What it means
An investor may find it easier to realize a gain than to accept a loss. That pattern is called the disposition effect when it shows up as a greater tendency to sell positions trading above their purchase prices than positions trading below them. The purchase price is a reference point, not necessarily evidence about what a stock is worth now.
The pattern can be associated with loss aversion: realizing a loss can feel different from continuing to hold an unrealized one. But a sale of a winner or continued holding of a loser does not, by itself, establish bias. Taxes, portfolio targets, cash needs and changes in risk can provide independent reasons for either choice.
How it is calculated
There is no single diagnostic score for an individual decision. One way to measure the pattern across a trading history is to compare the proportion of gains realized with the proportion of losses realized:
Disposition measure = PGR − PLR
PGR = realized gains / (realized gains + paper gains). Realized gains are positions sold above their purchase price; paper gains are positions still held above it.PLR = realized losses / (realized losses + paper losses). Realized losses are positions sold below their purchase price; paper losses are positions still held below it.
These are counts of positions classified under a consistent method, not dollar amounts or percentage returns. The measure is in percentage points if PGR and PLR are expressed as percentages. A positive result means gains were realized more frequently than losses in the observations; it does not prove why. If either denominator is zero, the comparison is undefined. Transaction costs and dividends are not captured by this simple purchase-price classification.
Worked example
Consider a hypothetical investor's observations over a period. Assume each position is counted once under the same method, and ignore costs, dividends and taxes:
- Of 20 positions above purchase price, 12 are sold and 8 remain held.
PGR = 12 / (12 + 8) = 60%. - Of 20 positions below purchase price, 4 are sold and 16 remain held.
PLR = 4 / (4 + 16) = 20%. Disposition measure = 60% − 20% = 40 percentage points.
This history shows more frequent realization of gains than losses. It does not show that any specific trade was mistaken or that holding the losing positions caused a particular return. The observations also depend on when positions were checked and how partial sales were counted.
Why it matters before you trade
A proposed sale may be driven partly by the satisfaction of locking in a gain; a decision to keep a position may be driven partly by reluctance to realize a loss. Before placing an order, a useful question is whether the same decision would make sense if the purchase price were hidden. Compare the position's current risk, concentration, costs and role in the portfolio with the investor's stated objectives and constraints.
The check works in both directions. Avoiding a loss is not automatically a reason to hold, and showing a gain is not automatically a reason to sell. A documented reason independent of the entry price makes the decision easier to review later.
How PreTrAIde uses it
PreTrAIde is not stated to calculate a disposition-effect measure or diagnose behavioral bias. Its pre-trade analysis examines a proposed stock basket before an order is placed, including each line's side, quantity and execution conditions. It provides basket-level and line-level GO, NO-GO or MODIFY verdicts, risk assessments and plain-language reasoning as decision support, not recommendations.
A separate check of purchase-price bias can complement that analysis. Users can also log what they actually executed in PreTrAIde Memory, but the product facts do not state that this log measures the disposition effect.
Common mistakes
- Treating every sale at a gain or hold at a loss as irrational. The reason for the decision matters.
- Treating an unrealized loss as economically harmless. The position's current value and risks still matter.
- Reading a positive disposition measure as proof of loss aversion. It describes observed selling frequencies, not motive.
- Comparing counts from inconsistent periods or counting partial sales differently across positions.