Chapter 5 of 9
Momentum, RSI and indicator limitations
Understand rate of change, relative-strength calculations and why overbought does not automatically mean a price must fall.
In this chapter
Momentum measures change under a definition #
A simple rate of change compares the current observation with an earlier one: ROC = (current ÷ earlier − 1) × 100. The selected lookback changes the question. A positive short-window ROC can coexist with a negative longer-window ROC.
Momentum is a transformation of observed prices, not independent proof about future demand. A large past move can be followed by continuation, reversal or a range. The surrounding hypothesis and evidence must explain which outcome is being studied.
RSI compares smoothed gains and losses #
Under a common Wilder convention, RSI = 100 − 100 ÷ (1 + average gain ÷ average loss). Gains and losses are smoothed over a chosen window. Software conventions for initialization and zero-loss cases can affect displayed values.
A high RSI means recent upward changes dominate recent downward changes under that calculation. The label overbought is not a settlement rule and does not require prices to reverse. Strong trends can retain extreme readings for extended periods.
Avoid multiplying the same evidence #
RSI, ROC and moving-average indicators can respond to the same underlying price sequence. Three similar signals are not necessarily three independent confirmations. Divergence between an indicator and price is also a description requiring a consistent definition and a test.
Use adjusted, consistent data and identify when an observation is available. A strategy must survive costs and alternative samples before its historical behavior can be interpreted responsibly. An indicator does not replace assessment of loss, liquidity or option premium risk.
Decision lab: An oscillator does not promise mean reversion #
A bounded indicator can remain elevated through a persistent trend. “Overbought” is a label generated by a calculation, not proof of imminent decline. Reversing merely because the indicator reached a threshold embeds a market-regime hypothesis.
Define the threshold, signal timing, entry, invalidation and exit. Compare trend and range subsets without selecting the labels from future outcomes. Document the denominator and lookback used in the indicator; similar names can conceal different implementations.
Hypothetical worked example
Understand the ratio rather than the label
If average gain is 3 and average loss is 1 under the chosen smoothing convention, relative strength is 3 and RSI is 100 − 100 ÷ 4 = 75.
If positive observations continue, RSI can remain elevated. Taking an extreme reading as a guaranteed reversal could therefore be wrong even when the number was calculated correctly.
A move from 100 to 110 has a 10% ROC over that window. A move from 110 back to 100 is about −9.09%, so opposite rupee movements do not create equal percentage rates.
Common mistakes
- Treating RSI above a threshold as a compulsory sell instruction.
- Counting several price-derived indicators as independent evidence.
What does a high RSI directly describe?
Make this chapter useful
Can you defend the reasoning?
Before moving on, answer the self-check in your own words and write why each alternative fails. Use the worked example to test that explanation. Then apply it in the module research task; keep the assumptions and the evidence that could change your answer.
Sources and further reading
- SEBI investor education ↗
- NISM: Research Analyst learning topics (scope reference; independent lessons) ↗
- CME Group: technical analysis of commodity prices ↗
- Bailey et al.: The Probability of Backtest Overfitting ↗
Further-reading references from the curriculum source list. Contract sizes, expiry calendars, settlement references, margin parameters and tax treatment can change; verify the current operative documents for the actual product. Worked figures are illustrative, not current quotes.
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