Using statistical risk information to assess oral contraceptive safety

Abstract

The effect of variations in the presentation of oral contraceptive risk information on perceived safety was investigated. Four tests of the hypothesis that consumers focus on the absolute value of the numbers presented when assessing risk probabilities were performed with the following results: (1) when base rates are given, risks are perceived as less likely than when base rates are not given; (2) risks seem smaller when the information provided focuses on the number that will not die than when the number of expected deaths is presented; ( 3 ) contrary to our expectation, respondents do not focus on foreground numbers when risk was represented in an 'X out of Y occurrences' format; (4) respondents judged a risk of '4.15 times greater' as less likely than when the information was presented as '415% greater risk'. We concluded that consumers convert statistical risk information into judgements about the magnitude of the number presented (small or large number) and utilize this more meaningful information when making risk judgements.Individuals in modern society are frequently required to make decisions that involve grave potential risk. As voters and consumers we have to make 'safe enough' decisions about a large and diverse array of topics which include nuclear energy, food irradiation, surgical procedures, air and water quality, and drug use. There is a large body of psychological research that shows that estimates of the probability of risky events are affected by multiple sources of error. People tend to greatly misuse odds of greater than 50:l (Slovic, Fischoff and Lichtenstein, 1977), underutilize base rates (Einhorn and Hogarth, 198l), interpret mathematically equivalent forms of statistical information in different ways (Halpern and Blackman, 1985), ignore or significantly underestimate the cumulative nature of probabilistic events (Shaklee, 1987), weigh more heavily the testimonials of one or a few people than data generated from large samples (Hogarth, 1980), overestimate events that are readily available in memory and/or appear representative of the underlying phenomenon (Tversky and Kahneman, 1974), and believe that favourable events are more likely to occur than unfavourable ones (Beyth-Marom, Dekel, Gombo and Shaked, 1985;Halpern and Irwin, 1973).Decisions involving oral contraceptives should be immune to many of these difficulties because potential consumers are provided with objective probability 088&4080/89/03025 1-10$05.00 0 1989

Treating People With Information: an Analysis and Review of Approaches to Communicating Health Risk Information

“…Th at is, a 10% risk should be interpreted as a 10% risk, regardless of whether it is presented as a percentage or an odds ratio or whether it is presented numerically or pictorially. Unfortunately, empirical tests of probability-based communications have typically failed to support this premise [e.g., (31,32)]. People have diffi culty recalling probability information accurately [e.g., (33,34)], they make errors when asked to transform percentages into proportions or vice versa (e.g., Lipkus I: unpublished data [numeracy survey], 1998), and they confuse information about the frequency of a event with its rate of occurrence [e.g., (35)].…”

“…Moreover, Yamagishi (42) found that people rated a health problem as riskier when they were informed that it kills 1286 of 10000 people (12.86%) compared with 24.14 of 100 people (24.14%). It would appear that people fail to consider the relevant sample size when processing information regarding the number of people who have developed or died from a health problem [but see (31)]. …”

Asking sensitive questions: The effects of type of referent and frequency wording in counterbiasing methods

“…Subjects tend to pay attention to actual magnitude information, irrespective of the unit of measurement. Halpern et al (1989) demonstrate that subjects perceived "4.15 times greater" to be equivalent to "415% times greater," though the former is actually equivalent to "315% times greater." Further, even though subjects perceive "4.15 times" and "415%" to be equivalent, they judge 415% as a greater risk of death than 4.15 times, based purely on the magnitude of the numbers presented.…”

Health Risk Perceptions and Consumer Psychology

“…For example, respondents have been shown to ignore the format in which numerical information is provided and make judgments based on the absolute magnitudes of the number provided (Halpern, Blackman and Salzman 1989). This led to people perceiving "100% greater" to mean "twice" as large, and "200% greater" to also mean "twice" as large!…”

“…This led to people perceiving "100% greater" to mean "twice" as large, and "200% greater" to also mean "twice" as large! Halpern et al (1989) also showed that "4.15 times greater" was perceived to be equivalent to "415% times greater" rather than the normatively correct "315% times greater." Interestingly, presenting information as a percentage or as number of times (i.e., actual frequency), also affected risk perceptions: though people perceived "4.15 times" to be the same as "415%" they judged 415% to be a greater risk of death than 4.15 times.…”