Model, Strategy and System
In trading literature, the terms model, strategy and trading system are often used with different meanings depending on the author or research approach. There is no universally accepted standard that clearly separates these concepts.
For educational purposes, and to provide a consistent framework throughout the TradingQuant website, this article adopts the following distinction:
Market Model → Trading Strategy → Trading System
This progression reflects the natural evolution of a trading idea: from a theoretical explanation of market behaviour, to a set of operational rules, and finally to a complete decision-making framework.
Understanding these differences helps distinguish an interesting hypothesis from a structured process that can be objectively evaluated.
The Market Model
A market model is a simplified explanation of a recurring market phenomenon. It attempts to describe why a particular behaviour may exist and under which conditions it may persist.
Models do not generate trading signals by themselves. Instead, they provide the conceptual foundation upon which trading ideas can be developed.
Examples of market models include:
- Momentum, which assumes that persistent price movements have a tendency to continue.
- Mean reversion, which assumes that temporary price dislocations tend to revert towards an equilibrium.
- Volatility expansion, where periods of low volatility are often followed by larger price movements.
- Seasonal and calendar effects, based on recurring patterns associated with time.
- Behavioural models, which explain market anomalies through recurring patterns in investor behaviour.
A model answers questions such as:
- Under which market conditions could it appear?
It does not answer practical trading questions such as when to enter, when to exit or how much capital to allocate. A model is a research hypothesis, not an operational methodology.
The Trading Strategy
A trading strategy translates a market model into a set of objective trading rules. Different strategies can originate from exactly the same model. For example, a momentum model may generate completely different strategies:
- buying 20-day breakouts;
- buying stocks with the highest relative strength;
- trading moving average crossovers;
- entering after volatility contractions followed by directional expansion.
Although these strategies are different, they all attempt to exploit the same underlying market behaviour.
A strategy typically defines:
- the tradable universe;
- entry conditions;
- exit conditions;
- filters;
- time horizon.
At this stage, the original hypothesis becomes measurable. Historical data can be used to evaluate whether the rules produced results that are statistically meaningful. However, a strategy alone is not yet a complete trading process.
The Trading System
A trading system integrates a trading strategy into a broader operational framework. Beyond entry and exit rules, it specifies how the strategy is implemented, monitored and managed over time.
A complete system typically includes:
- objective trading rules;
- position sizing methodology;
- risk management;
- execution assumptions, including transaction costs and slippage;
- performance evaluation metrics;
- robustness and stability testing;
- monitoring and review procedures.
The transition from strategy to system requires considerably more than a successful backtest.
A robust system should remaining reasonably stable under parameter variations. Out-of-sample testing, sensitivity analysis and robustness checks are essential to reduce the risk of overfitting and to assess whether historical performance is likely to reflect a genuine market characteristic rather than random chance.
Importantly, a system does not have to be complex. Even a relatively simple strategy can become a robust trading system if it is implemented within a disciplined and thoroughly validated process.
Beyond the Idea
Most successful research begins with a simple observation.
The real challenge is not generating ideas, but transforming those ideas into processes that are measurable, repeatable and robust.
- Models provide the theoretical explanation.
- Strategies convert that explanation into operational rules.
- Trading systems integrate those rules into a disciplined framework capable of adapting to real-world market conditions.
Understanding these distinctions provides a more structured way of approaching trading research and helps separate interesting concepts from methodologies that can be objectively evaluated over time.
