Clinical Calculator


Why use numbers?

Physicians have pervasive problems in quantitative reasoning. In particular, physicians have difficulty in diagnosis with Bayesian analyses (1-3), interpreting effectiveness of treatments (4,5), and in estimating probabilities (1-2,6-8). Perhaps as a result, physicians infrequently use probabilities in their clinical practice (9-11).

The consequences of these difficulties may include excessive test ordering (12), incorrect interpretation of test results (13), inconsistent interpretation of qualitative descriptions of probability (14), inconsistent interpretration of absolute versus relative risk(15), inconsistent treatment decisions (1), and over-treatment of conditions that have infrequent bad outcomes 20.

Varous solutions have been studied. Several studies have shown clinical improvements when the use of clinical prediction rules were taught to clinicians (15-21), especially when the prediction rules are integrated into patient care as part of the work flow (19-21). Studies of formal shared decision making suggest that patients are less likely to choose options such as prostate cancer screening after being informed of the actual probabilities of outcomes (22). One randomized trail showed that teaching probabilistic reasoning was associated with decrease tested ordering by physicians (11).


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2. Whiting PF, Davenport C, Jameson C, Burke M, Sterne JA, Hyde C, Ben-Shlomo Y. How well do health professionals interpret diagnostic information? A systematic review. BMJ Open. 2015 Jul 28;5(7):e008155. 26220870.

3. Steinberg EP, Dans PE, Keruly JC, Egbuonu LC. A case study of physicians' use of liver-spleen scans. Are we doing what we think we're doing? Arch Intern Med 1986;146(2):253-8. PMID: 3947184.

4. Sheridan SL, Pignone MP, Lewis CL. A randomized comparison of patients' understanding of number needed to treat and other common risk reduction formats. J Gen Intern Med 2003;18(11):884-92. PMID: 14687273.

5. Naylor CD, Chen E, Strauss B. Measured enthusiasm: does the method of reporting trial results alter perceptions of therapeutic effectiveness? Ann Intern Med. 1992 Dec 1;117(11):916-21. PMID: 1443954.

6. Friedmann PD, Brett AS, Mayo-Smith MF. Differences in generalists' and cardiologists' perceptions of cardiovascular risk and the outcomes of preventive therapy in cardiovascular disease. Ann Intern Med 1996;124(4):414-21. PMID: 8554250

7. Poses RM, Cebul RD, Wigton RS. You can lead a horse to water--improving physicians' knowledge of probabilities may not affect their decisions. Med Decis Making. 1995 Jan-Mar;15(1):65-75. PMID: 7898300.

8. 1: Agoritsas T, Courvoisier DS, Combescure C, Deom M, Perneger TV. Does prevalence matter to physicians in estimating post-test probability of disease? A randomized trial. J Gen Intern Med. 2011 Apr;26(4):373-8. PMID: 21053091.

9. Reid MC, Lane DA, Feinstein AR. Academic calculations versus clinical judgments: practicing physicians' use of quantitative measures of test accuracy. Am J Med 1998;104(4):374-80. PMID: 9576412.

10. Beasley BW, Woolley DC. Evidence-based medicine knowledge, attitudes, and skills of community faculty. J Gen Intern Med 2002;17(8):632-9. PMID: 12213145

11. Kalet A, Roberts JC, Fletcher R. How do physicians talk with their patients about risks? J Gen Intern Med 1994;9(7):402-4. PMID: 7931751

12. Davidoff F, Goodspeed R, Clive J. Changing test ordering behavior. A randomized controlled trial comparing probabilistic reasoning with cost-containment education. Med Care 1989;27(1):45-58. PMID: 2492066.

13. Redelmeier DA. Improving patient care. The cognitive psychology of missed diagnoses. Ann Intern Med 2005;142(2):115-20. PMID: 15657159.

14. Nakao MA, Axelrod S. Numbers are better than words. Verbal specifications of frequency have no place in medicine. Am J Med 1983;74(6):1061-5. PMID: 6859055.

15. Stiell IG, McKnight RD, Greenberg GH, McDowell I, Nair RC, Wells GA, Johns C, Worthington JR. Implementation of the Ottawa ankle rules. JAMA 1994;271(11):827-32. PMID: 8114236.

16. Stiell I, Wells G, Laupacis A, Brison R, Verbeek R, Vandemheen K, Naylor CD. Multicentre trial to introduce the Ottawa ankle rules for use of radiography in acute ankle injuries. Multicentre Ankle Rule Study Group. BMJ 1995;311(7005):594-7. PMID: 7663253.

17. Auleley GR, Ravaud P, Giraudeau B, Kerboull L, Nizard R, Massin P, Garreau de Loubresse C, Vallee C, Durieux P. Implementation of the Ottawa ankle rules in France. A multicenter randomized controlled trial. JAMA 1997;277(24):1935-9. PMID: 9200633.

18. Stiell IG, Wells GA, Hoag RH, Sivilotti ML, Cacciotti TF, Verbeek PR, Greenway KT, McDowell I, Cwinn AA, Greenberg GH, et al. Implementation of the Ottawa Knee Rule for the use of radiography in acute knee injuries. JAMA 1997;278(23):2075-9. PMID: 9403421.

19. Selker HP, Beshansky JR, Griffith JL, Aufderheide TP, Ballin DS, Bernard SA, Crespo SG, Feldman JA, Fish SS, Gibler WB, et al. Use of the acute cardiac ischemia time-insensitive predictive instrument (ACI-TIPI) to assist with triage of patients with chest pain or other symptoms suggestive of acute cardiac ischemia. A multicenter, controlled clinical trial. Ann Intern Med 1998;129(11):845-55. PMID: 9867725.

20. Marrie TJ, Lau CY, Wheeler SL, Wong CJ, Vandervoort MK, Feagan BG. A controlled trial of a critical pathway for treatment of community-acquired pneumonia. CAPITAL Study Investigators. Community-Acquired Pneumonia Intervention Trial Assessing Levofloxacin. JAMA. 2000 Feb 9;283(6):749-55. PMID: 10683053.

21. Yealy DM, Auble TE, Stone RA, et al. Effect of increasing the intensity of implementing pneumonia guidelines: a randomized, controlled trial. Ann Intern Med. 2005 Dec 20;143(12):881-94. PMID: 16365469.

22. Barry MJ. Health decision aids to facilitate shared decision making in office practice. Ann Intern Med. 2002 Jan 15;136(2):127-35. PMID: 11790064.