正成交量指标（PVI）

正成交量指标由Norman Fosback在他 的《股市逻辑》一书中引进。它通常会结合负成交量指标使用，用来确认市场趋势。正成交量指标是建立在市场活跃期是受大众主导的假设之上的，而负成交量指标则假设市场波动小的时候则受内部人士支配。正成交量指标突出显示那些成交量较前一日高的天数，而负成交量则突出成交量下降的天数。

交易信号
Fosback 认为，如果正成交量指标位于年移动平均线下方，那么市场将有67%的可能性处于熊市阶段；当正成交量指标位于年移动均线上方时，市场处于熊市的概率下降到21%。
• 正成交量指标向下穿过年移动平均线是对熊市市场即将到来的确认信号。

示例
宝洁公司股票以及  正成交量指标、   9日EMA (快线) 、  255日EMA（慢线）。

 
1. MA快线向下穿过慢线MA，是熊市信号 [-] 。
2. 快线MA向上穿过慢线MA，熊市的终结 [+]。
MA平滑线（快线MA）避免了正成交量指标发出的错误信号。

设置
指数移动平均数（EMA）的默认设置为255日。

公式
1. 找出昨日的PVI
2. 如果今日的成交量大于昨日，则今日的PVI值为昨日PVI加上：
           { ( 今日收盘价 – 昨日收盘价 ) / 昨日收盘价 } * 昨日PVI
3. 否则，今日的PVI值与昨日一致。

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.

文章翻译由兄弟财经提供

本文来源：http://www.incrediblecharts.com/indicators/positive_volume_index.php