Base rates: Both neglected and intuitive.

Abstract

Base-rate neglect refers to the tendency for people to underweight base-rate probabilities in favor of diagnostic information. It is commonly held that base-rate neglect occurs because effortful (Type 2) reasoning is required to process base-rate information, whereas diagnostic information is accessible to fast, intuitive (Type 1) processing (e.g., Kahneman & Frederick, 2002). To test this account, we instructed participants to respond to base-rate problems on the basis of "beliefs" or "statistics," both in free time (Experiments 1 and 3) and under a time limit (Experiment 2). Participants were given problems with salient stereotypes (e.g., "Jake lives in a beautiful home in a posh suburb") that either conflicted or coincided with base-rate probabilities (e.g., "Jake was randomly selected from a sample of 5 doctors and 995 nurses for conflict; 995 doctors and 5 nurses for nonconflict"). If utilizing base-rates requires Type 2 processing, they should not interfere with the processing of the presumably faster belief-based judgments, whereas belief-based judgments should always interfere with statistics judgments. However, base-rates interfered with belief judgments to the same extent as the stereotypes interfered with statistical judgments, as indexed by increased response time and decreased confidence for conflict problems relative to nonconflict. These data suggest that base-rates, while typically underweighted or neglected, do not require Type 2 processing and may, in fact, be accessible to Type 1 processing.

What makes us think? A three-stage dual-process model of analytic engagement

“…This finding indicates that both base-rates and stereotypes cue Type 1 outputs (see also Brenner, Griffin, & Koehler, 2012). Under this account, stereotypes typically dominate reasoning because they cue intuitive responses that come to mind more quickly and fluently than the base-rates (Pennycook, Trippas, et al, 2014).…”

“…The claim that base-rate responses are usually accompanied by an active suppression of the salient stereotypical response via Type 2 processing is not the same as claiming that the base-rate response necessarily requires Type 2 processing to enter into reasoning (De Neys, 2007). Indeed, a recent set of experiments using an instruction manipulation illustrated that both base-rates and stereotypes appear to interfere with each other (Pennycook, Trippas, et al, 2014). This cross-interference was evident even when participants were forced to respond within a short time-deadline.…”

“…However, this does not rule out the possibility that alternative sources of information can cue an alternative Type 1 output in parallel. As discussed above, extreme base-rates presented in simple frequency formats influence response time, confidence, and probability estimates in ways diagnostic of Type 1 processing (Pennycook, Trippas, et al, 2014). Thus, base-rate problems serve as an example of a case where two competing sources of information embedded in a problem can elicit competing initial responses (see section 6.5 for further examples).…”

“…Recent research has also indicated that people are implicitly aware of the conflict between base-rate and stereotype, despite the apparent neglect or underweighting of the baserates (De Neys, Comheeke, & Osman, 2011;De Neys & Glumicic, 2008;De Neys, Vartanian, & Goel, 2008), perhaps because extreme probabilities (as shown above) can be processed very rapidly Pennycook & Thompson, 2012;Pennycook, Trippas, Handley, & Thompson, 2014). Importantly for present purposes, one of the key pieces of evidence for the conflict detection hypothesis is an increase in response time (RT) for conflict (as above) versus non-conflict (e.g., if there were 5 nurses and 995 doctors above) base-rate problems even when participants give the stereotypical response 2 .…”

“…In the three-stage model, it is possible for a factor traditionally associated with analytic processing such as base-rate probabilities or logical validity to be the source of a Type 1 output (see Handley & Trippas, 2015) -and, in fact, for some individuals it is quite possible that factors such as logic are more intuitive than factors such as belief (that is, logic cues IR1 and belief cues IR2). Moreover, manipulating problem structure (e.g., the format of base-rates, Evans, Handley, Perham, Over, & Thompson, 2000) or top-down factors such as instructions (Handley, et al, 2011;Pennycook, Trippas, et al, 2014) may alter the initial processing of the problems such that typically more intuitive responses are engendered more slowly (from IR1 to IR2) and typically less intuitive responses are engendered more quickly (from IR2 to IR1). In this way, the three-stage model is capable of accommodating both logical intuitions and effortful beliefs (for an extended discussion, see Handley & Trippas, 2015).…”