3.2. Limits on memory, attention, and computation

In reasoning about social matters, we often attend to a number of different

evidential cues. But we have certain cognitive limits, including limits on

memory, attention, and computation, that could well be implicated in the

relative unreliability of our social judgments. For example, we aren’t very

good at keeping even medium-sized amounts of information available in

attention or memory when solving a problem (Bettman et al. 1990). And

The Amazing Success of Statistical Prediction Rules 39

this prevents us from making accurate predictions on the fly. On the received

view, we attempt to arrive at a solution to a problem by searching the

problem space. For many problems, the size of this space is cognitively unmanageable;

the problem space contains more information than the electric

flesh between our ears can handle at one time. Take the example of chess. If

the goal is to checkmate your opponent, in the early stages of the game the

solution search space is enormous. How do people make the problem

tractable? They adopt a strategy that navigates a limited path through the

search space, a heuristic that identifies a small number of plausible (rather

than all possible) strategies to secure a solution (Newell and Simon 1972).

Daily life confirms that our memory is limited. (We seem to get more

confirmation as we grow older!) It also confirms that our attention is

limited. The so-called ‘‘central limited capacity of attention’’ principle has

been a basic premise of the last 40 years of research on attention. In the

classic divided-attention experiments, observed decrements in performance

are explained in terms of limitations on internal processing (van

der Heijden, 1998). If limitations on attention and memory produce regrettable

performance in simple tasks, why should we suppose that we can,

without fear of embarrassment, use the same feeble tools to accurately

evaluate complex issues of social judgment?

Even if we knew what cues to look for and we could remember them

and we could attend to them, we often find it very difficult to combine

those cues effectively. Paul Meehl makes this point starkly by focusing on a

familiar example:

Surely we all know that the human brain is poor at weighting and computing.

When you check out at a supermarket, you don’t eyeball the heap of

purchases and say to the clerk, ‘‘Well it looks to me as if it’s about $17.00

worth; what do you think?’’ The clerk adds it up. There are no strong

arguments from the armchair or from empirical studies . . . for believing that

human beings can assign optimal weights in equations subjectively or that

they apply their own weights consistently. (Meehl 1986, 372)

Notice that in Meehl’s grocery example, we know that a simple addition is

the right calculation to apply, and the variable values (i.e., the prices) are

usually stamped right on the products. But suppose that the computation

required was much more complex. This of course would make matters

even worse:

Suppose instead that the supermarket pricing rule were, ‘‘Whenever both

beef and fresh vegetables are involved, multiply the logarithm of 0.78 of the

meat price by the square root of twice the vegetable price’’; would the clerk and customer eyeball any better? Worse, almost certainly. When human

judges perform poorly at estimating and applying the parameters of a simple

or component mathematical function, they should not be expected to do

better when required to weigh a complex composite of those variables. (Dawes,

Faust, and Meehl 1989, 1672)

So when it comes to problems of social judgment, we have trouble discovering

the right correlations, remembering their values, attending to

more than just a few of them, and combining the values appropriately to

render a judgment. If this is right, if the basis of our social judgments are

riddled with error and limitations, then why do most people seem to have

so much success in the social world? The sobering answer is probably that

most of us have less success in the social world than we think.

In reasoning about social matters, we often attend to a number of different

evidential cues. But we have certain cognitive limits, including limits on

memory, attention, and computation, that could well be implicated in the

relative unreliability of our social judgments. For example, we aren’t very

good at keeping even medium-sized amounts of information available in

attention or memory when solving a problem (Bettman et al. 1990). And

The Amazing Success of Statistical Prediction Rules 39

this prevents us from making accurate predictions on the fly. On the received

view, we attempt to arrive at a solution to a problem by searching the

problem space. For many problems, the size of this space is cognitively unmanageable;

the problem space contains more information than the electric

flesh between our ears can handle at one time. Take the example of chess. If

the goal is to checkmate your opponent, in the early stages of the game the

solution search space is enormous. How do people make the problem

tractable? They adopt a strategy that navigates a limited path through the

search space, a heuristic that identifies a small number of plausible (rather

than all possible) strategies to secure a solution (Newell and Simon 1972).

Daily life confirms that our memory is limited. (We seem to get more

confirmation as we grow older!) It also confirms that our attention is

limited. The so-called ‘‘central limited capacity of attention’’ principle has

been a basic premise of the last 40 years of research on attention. In the

classic divided-attention experiments, observed decrements in performance

are explained in terms of limitations on internal processing (van

der Heijden, 1998). If limitations on attention and memory produce regrettable

performance in simple tasks, why should we suppose that we can,

without fear of embarrassment, use the same feeble tools to accurately

evaluate complex issues of social judgment?

Even if we knew what cues to look for and we could remember them

and we could attend to them, we often find it very difficult to combine

those cues effectively. Paul Meehl makes this point starkly by focusing on a

familiar example:

Surely we all know that the human brain is poor at weighting and computing.

When you check out at a supermarket, you don’t eyeball the heap of

purchases and say to the clerk, ‘‘Well it looks to me as if it’s about $17.00

worth; what do you think?’’ The clerk adds it up. There are no strong

arguments from the armchair or from empirical studies . . . for believing that

human beings can assign optimal weights in equations subjectively or that

they apply their own weights consistently. (Meehl 1986, 372)

Notice that in Meehl’s grocery example, we know that a simple addition is

the right calculation to apply, and the variable values (i.e., the prices) are

usually stamped right on the products. But suppose that the computation

required was much more complex. This of course would make matters

even worse:

Suppose instead that the supermarket pricing rule were, ‘‘Whenever both

beef and fresh vegetables are involved, multiply the logarithm of 0.78 of the

meat price by the square root of twice the vegetable price’’; would the clerk and customer eyeball any better? Worse, almost certainly. When human

judges perform poorly at estimating and applying the parameters of a simple

or component mathematical function, they should not be expected to do

better when required to weigh a complex composite of those variables. (Dawes,

Faust, and Meehl 1989, 1672)

So when it comes to problems of social judgment, we have trouble discovering

the right correlations, remembering their values, attending to

more than just a few of them, and combining the values appropriately to

render a judgment. If this is right, if the basis of our social judgments are

riddled with error and limitations, then why do most people seem to have

so much success in the social world? The sobering answer is probably that

most of us have less success in the social world than we think.