When Half Is at Least 50%: Effect of “Framing” and Probability Level on Frequency Estimates

Expert judgment often involves estimating magnitudes, such as the frequency of deaths due to a pandemic. Three experiments (Ns = 902, 431, and 755, respectively) were conducted to examine the effect of outcome framing (e.g., half of a threatened group expected to survive vs. die), probability level (low vs. high), and probability format (verbal, numeric, or combined) on the estimated frequency of survivals/deaths. Each experiment found an interactive effect of frame and probability level, which supported the hypothesis that forecasted outcomes received by participants were implicitly quantified as lower bounds (i.e., “at least half”). Responding in a manner consistent with a lower-bound “at least” interpretation was unrelated to incoherence (Experiments 1 and 2) and positively related to numeracy (Experiments 1 and 3), verbal reasoning (Experiment 3), and actively open-minded thinking (Experiments 2 and 3). The correlational results indicate that implicit lower bounding is an aspect of linguistic inference and not a cognitive error. Implications for research on framing effects are discussed.