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Psychology

Intervention bias

By Jarosław Wasiński • Published: • Updated:
A tendency to act or alter actions for a sense of control without a plan-based reason. Not every manual intervention is wrong; exceptional procedures may require one. Comparison with an unchanged variant can assess effects, but is a counterfactual model rather than always a certain cost.
Example. A plan exits at +2R or −1R. You close from concern at +0.3R; the later path reaches +2R. The +1.7R difference belongs to that counterfactual model, not proof that every intervention harms performance. Available data, execution and every qualifying case must be considered.

Action is not always a breach

Intervention bias describes acting to create a sense of control. A manual exit can be legitimate when the plan permits a response to failure, a specification change or a portfolio limit. Define allowed interventions beforehand. An operational problem differs from temporary discomfort caused by a price movement.

The planned variant is counterfactual

For each intervention, record time, reason and available information. Reconstruct the unchanged variant using the same underlying history and costs. Reconstruction may be ambiguous, for example when OHLC does not identify SL/TP sequence. Report that uncertainty rather than assign one certain intervention cost or assume the planned fill was executable.

Process and effect

Measure breach frequency, deviation from the plan and the distribution of net differences, including beneficial cases. One avoided loss does not justify constant rule changes; one missed winner does not prohibit every intervention. Evaluate a revised policy as a system variant on observations separate from those that inspired it.

FAQ

Does every manual change harm an automated system?
No. It may follow an approved exceptional-case procedure; an unplanned change needs separate assessment.
Is the outcome difference a certain intervention cost?
Not always. It depends on the counterfactual model and available execution history.

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Jarosław Wasiński

Editor-in-chief, ForexMechanics.com • Macro & FX analyst

Independent analyst and practitioner with over 20 years of experience in financial markets. Actively involved in Forex since 2007, with a focus on fundamental analysis, OTC market structure, and disciplined capital risk management.

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