負成交量指標(NVI)

負成交量指標在Norman Fosback的《股市邏輯》一書中有所介紹。它通常會與正成交量指標結合起來鑒別市場是否處於牛市。這兩種指標假設，沒有數據的時候市場是受“內部人士”主導，市場波動劇烈的時候則被大衆主導。NVI是基於下降的交易量計算得出的。而正成交量指標則是根據第二日的交易量大於前一日得出。

交易信號
Fosback 認為，如果NVI位於其1年MA的上方，那麼市場就有95%的幾率處於牛市。當NVI位於下方時，牛市概率就下降到50%。
• NVI向上穿過它的一年MA可以更加確定牛市的到來。
可以利用平滑指標過濾掉小趨勢。

示例：
沃爾瑪公司股價以及  NVI、   9日EMA以及    NVI的255 EMA。

 
9日的EMA向上穿過255日MA表面牛市的開始：NVI本身波動太頻繁。
1. 9日EMA向上穿過255日MA，趨勢開始上升 [+] 。
2. 在第二個[+]出現之前，趨勢很好的處於上升態勢。
3. 上升趨勢中價格出現回調。[?] 表示趨勢的不確定。
4. 9日快線MA向上穿過慢線MA [+] ，但是接下來的上升趨勢不強勁。
5. 另外一個上升趨勢信號[+]，但是趨勢更加微弱。

設定
預設NVI的EMA設定是255日。

公式
1. 找出昨日的NVI。
2. 如果今日的交易量小於昨日的，在昨日的基础上增加：
           { ( 今日的收盤價 – 昨日的收盤價 ) / 昨日的收盤價 } * 昨日NVI
3. 否則，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.

文章翻譯由兄弟財經提供

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