投資策略不同所產生的報酬表現。結論發現若單就同一類型基金來看，單筆投資法在短期投資中較定期定額為佳，然而就長期而言，定期定額法報酬會逐漸超過單筆投資法，乃是藉由時間效果以及考慮了景氣波動下，定期定額投資人可攤低成本，提高其報酬率。同時發現平衡型基金的報酬變動沒有像股票型基金那麼劇烈；在考量風險後，會發現平衡型基金的報酬明顯優於股票型。 本文同時探討在放寬小額投資人的投資條件限制下（如定期定額投資人可以選擇停止扣款，或是小額投資人不論在定期定額以及單筆投資法下皆可以依當時投資報酬，自行訂定出場時機）投資人的報酬會如何改變，以求更貼近現實世界投資人行為模式下的報酬。結論發現放寬限制後，小額投資人在定期定額以及單筆投資法下其投資報酬皆明顯提升，同時又以定期定額策略下結合逢高的停止扣款機制、逢低不出場以及見好就收的出場機制下，其投資人的報酬最佳－乃是因為其嚴謹的投資策略才能確實享受到定期定額攤低成本的好處。

Through the Monte Carlo Simulation approach, we found that neither Lump Sum (LS) nor Dollar Cost Averaging (DCA) can be a dominant strategy for the diverse conditions we set to simulate the Taiwanese fund market, under the account method. Our research simulates the stock fund and the balanced fund, to observe the returns of LS and DCA strategies, and we found that most of the time, these two types of funds act similarly, although the balanced fund is less volatile than the stock fund, as reflected with its lower return (μ) and standard deviation parameters (σ). After considering risk, the balanced fund type brings higher rewards than the stock fund in most situations. However, if we consider investing returns only, the issue of adopting LS or DCA dominates over fund types. By setting different conditions and running different scenarios we can claim that DCA is a more conservative and long term strategy than LS, so that DCA yields better performance under longer investing periods and in a strong downturn, if the investor can tolerate the losses, as the DCA investor will benefit from the cost-averaging effect. By relaxing constraints in buying units and leaving the market, both LS and DCA can yield better annualized investing returns compared to the original scenarios, but the DCA investor tends to see a better yield if he continues to “keep the faith” and tolerates the losses so as to follow the more disciplined investing strategy in a down market.