正成交量指標（PVI）

正成交量指標由Norman Fosback在他 的《股市邏輯》一書中引進。它通常會結合負成交量指標使用，用來確認市場趨勢。正成交量指標是建立在市場活躍期是受大衆主導的假設之上的，而負成交量指標則假設市場波動小的時候則受內部人士支配。正成交量指標突出顯示那些成交量較前一日高的天數，而負成交量則突出成交量下降的天數。

交易信號
Fosback 認為，如果正成交量指標位於年移動平均線下方，那麼市場將有67%的可能性處於熊市階段；當正成交量指標位於年移動均線上方時，市場處於熊市的概率下降到21%。
• 正成交量指標向下穿過年移動平均線是對熊市市場即將到來的確認信號。

示例
寶潔公司股票以及  正成交量指標、   9日EMA (快線) 、  255日EMA（慢線）。

 
1. MA快線向下穿過慢線MA，是熊市信號 [-] 。
2. 快線MA向上穿過慢線MA，熊市的終結 [+]。
MA平滑線（快線MA）避免了正成交量指標發出的錯誤信號。

設定
指數移動平均數（EMA）的預設設定為255日。

公式
1. 找出昨日的PVI
2. 如果今日的成交量大於昨日，則今日的PVI值為昨日PVI加上：
           { ( 今日收盤價 – 昨日收盤價 ) / 昨日收盤價 } * 昨日PVI
3. 否則，今日的PVI值與昨日一致。

Positive Volume Index
The Positive Volume Index was introduced (in Stock Market Logic) by Norman Fosback and is often used in conjunction with Negative Volume Index to identify bull and bear markets.
Positive Volume Index is based on the assumption that the uninformed crowd dominates trading on active days.Negative Volume Index assumes that the smart money dominates trading on quiet days.
Positive Volume Index highlights days when volume is up on the previous day. Negative Volume Index highlights days when volume is down.
Trading Signals
Fosback maintains that there is a 67% probability of a bear market when Positive Volume Index is below its 1 year moving average. The probability drops to 21% when PVI is above the moving average.
• Positive Volume Index crossing to below its one year moving average confirms the approach of a bear market.
EXAMPLE
Procter & Gamble with   Positive Volume Index   9-day exponential moving average (fast MA) and   255-day exponential moving average (slow MA).
1. Fast MA crosses to below the slow MA. Bear signal [-].
2. Fast MA crosses back to above the slow MA. End of bear signal [+].
Indicator smoothing (the fast MA) eliminates several whipsaws from the Positive Volume Index.
Setup
The default setting for the exponential moving average is 255 days. To alter the default settings - Edit Indicator Settings.
See Indicator Panel for directions on how to set up indicators.
Formula
1. Take yesterday's Positive Volume Index
2. If today's volume is greater than yesterday, add:
           { ( Close [today] - Close [yesterday] ) / Close [yesterday] } * PVI [yesterday]
3. Otherwise, add zero.

文章翻譯由兄弟財經提供

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