cutepipico

Survivor Bias (survivorship bias) 生存者誤差

今天看blog看到這個詞，朋友問我Survivor Bias到底是什麼玩意
wiki解釋的非常專業,摘錄一段wiki的解釋

In finance, Survivorship bias is the tendency for failed companies to be excluded from performance studies because they no longer exist. It often causes the results of studies to skew higher because only companies which were successful enough to survive until the end of the period are included.

For example, a mutual fund company's selection of funds today will include only those that have been successful in the past. Many losing funds are closed and merged into other funds to hide poor performance. This is how 90% of extant funds can truthfully claim to have performance in the first quartile of their peers: the other three quarters of funds have closed.

In 1996 Elton, Gruber, & Blake showed that survivorship bias is larger in the small-fund sector than in large mutual funds (presumably because small funds have a high probability of folding). They estimate the size of the bias across the U.S. mutual fund industry as 0.9% per annum, where the bias is defined and measured as:

"Bias is defined as average α for surviving funds minus average α for all funds"

(Where α is the risk-adjusted return over the S&P 500. This is the standard measure of mutual fund out-performance).

很多財經網站解釋的非常專業不需要我多說
Survivor Bias 翻譯的生活化、日常化一點就是 :
當你看到一堆股票致富，你也準備辭掉工作靠炒股過活，你忽略掉有80%的股民已經輸掉退場。

當你看到巷口賣蛋捲的賺到翻，打算辭掉工作也來賣手工蛋捲，你忽略掉之前蛋塔店也是熱一時倒一堆。

眼前看到的都是成功的倖存者，檯面下有更多失敗的罹難者你看不見。