负成交量指标(NVI)

负成交量指标在Norman Fosback的《股市逻辑》一书中有所介绍。它通常会与正成交量指标结合起来鉴别市场是否处于牛市。这两种指标假设，没有数据的时候市场是受“内部人士”主导，市场波动剧烈的时候则被大众主导。NVI是基于下降的交易量计算得出的。而正成交量指标则是根据第二日的交易量大于前一日得出。

交易信号
Fosback 认为，如果NVI位于其1年MA的上方，那么市场就有95%的几率处于牛市。当NVI位于下方时，牛市概率就下降到50%。
• NVI向上穿过它的一年MA可以更加确定牛市的到来。
可以利用平滑指标过滤掉小趋势。

示例：
沃尔玛公司股价以及  NVI、   9日EMA以及    NVI的255 EMA。

 
9日的EMA向上穿过255日MA表面牛市的开始：NVI本身波动太频繁。
1. 9日EMA向上穿过255日MA，趋势开始上升 [+] 。
2. 在第二个[+]出现之前，趋势很好的处于上升态势。
3. 上升趋势中价格出现回调。[?] 表示趋势的不确定。
4. 9日快线MA向上穿过慢线MA [+] ，但是接下来的上升趋势不强劲。
5. 另外一个上升趋势信号[+]，但是趋势更加微弱。

设置
默认NVI的EMA设置是255日。

公式
1. 找出昨日的NVI。
2. 如果今日的交易量小于昨日的，在昨日的基础上增加：
           { ( 今日的收盘价 – 昨日的收盘价 ) / 昨日的收盘价 } * 昨日NVI
3. 否则，增加0

Negative Volume Index
The Negative Volume Index was introduced (in Stock Market Logic) by Norman Fosback and is often used in conjunction with Positive Volume Index to identify bull markets. The two indicators are based on the assumption that the smart money dominates trading on quiet days and that the uninformed crowd dominates trading on active days.
Negative Volume Index is based on days when volume is down from the previous day. Positive Volume Index is based on days when volume is up on the previous day.
Trading Signals
Fosback maintains that there is a 95% probability of a bull market when Negative Volume Index is above its 1 year moving average. The probability drops to 50% when NVI is below the moving average.
• Negative Volume Index crossing to above its one year moving average confirms the approach of a bull market.
Use Indicator Smoothing to eliminate whipsaws.
 
EXAMPLE
Wal-Mart Stores Inc. plotted with   Negative Volume Index,   9-day exponential moving average and   255 day exponential moving average (of NVI).
Use the 9-day moving average crossing the 255-day MA to signal the start of a bull-trend: The Negative Volume Index itself has too many whipsaws.
1. The 9-day moving average crosses to above the 255-day MA, indicating an up-trend [+].
2. The trend is well on its way before the next signal [+].
3. A whipsaw occurs during a strong down-trend. The signal [?] is incorrect.
4. The fast MA crosses to above the slow MA [+] but the ensuing trend is not very strong.
5. Another signal [+] but the rally is even weaker.
Setup
See Indicator Panel for directions on how to set up an indicator.
The default setting for the Negative Volume Index (exponential moving average) is 255 days. To alter the default settings - Edit Indicator Settings.
Formula
1. Take yesterday's Negative Volume Index
2. If today's volume is lower than yesterday, add:
           { ( Close [today] - Close [yesterday] ) / Close [yesterday] } * NVI [yesterday]
3. Otherwise, add zero.

文章翻译由兄弟财经提供

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