How many impulsivities? A discounting perspective.
Delay and probability discounting are not the same trait—assess both before you write a behavior plan.
01Research in Context
What this study did
Green et al. (2013) reviewed dozens of discounting studies. They asked: do delay and probability discounting measure the same thing?
They concluded the two tasks tap different kinds of impulsivity. One is about waiting. The other is about risk.
What they found
The paper says there is no single trait called impulsivity. Instead, there are multiple impulsivities.
A child who hates waiting may not be the child who loves risk. You need two tests, not one.
How this fits with other research
Rung et al. (2019) extends the idea. They show delay discounting can be trained down with simple games. Traits can move.
Green et al. (2019) seems to clash. They argue steep discounting is a context reaction, not a trait. The fight is real.
Paglieri et al. (2015) deepens the puzzle. They warn that low motivation can look like high impulsivity. Check what the client wants before you label them.
Why it matters
Stop using one score to sum up impulsivity. Give both a delay task and a probability task. If scores differ, write two goals, not one.
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02At a glance
03Original abstract
People discount the value of delayed and uncertain outcomes, and how steeply individuals discount is thought to reflect how impulsive they are. From this perspective, steep discounting of delayed outcomes (which fails to maximize long-term welfare) and shallow discounting of probabilistic outcomes (which fails to adequately take risk into account) reflect the same trait of impulsivity. Despite the fact that a hyperboloid function describes the discounting of both delayed and probabilistic outcomes, there is considerable evidence that the two kinds of discounting involve different processes as well as separate impulsivity traits. Several manipulations differentially affect delay and probability discounting, and correlational studies show that how steeply one discounts delayed rewards is relatively independent of how steeply one discounts probabilistic rewards. Moreover, people's discounting of delayed money and health outcomes are uncorrelated as are discounting of real, consumable rewards and hypothetical money. These results suggest that even within delay discounting, there may be multiple 'impulsivities,' each of which may be important for understanding a different aspect of decision making. Taken together, the pattern of findings reviewed here argues for a more nuanced view of impulsivity than that which is usually assumed in discounting research.
Journal of the experimental analysis of behavior, 2013 · doi:10.1002/jeab.1