在生物多樣性的研究領域裡，bata多樣性指標主要是用來衡量兩個以上不同群落之間生物的相異度，我們可以利用不同群落之間的共同種(shared species)和特有種(endemic species)定義一些指標來做為量度的標準。在文獻中有許多量度的指標被提出，包括Jaccard出現指標及豐富指標、Sørensen出現指標及豐富指標、Lennon出現指標及豐富指標、Morisita指標以及Bray-Curtis相似性指標等等。
本文主要針對Bray-Curtis相似性指標進行討論，內容可以分為三部分，第一部分就Bray-Curtis指標的定義及原始估計量來做探討，以其一階期望值來推測原始估計量對真實指標值的估計情形，再經由模擬此估計量對真實指標值的估計情形，是否如其一階期望值所預期的結果。第二部分針對Bray-Curtis原始估計量會受到抽樣比例所影響，以模擬方式比較其他相似性估計量是不是也有相同的表現。最後則是以模擬方式探討在各種不同的假設條件下，群落中物種的相對豐富度所服從的結構，對於估計量的表現情形之影響。

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