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Annals of Internal Medicine
The Effectiveness of a Primer to Help People Understand Risk
Two Randomized Trials in Distinct Populations

Steven Woloshin, MD, MS; Lisa M. Schwartz, MD, MS; and H. Gilbert Welch, MD, MPH
Background: People need basic data interpretation skills to under-
point validated scores (interest and confidence in interpreting med- stand health risks and to weigh the harms and benefits of actions ical statistics) and participants' ratings of the booklet's usefulness.
meant to reduce those risks. Although many studies documentproblems with understanding risk information, few assess ways to Results: In the high SES trial, 74% of participants in the primer
teach interpretation skills.
group received a "passing grade" on the medical data interpreta-tion test versus 56% in the control group (P ⫽ 0.001). Mean scores Objective: To see whether a general education primer improves
were 81 and 75, respectively (P ⫽ 0.0006). In the low SES trial, patients' medical data interpretation skills.
44% versus 26% "passed" (P ⫽ 0.010): Mean scores were 69 and62 in the primer and control groups, respectively (P ⫽ 0.008). The Design: Two randomized, controlled trials done in populations with
primer also significantly increased interest in medical statistics by 6 high and low socioeconomic status (SES).
points in the high SES trial (a 4-point increase vs. a 2-point decrease Setting: The high SES trial included persons who attended a public
from baseline) (P ⫽ 0.004) and by 8 points in the low SES trial (a lecture series at Dartmouth Medical School, Hanover, New Hamp- 6-point increase vs. a 2-point decrease from baseline) (P ⫽ 0.004) shire; and the low SES trial included veterans and their families from compared with the control booklet. The primer, however, did not the waiting areas at the White River Junction Veterans Affairs improve participants' confidence in interpreting medical statistics Medical Center, White River Junction, Vermont.
beyond the control booklet (a 2-point vs. a 4-point increase in thehigh SES trial [P ⫽ 0.36] and a 2-point versus a 6-point increase in Participants: 334 adults in the high SES trial and 221 veterans and
the low SES trial [P ⫽ 0.166]). The primer was rated highly: 91% of their families in the low SES trial were enrolled from October 2004 participants in the high SES trial found it "helpful" or "very help- to August 2005. Completion rates for the primer and control ful," as did 95% of participants in the low SES trial.
groups in each trial were 95% versus 98% (high SES) and 85%versus 96% (low SES).
Limitations: The primarily male low SES sample and the primarily
female high SES sample limits generalizability. The authors did not
Intervention: The intervention in the primer groups was an edu-
assess whether better data interpretation skills improved decision- cational booklet specifically developed to teach people the skills needed to understand risk. The control groups received a generalhealth booklet developed by the U.S. Department of Health and Conclusion: The primer improved medical data interpretation skills
Human Services Agency for Health Care Research and Quality.
in people with high and low SES.
Measurements: Score on a medical data interpretation test, a pre-
Ann Intern Med. 2007;146:256-265.
viously validated 100-point scale, in which 75 points or more is For author affiliations, see end of text.
considered "passing." Secondary outcomes included 2 other 100- registration number: NCT00380432.
People face a bewildering array of medical decisions (for the risk for a particular condition compare with other im-
example, should I be tested for BRCA1? Should I be portant health risks?). Third, people need to be able to screened for prostate cancer? Should I have lumpectomy make some basic assessment about the quality of the evi- and radiation to treat my breast cancer?). If people are to dence to know whether they can believe the numbers that make informed decisions, they need to understand risk: they are given.
What is my chance of staying healthy if I undergo this Anecdotal experience and a growing body of literature intervention? What is my chance of staying healthy if I document the trouble many people have in making sense forgo it? What is the chance of harm? of risk information (1– 4), which is now ubiquitous in Understanding risk data entails a set of skills. First, health messages. This is not surprising: Much more effort people must be able to work with probabilities and changes goes into disseminating health information (for example, in probabilities, the typical measures used to communicate drug advertisements, media reports, and decision-making risk information. Next, they need to have a framework on aids) than into preparing the target audiences to under- which to organize data. In essence, this means having asense of what additional information is needed to givemeaning to a statement about probability (conversely, how to know when such additional information is lacking). For example, putting a particular risk in context ("your chance of breast cancer is 1 in 8") entails knowing what outcomeis being considered (diagnosis vs. death), being clear about the time period (5 years vs. lifetime), and having some Conversion of figures and tables into slides perspective on the magnitude of the probability (How does 256 20 February 2007 Annals of Internal Medicine Volume 146 • Number 4
Testing a Primer on Risk Article stand it. To address this gap, we developed a primer tohelp people develop the basic skills needed to make sense of the medical risk data that surround them. In this paper, Educational materials aimed at improving people's ability we report on 2 randomized trials that tested the primer.
to understand information about risk are scarce.
We sought to learn how people would respond to the primer: Would they read it? Would they value this knowl-edge? Most important, would the primer improve patients' In 2 trials, adults with high or low socioeconomic status abilities to interpret medical data? (SES) were randomly assigned to receive a primer aboutunderstanding risk or a general health booklet. In both SES groups, adults receiving the primer more often passed a medical data interpretation test than did those receivingthe general health booklet. They also expressed greater To test the effect of the primer on how well people interest in medical statistics but not greater confidence in understand risk, we conducted 2 randomized trials in dis- interpreting statistics, and most rated the primer helpful or tinct populations: people with high and low socioeconomic very helpful.
status (SES). Figure 1 shows an overview of the study de-
sign. The Committee for the Protection of Human Sub-
jects at Dartmouth College approved this project, and the The authors did not examine whether improved data in- survey cover letter was considered to be informed consent terpretation skills affected decision-making.
(signed consent was waived).
Setting and Participants
—The Editors We calculated our sample size under the most conser- vative conditions—when the pooled proportion of passingscores was 50%. We asserted that a 20-percentage point erans Affairs (VA) Medical Center, White River Junction, absolute difference in the proportion passing the test in the Vermont, by posting study advertisements in waiting areas primer group versus the control group would be clinically of the outpatient clinic. A total of 221 people who re- important. In calculating the sample size requirements, we sponded to the advertisement were eligible (that is, they therefore assumed that the proportion passing would be met the age criteria of 35 to 79 years, spoke English, and 50% in the control group and 70% in the primer group.
were a veteran or the family member of a veteran who was When a power of 0.8 and a 2-sided P value of 0.05 were enrolled in a VA clinic) and were subsequently randomly used, 100 patients were required for each study group.
assigned. Ninety percent (n ⫽ 200) returned completed Assuming that 10% of participants would be lost to follow- surveys (completion rates were significantly lower in the up, we planned to enroll 110 patients per group in each trial.
primer group than in the control group [85% vs. 96%,respectively]) (P ⫽ 0.005).
High Socioeconomic Status Trial
Randomization and Interventions
To study the effect of the primer in a highly educated The letter and the advertisement asked people to par- and affluent group, we recruited alumni from Dartmouth's ticipate in a research study to learn how to better give "Community Medical School." This 9-lecture series on people health information. We did not mention our inter- various health and medical topics is taught by Dartmouth est in enhancing quantitative skills. People who responded faculty and guests; is held annually in Hanover, New to the recruitment letter (high SES group) or to the adver- Hampshire, and Manchester, New Hampshire; and has a tisement (low SES group) were first interviewed to confirm $25 registration fee (5). For this study, the program orga- eligibility. We only accepted 1 participant per household.
nizers mailed recruitment letters to 1138 "alumni." A total Within each trial, we assigned participants on an individ- of 334 people who responded to the letter were eligible ual basis to receive either the primer or control booklet. A (that is, they met the age criterion of 35 to 79 years, spoke list of random numbers (created by using a random-num- English, and had attended the Community Medical School ber generator) was given to a research assistant and was in the past) and were subsequently randomly assigned.
used to determine assignments (randomization was not Ninety-six percent (n ⫽ 322) returned a completed survey stratified or blocked within each trial). The research assis- (completion rates were not significantly different between tant had access to participants' characteristics. The investi- the primer and control groups [95% vs. 98%, respec- gators did not have access to the assignment list, and the tively]) (P ⫽ 0.192).
deidentified code was only revealed after recruitment andcompletion of data collection.
Low Socioeconomic Status Trial
The appropriate booklet and a survey were mailed or To study the effect of the primer in a sample with given in person to participants. The survey included the lower income and less formal education, we recruited vet- major outcomes that will be described in the next section.
erans and their families at the White River Junction Vet- To make the survey seem relevant to the control group, it 20 February 2007 Annals of Internal Medicine Volume 146 • Number 4 257
Article Testing a Primer on Risk Figure 1. Overview of 2 randomized trials in distinct populations.
SES ⫽ socioeconomic status; VA ⫽ Veterans Affairs.
also included additional questions about facts presented in harms of interventions by using a Zocor direct-to-con- the health booklet (we did not analyze responses to these sumer advertisement for secondary heart disease preven- questions). All participants were asked to read the booklet tion. Figure 2 shows the summary of main concepts that
and return the completed survey within 2 weeks using the were taught, which is excerpted from the booklet. The self-addressed stamped envelope included with the survey.
contents of the primer and many of the examples have Reminder letters were sent to nonresponders. Participants been developed and revised over years of teaching and who returned surveys were given their choice of a $25 gift through focus groups with people across a diverse socioeco- certificate to a local bakery, restaurant, bookstore, or large nomic spectrum.
retail store. We recruited participants from October 2004 Because many people are intimidated by numbers and through August 2005.
statistics, we worked hard to make the primer inviting and Primer Group
nonthreatening by liberal use of cartoons and figures; by The participants in the primer group received the working through examples, separating the most technical booklet entitled "Know Your Chances: Understanding material into optional "learn more boxes"; and by provid- Health Statistics." The goal of the primer is to teach people ing readers with quizzes (with answers) to assess their mas- how to understand risk messages and health statistics. The tery of the material as they read the primer. Figure 3 shows
first part of the primer teaches people how to understand sample pages from the primer. Most of the primer is writ- disease risk by using the example of colon cancer. The ten at the eighth-grade or lower reading level (6) and is a second part focuses on how to understand the benefits and color document approximately 80 pages in length.
258 20 February 2007 Annals of Internal Medicine Volume 146 • Number 4
Testing a Primer on Risk Article Table 1. Baseline Characteristics of Participants in the High Socioeconomic Status and Low Socioeconomic Status Trials*
High SES Trial (n 322)
Low SES Trial (n 200)
Primer Group
Primer Group
(n 169)
(n 153)
(n 102)
(n 98)
Mean age, y (range)
Household income, %
$10 000–$24 999 $25 000–$49 999 $50 000–$99 999 Highest level of education, %
⬍High school graduate High school graduate Postgraduate degree Health status, %
Medical conditions, %
Heart or vascular disease History of any type of cancer Current smoker, %
Mean score on attitudes
Confidence interpreting * The results are for completers only. Percentages may not add to 100% because of rounding. Item nonresponse for high and low SES trials, respectively, were age, 1% and1%; sex, 0% and 0%; income, 6% and 4%; education, 0.4% and 0.5%; race, 0.4% and 0.5%; health status, 1% and 1%; medical conditions, 0% and 0%; smoking, 0%and 0.5%; interest in statistics, 2% and 3%; and confidence, 0.7% and 0.5%. COPD ⫽ chronic obstructive pulmonary disease; SES ⫽ socioeconomic status.
† Scored on scales of 0 to 100 where higher scores represent higher interest or confidence.
Measurement and Outcomes
The control group received a 70-page booklet entitled All outcome measures were assessed in the survey.
"The Pocket Guide for Good Health for Adults," which is published by the U.S. Department of Health and Human The primary outcome was a measure of participants' Services Agency for Health Care Research and Quality (7).
abilities to interpret medical statistics. To measure this out- We chose this booklet because the length is similar to that come, we developed the 18-item data interpretation test of the primer, it is written at a similar reading level (eighth during the same time as the primer and validated it in a grade or lower) (6), and it contains general information separate study (8). The test is available at www.vaoutcomes about risk and reducing risk by following recommended .org/research_tools.php. It extends our original 3-item nu- prevention or screening activities. However, it does not merical measure (4) to include a much broader set of skills include training on how to interpret quantitative informa- beyond simple mathematical manipulation: such skills are the ability to compare risks, to put risk estimates into con- 20 February 2007 Annals of Internal Medicine Volume 146 • Number 4 259
Article Testing a Primer on Risk Figure 2. Key concepts taught in the primer, excerpted from the final pages.
text, and to know what additional information is necessary eligibility interview) and again as part of the survey. These to give meaning to a medical statistic. The data interpreta- previously validated measures (STAT-interest and STAT- tion test does not test recall of facts; instead, it asks people confidence scales) are also scored on 0 to 100 scales in to interpret real-world information (for example, drug ad- which higher scores represent higher interest or confidence vertisements and news stories). The skills being tested are (9). In addition, we asked participants to rate each booklet the same as those in the primer because we feel that they on various dimensions (for example, Did you find it help- are key skills for people to understand. However, the med- ful? Did you learn something new?, and Would you rec- ical data interpretation test requires that the respondent ommend it to others?).
apply these skills to data (within various messages) that donot appear in the primer.
Scores from this test range from 0 to 100 — higher The main results were based on complete case analysis scores represent higher abilities. We consider a score of 75 with additional sensitivity analyses to address the impact of or higher as "passing" and a score of 90 or higher as "out- missing data. We used the chi-square test to compare dif- standing" (the latter threshold corresponds to the mean ferences in proportions and t-tests to compare means. All score of physician experts who teach "evidence-based" comparisons were 2-sided and were considered statistically sig- medicine in our validation study [8]).
nificant at P values less than 0.05. We used Stata, version 9.1(Stata Corp., College Station, Texas) for all analyses.
Role of the Funding Sources
Secondary outcomes included measures of interest and Drs. Woloshin and Schwartz are supported by Robert confidence in interpreting medical statistics. These out- Wood Johnson Generalist Faculty Scholars Awards and comes were assessed twice: before randomization (at the receive infrastructure support from a Research Enhance- 260 20 February 2007 Annals of Internal Medicine Volume 146 • Number 4
Testing a Primer on Risk Article ment Award from the Department of Veterans Affairs. The a household income of $50 000 or greater and 80% had a study was supported by a grant from the National Cancer college or postgraduate degree. In the low SES trial, approxi- Institute (R01CA104721). The funding sources did not mately 70% had a household income less than $50 000 and play a role in the design, data collection, analysis, or inter- approximately 50% had a high school degree or less formal pretation of the study. The authors had full access to the education. As expected, participants in the low SES trial were data files for this study.
mostly men (recruitment was done at a VA hospital) and theparticipants in the high SES trial were mostly women (as has typically been the case at the Dartmouth Community Medi- cal School). The participants in the low SES trial had lower Table 1 summarizes the characteristics of the partici-
self-reported health status, were more likely to smoke, and had pants who completed the survey. As designed, the 2 trials more medical conditions than those in the high SES trial.
had different participants. In the high SES trial, 70% had Within each trial, however, there were no statistically signifi- Table 2. Participants' Ratings of the Primer and Control Booklets*
Booklet Use
High SES Trial
Low SES Trial
Primer Group
Primer Group
(n 169), %
(n 153), %
(n 102), %
(n 98), %
About how much time did you
spend reading the booklet?
Was the booklet easy or hard to
Value of booklet
How helpful was the booklet? I plan to refer to the booklet when I make medicaldecisions in the future I will recommend the booklet to I wish I had read the booklet I learned something new * The results are for completers only. Completion rates for the control and primer groups were as follows: 98% vs. 95% (high SES trial) and 96% vs. 85% (low SES trial).
Percentages may not add to 100% because of rounding. Item nonresponse for the high and low SES trials, respectively, were time, 2.3% and 2.5%; difficulty, 0.4% and 3%;helpfulness, 1% and 2.5%; refer to later, 1.9% and 1.5%; recommend to others, 1.6% and 2%; read before, 1.9% and 1.5%; and learned, 1% and 1.5%. SES ⫽ 20 February 2007 Annals of Internal Medicine Volume 146 • Number 4 261

Article Testing a Primer on Risk Figure 3. Excerpts of primer.
262 20 February 2007 Annals of Internal Medicine Volume 146 • Number 4
Testing a Primer on Risk Article Figure 4. Medical data interpretation scores (mean and proportion exceeding threshold) for the primer and control groups.
SES ⫽ socioeconomic status.
cant differences between the primer and control groups re- To assess the effect of nonresponse on our findings, we garding any characteristic assessed.
considered various possibilities of pass rates among the Primary Outcome: Medical Data Interpretation Skills
nonresponders. Assuming that nonresponders have lowerdata interpretation skills, the most plausible "worst-case" In both trials, the primer resulted in higher medical scenario is that the nonresponders would have failed the data interpretation scores than did the control booklet test. In this case, the statistical significance of the low SES (Figure 4). In the high SES trial, the mean score was 81 in
trial becomes borderline (37% vs. 25%; P ⫽ 0.057) but the primer group versus 75 in the control group—a remains significant in the high SES trial (70% vs. 54% ).
6-point difference (P ⫽ 0.0006). In terms of score thresh- In the least plausible and most extreme "worst-case" sce- olds, 74% of participants in the primer group received a nario (assuming that all of the nonresponders in the primer "passing grade" (score ⱖ75) versus 56% of participants in group would have failed the test but that all nonresponders the control group (P ⫽ 0.001). Twenty-six percent of par- in the control group would have passed the test), the dif- ticipants in the primer group received an "outstanding ference in pass rates in the low SES trial becomes nonsig- grade" (score of ⱖ90), which is the mean score of physi- nificant (37% vs. 29%; P ⫽ 0.20), but remains significant cian experts who teach evidence-based medicine in a vali- in the high SES trial (70% vs. 57%).
dation study of this scale versus 7% of participants in thecontrol group (P ⬍ 0.001). In the low SES trial, the mean scores were 69 in the primer group versus 62 in the control Interest and Confidence
group—a 7-point difference (P ⫽ 0.008). Passing grades Interest in medical statistics was significantly higher (6 were 44% versus 26% (P ⫽ 0.010) and outstanding grades points) in the high SES trial (a 4-point increase vs. 2-point were 10% versus 2% in the primer and controls groups, decrease from baseline; P ⫽ 0.004) and by 8 points in the respectively (P ⫽ 0.014). Finally, results were similar in low SES trial (a 6-point increase vs. a 2-point decrease additional analyses that adjusted for age, sex, level of edu- from baseline; P ⫽ 0.004) after exposure to the primer cation, and medical conditions: The difference in mean compared with the control booklet. The primer, however, interpretation scores was 7 points (P ⬍ 0.001) in the high did not improve participants' confidence in interpreting SES trial and 6 points (P ⫽ 0.019) in the low SES trial for medical statistics beyond the control booklet; if anything, the primer versus the control groups, respectively.
confidence improved more with the control booklet: by 2 The specific skills for which participants in the primer points in the high SES trial (a 2-point increase vs. a 4-point group most outperformed those in the control group were increase; P ⫽ 0.36) and by 4 points in the low SES trial (a as follows: recognizing that counts of events without de- 2-point increase vs. a 6-point increase; P ⫽ 0.166).
nominators do not convey risks (77% vs. 59% in the highSES trial and 54% vs. 41% in the low SES trial answered Rating the Booklets
correctly) and knowing that a risk statement applies to you Finally, participants spent substantial time reading the requires knowing about the age and sex in the source data primer and rated it highly (Table 2). In the high SES trial,
for the risk (81% vs. 55% in the high SES trial and 62% 72% of the primer group reported spending an hour or vs. 37% in the low SES trial answered correctly).
more reading the primer, whereas only 28% of the control 20 February 2007 Annals of Internal Medicine Volume 146 • Number 4 263
Article Testing a Primer on Risk group spent that much time reading their booklet (P ⬍ not hard to explain: The primer covered more challenging 0.001). Similarly, in the low SES trial, 74% of the primer material (it required readers to do math) than did the con- group spent an hour or more reading the primer, whereas trol book. However, completion rates were high overall 47% of the control group spent this much time reading (95% vs. 98% in the high SES trial and 85% vs. 97% in their booklet (P ⫽ 0.001).
the low SES trial).
In the high SES trial, all ratings were significantly Curiously, although the primer improved ability and higher for the primer group than for the control group. For stimulated general interest in medical statistics, it did not example, 91% found the primer "helpful" or "very helpful" increase participants' confidence in interpreting these sta- versus 69% for the control booklet (P ⬍ 0.001). In the low tistics any more than did the control booklet. This finding SES trial, the primer ratings were high but were not statis- probably reflects the educational impact of the primer. For tically different from the ratings of the control booklet. For some people (especially those with the least formal educa- example, 94% and 90% of participants rated the primer tion), acquisition of new data interpretation skills may and control booklet "helpful" or "very helpful," respec- highlight what they did not know before and may expose tively (P ⫽ 0.26).
No analyses, including those for the secondary out- How big was the change in data interpretation skills? comes and booklet ratings, include participants who did Because readers may be unfamiliar with our main outcome not complete the survey. Because completion rates were measure, they may have trouble gauging the clinical signif- lower in the primer group versus the control group in the low icance of our results. One way to put our findings into SES trial (85% vs. 96%), the secondary outcomes and booklet perspective is to consider the distribution of medical data ratings may favor the primer group to the extent that nonre- interpretation skills observed in our previous validation sponders had a less favorable response to the primer.
study. In that study, the average difference in scores be-tween experts (medical school faculty who teach evidence- based medicine) and other respondents with postgraduate We developed and tested a general education primer degrees (similar educational attainment but no relevant ex- designed to teach people basic medical data interpretation pertise) was 20 points (8). The 6- and 7-point differences skills. The primer improved these skills in 2 distinct pop- observed in the present study correspond to gaining ap- ulations: participants with high SES and a demonstrated proximately one third of the difference. Another way to interest in health information (that is, they had attended a put our findings into perspective is to consider the magni- "community medical school" lecture series) and those with tude of the primer's effect in relation to other educational generally low formal education and limited quantitative interventions. One way to make comparisons across inter- skills. Participants liked the primer: A substantial majority ventions is to translate our findings into generic "effect of participants in both trials said they found it useful, it size" units by using a metric called Cohen's d (primer mi- taught them something new, and that they would recom- nus control medical data interpretation scores divided by mend it to others.
the pooled standard deviation of the scores) (10). Our re- Our findings have several limitations. First is the ques- sults correspond to Cohen's d effect sizes of 0.38 (high tion of generalizability. Our study samples were chosen SES) and 0.42 (low SES); by convention, these effect sizes deliberately to ensure the participation of people across a are considered to be between "small" and "medium," the broad spectrum of age, income, and formal education. Be- range covering many successful educational interventions cause almost all participants were white and English speak- (11). For context, on average, taking a practice examina- ers, we cannot be certain how the primer would perform in tion is associated with an approximate 0.30-effect size unit a more ethnically diverse setting. Also, because all partici- increase on standardized test scores (12).
pants were paid—those recruited from an actual health Finally, it is important to acknowledge that although care setting and those recruited from the community—we we have demonstrated that exposure to the primer im- cannot be certain how unpaid persons would respond to proved medical data interpretation skills, we did not prove the primer. Second, there may be concern regarding the that the primer leads to better decision-making. Because appropriateness of the control booklet. We chose an edu- informed decision-making is not possible without under- cational booklet (7) (published by the U.S. Department of standing the relevant facts, we think improving data inter- Health and Human Services Agency for Healthcare Re- pretation skills is clearly a legitimate outcome in itself and search and Quality) that was similar to the primer in length a necessary prerequisite to making good decisions.
and tone. Because the control booklet did not teach readers Implementing the primer, like decision aids, guide- about interpreting risk, it worked as a "placebo" with re- lines, or research innovations in general (13) may be chal- spect to the main outcome measure (that is, the tests results lenging. We believe there are several ways that the primer on medical data interpretation in the control group should could be used in clinical practice. It might be distributed reflect existing abilities). Third, in both trials, completion either before or after routine clinic visits when patients are rates were lower in the primer group than in the control making decisions regarding screening and prevention. It group, particularly in the low SES trial. This observation is might be even more important for patients facing such 264 20 February 2007 Annals of Internal Medicine Volume 146 • Number 4
Testing a Primer on Risk Article high-stakes decisions as surgery or chemotherapy. It is pos- Requests for Single Reprints: Lisa M. Schwartz, MD, MS, VA Out-
sible that patients facing a new and serious disease (for comes Group (11B), Department of Veterans Affairs Medical Center, example, a new diagnosis of cancer) may have greater mo- White River Junction, VT 05009; e-mail,
tivation to really understand the data regarding benefitsand harms of various interventions and would find the Current author addresses and author contributions are available at
primer very useful. Alternatively, they may feel too emo-tionally overwhelmed to use the primer. If this were thecase, the primer might be useful for families or friends who are helping the patient with decision-making. Questions of 1. Edwards A, Elwyn G. Understanding risk and lessons for clinical risk com-
when and where the primer might be most effectively used munication about treatment preferences. Qual Health Care. 2001;10 Suppl 1:i9- and how the reader's emotional state, decision-making 13. [PMID: 11533431] style, and preferences might influence its impact are clearly 2. Gazmararian JA, Baker DW, Williams MV, Parker RM, Scott TL, Green
a topic for further study.
DC, et al. Health literacy among Medicare enrollees in a managed care organi-
In conclusion, the primer "Know Your Chances: Un- zation. JAMA. 1999;281:545-51. [PMID: 10022111]
3. Kirsch IS, Jungeblut A, Jenkins L, Kolstad A. Adult literacy in America: A
derstanding Health Statistics"—a simple, inexpensive, low- First Look at Results of the National Adult Literacy Survey. Washington, DC: tech intervention—improved medical data interpretation U.S. Government Printing Office; 1993.
skills and was rated highly by well-educated participants as 4. Schwartz LM, Woloshin S, Black WC, Welch HG. The role of numeracy in
well as by those with less formal education.
understanding the benefit of screening mammography. Ann Intern Med. 1997;127:966-72. [PMID: 9412301]5. Dartmouth Community Medical School Home Page. Accessed at http://dms From the Veterans Affairs Outcomes Group, White River Junction, Ver- on 14 December 2006.
mont, and the Center for the Evaluative Clinical Sciences, Dartmouth 6. Microsoft Corporation. Microsoft Word X. Flesch-Kincaid Readability Statis-
Medical School, Hanover, New Hampshire.
tics. Redmond, WA: Microsoft Corporation; 1983-2001.
7. Agency for Healthcare Research and Quality. The pocket guide for good
Disclaimer: The views expressed herein do not necessarily represent the
health for adults. Accessed at on 14 September views of the Department of Veterans Affairs or the U.S. government.
8. Schwartz LM, Woloshin S, Welch HG. Can patients interpret health infor-
Note: The first two authors contributed equally to the creation of this
mation? An assessment of the medical data interpretation test. Med Decis Mak- manuscript. The order of authorship is arbitrary.
ing. 2005;25:290-300. [PMID: 15951456]
9. Woloshin S, Schwartz LM, Welch HG. Patients and medical statistics. Inter-
Acknowledgments: The authors thank Donald St. Germaine, MD, and
est, confidence, and ability. J Gen Intern Med. 2005;20:996-1000. [PMID: Wendy Murphy for their assistance in recruiting Dartmouth Commu- nity Medical School alumni; Jennifer A. Snide for technical assistance; 10. Thalheimer W, Cook S. How to calculate effect sizes from published research
and Baruch Fischhoff, PhD, and Wylie Burke, MD, PhD, for helpful articles: a simplified methodology. Accessed at on 14 September 2006.
comments on earlier drafts of the primer.
11. Valentine J, Cooper H. Effect size substantive interpretation guidelines: Is-
sues in the interpretation of effect sizes. Washington, DC: What Works Clear-
Grant Support: Drs. Woloshin and Schwartz are supported by Robert
inghouse; 2003. Accessed at on Wood Johnson Generalist Faculty Scholars Awards and receive infra- 15 September 2006.
structure support from a Research Enhancement Award from the De- 12. Kulik JA, Kulik CLC, Bangert RL. Effects of practice on aptitude and
partment of Veterans Affairs. The study was supported by a grant from achievement test scores. Am Educ Res J. 1984;21:435-47. Accessed at www.jstor the National Cancer Institute (R01CA104721).
.org/view/00028312/ap040083/04a00130/0 on 14 December 2006.
13. Haines A, Jones R. Implementing findings of research. BMJ. 1994;308:
Potential Financial Conflicts of Interest: None disclosed.
1488-92. [PMID: 8019284] 20 February 2007 Annals of Internal Medicine Volume 146 • Number 4 265
Annals of Internal Medicine
Current Author Addresses: Drs. Woloshin, Schwartz, and Welch: VA
Drafting of the article: S. Woloshin, L.M. Schwartz, H.G. Welch.
Outcomes Group (11B), Department of Veterans Affairs Medical Cen- Critical revision of the article for important intellectual content: S.
ter, White River Junction, VT 05009.
Woloshin, L.M. Schwartz.
Final approval of the article: S. Woloshin, L.M. Schwartz, H.G. Welch.
Author Contributions: Conception and design: S. Woloshin, L.M.
Provision of study materials or patients: S. Woloshin, L.M. Schwartz.
Schwartz, H.G. Welch.
Statistical expertise: S. Woloshin, L.M. Schwartz.
Analysis and interpretation of the data: S. Woloshin, L.M. Schwartz, Obtaining of funding: S. Woloshin, L.M. Schwartz.
20 February 2007 Annals of Internal Medicine Volume 146 • Number 4 W-69


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