What it means
A moving average is the average price of a security over a set number of recent periods, such as 10 or 50 days, and it smooths out day-to-day noise. The disparity index compares the current price with that average and shows the gap as a percentage of the average.
The bigger the gap, the more the price has run away from its recent trend. Traders read the indicator in two main ways.
A very high positive reading suggests the price has risen faster than usual and may be due for a pause or pullback, while a very negative reading suggests it has fallen sharply and may be due to recover. A move from negative to positive, crossing the zero line, can be read as a shift in momentum.
The right levels for what counts as extreme depend on the security and the time frame. A volatile stock may regularly show readings of 10% or more without any problem, while a steady large company may rarely exceed 3%.
Analysts usually look at the past behaviour of the same security to decide what is unusual. For finance teams and non-specialists, the indicator is best seen as one input rather than a rule.
It does not know about earnings, news or the wider economy, and a strongly trending market can stay extended for a long time. Treasury teams that follow commodity or currency prices sometimes use it as a quick check on whether a purchase is being made after a sharp rise.
A nuance is that the result depends on the length of the moving average chosen. A short average reacts quickly and produces many signals, while a long one reacts slowly and gives fewer but steadier ones.
Choosing a period that matches the planned holding time helps avoid confusion.
In practice
Real-world examples.
Example
A trader notes that a technology stock has a disparity index of 12% against its 20-day average, far above its usual range of 3%. She reduces her position, expecting the rally to slow. The price drifts sideways over the next week.
Example
A procurement manager follows the price of copper. The metal is 9% above its 50-day average, so she delays a large purchase until the gap narrows. She buys two weeks later at a lower price.
Example
A portfolio analyst screens a list of 500 stocks for readings below minus 10%. She uses the list as a starting point for further research into companies that may have been oversold. After checking their reports, she keeps only those with sound finances.
Formula
Calculation
Disparity index = (latest closing price - moving average) / moving average x 100
A stock closes at $54.00 and its 20-day moving average is $50.00. Disparity index = ($54.00 - $50.00) / $50.00 x 100 = 4 / 50 x 100 = 8%. If the stock later closes at $47.50 with the average at $50.00, the index is ($47.50 - $50.00) / $50.00 x 100 = -5%, showing the price is 5% below its recent average.Case study
Seen in the real world.
Northgate Metals is an illustrative, fictional manufacturer that buys aluminium each month and keeps a simple price chart. Its purchasing manager added a 30-day disparity index to the chart to help time larger purchases.
In one month, aluminium rose to $2,600 per tonne against a 30-day average of $2,400, a disparity index of ($2,600 - $2,400) / $2,400 x 100 = 8.3%. The manager held back half the usual order of 500 tonnes and bought the remaining 250 tonnes when the price dropped to $2,450.
The saving on the delayed half was ($2,600 - $2,450) x 250 = $37,500. The price might equally have kept rising, and the company recognised that the tool guides timing rather than predicting prices. The illustrative lesson is that a simple indicator can support a buying plan if it is used with care.
Watch out
Common mistakes.
- Treating a high reading as a guaranteed sell signal, when a strong trend can keep a price stretched for a long time.
- Using the same threshold for every security, when volatile assets produce larger readings than stable ones.
- Ignoring the moving average period, when a short period and a long period can give opposite readings for the same price.
Questions
People also ask.
What does a disparity index of zero mean?
It means the latest price is exactly equal to the moving average.
Is the disparity index the same as a percentage price oscillator?
No. The disparity index compares price with one average, while the percentage price oscillator compares two averages with each other.
Can the index be used on any asset?
Yes, on any asset with a regular price series, such as shares, currencies and commodities, though the thresholds must be adapted to each.
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