1994issue C091-6
Constructing relative strength index lookbacks, bands, and confirmation filters
The relative strength index is a self-comparison oscillator built from one instrument’s own closing-price changes. Lookback, extreme bands, oscillator smoothing, and the confirmation rule are construction choices that can precede a trend change or mark an ending too early.
- The relative strength index compares an instrument only with its own past closes through an RS ratio of lookback-average up-close and down-close changes, then maps that ratio onto a scale between 1 and 100.
- Lookback is the free parameter: a shorter window can precede a trend change, while a window that is too short in a persistent trend can mark an ending too early.
- Extreme bands, oscillator smoothing, a midline cross, and a failure-swing rule are separate construction choices, not a single default reading.
- Support, resistance, and unconfirmed price extremes can appear on the oscillator before they are obvious on price, which is why the filter is treated as one tool among several.
A self-comparison, not a ranking
The relative strength index is built from one series of closing-price changes. The RS ratio is the lookback average of up-close changes divided by the lookback average of down-close changes. That ratio is mapped by 100 minus 100 divided by one plus the RS ratio.
The construction compares an instrument only with its own past closes. It does not rank that instrument against another instrument or a market index.
Lookback as the free parameter
The oscillator is scaled into a band between 1 and 100, so lookback is the free parameter that remains. A chosen lookback can make the reading precede a trend change. If the lookback is too short in a persistent trend, the same construction can mark an ending too early.
A 14-period lookback is the original and most common default. Nine-period and 25-period windows are also used. Longer windows reduce false alerts at the cost of more lag around peaks and troughs.
Extreme bands and regime substitutes
Standard extreme-band construction treats a move above 70 as proximity to an upside extreme or a reaction against an uptrend. A move below 30 is treated as proximity to a downside extreme. The same bands are used on both daily and weekly sampling.
In trending regimes, some constructions treat 60 as a ceiling on downtrend rallies and 40 as a floor on uptrend pullbacks. One illustrated downtrend reached 60 and then printed new price lows.
Smoothing and the midline cross
One construction variant applies oscillator smoothing with a nine-period simple moving average so turns in the indicator series are easier to mark.
Another construction uses a midline cross of 50 as the threshold, with a 21-week average suggested when the input is an index series.
Structure and the failure-swing rule
Support, resistance, and breakouts can be marked on the oscillator plot and may appear before the same structure is obvious on price. A failure-swing construction requires a second price extreme the oscillator does not confirm, then an oscillator close through the intervening peak.
Illustrated cases show a smoothed oscillator near 80 ahead of a downturn, a reading under 20 coinciding with price stabilization, and a multi-month divergence between the oscillator and price before a sustained advance. The filter is treated as one tool among several rather than a standalone reading.
All readings on this track · 26 readings
- 1991Constructing the relative strength index from seed and recursive averages
- 1991Inverting relative-strength-index closes for same-session rules
- 1991Seeded averages and the recursive-update
- 1993Restating relative-strength-index parameters after a smoothing change
- 1993Relative momentum construction by stretching the relative strength lookback
- 1994Constructing relative strength index lookbacks, bands, and confirmation filters
- 1994Building the relative-strength-index from signed close changes
- 1997Constructing the relative strength index as a bounded up-down close oscillator
- 2002Four-line oscillator construction for rule-based entries
- 2004Assembling a bounded RSI path
- 2004Constructing RSI on highs, lows, and reverse targets
- 2004Reverse-engineered RSI as an explicit next-bar price target
- 2006Self-adjusting RSI thresholds from the oscillator's own spread
- 2006Constructing adaptive overbought and oversold levels for a relative strength index
- 2006Relative Strength Index 50-line entry beyond the 70 and 30 extremes
- 2007Lock a followable rule set before testing RSI exits
- 2008RSI bands as a one-day shift of reverse-engineered levels
- 2008Constructing an asymmetrical RSI from adaptive up and down averages
- 2010Building a bounded oscillator from a rainbow smoother, relative strength, and inverse Fisher
- 2011Two-horizon weekly RSI with moving averages and stops
- 2011Percent-offset simple moving average bands with relative-strength confirmation
- 2011Fast and slow relative strength index as one mechanical rule book
- 2011Price-zone oscillator construction from signed closes
- 2015Constructing a zero-lag oscillator against a relative strength index baseline
- 2015Relative Strength Index as a baseline in 2015 software listings
- 2018Building a Fisherized deviation-scaled oscillator