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Anticoagulant Patient Information Material Is Written at High Readability Levels

Originally published 2000;31:2966–2970


    Background—Warfarin therapy requires frequent monitoring and dose adjustment. Elderly patients with atrial fibrillation, prior stroke, and lower literacy skills may have difficulty reading brochures that explain dosing instructions, procedures to follow, and the risks and benefits of anticoagulants. In general, it is recommended that brochures be written at or below the 6th-grade level. We determined the readability of patient information material being offered to patients receiving anticoagulants.

    Methods and Results—We used the SMOG grade formula to measure readability of written patient materials. We obtained 50 brochures commonly used in anticoagulation management units from industry and health advocacy groups. Patient information was related to atrial fibrillation (16%, n=8), warfarin (44%, n=22), low-molecular-weight heparins (12%, n=6), or other related topics (28%, n=14). The mean readability was found to be grade 10.7 (95% CI 10.1 to 11.2); none had a readability score at the 6th-grade level or below, 12% of the brochures had readability scores at the 7th- to 8th-grade levels (n=6), 74% at the 9th- to 12th-grade levels (n=37), and 14% at higher than 12th-grade level (n=7). The readability grade level was similar for brochures produced by industry or health advocacy groups (P=0.9) but higher for information obtained from the Internet (12.2±1.3 grades) compared with other sources (10.3±2.1 grades; P=0.01).

    Conclusions—Patient education materials related to the use of anticoagulants are written at grade levels beyond the comprehension of most patients. Low-literacy brochures are needed for patients on anticoagulants.

    Warfarin is indicated in elderly persons with atrial fibrillation to prevent stroke, and its use requires frequent monitoring and dose adjustments. Patient education is important when drugs with a narrow therapeutic index, such as warfarin and low-molecular-weight-heparins (LMWH), are prescribed. Patients who take anticoagulants need to understand the risks and benefits of the medications, the need for regular blood tests, when to contact the physician, when to seek immediate medical attention, the importance of compliance, and the potential for medication interactions. To accomplish these goals, patients are instructed verbally, or with videos, or by use of written information.

    Written communication is efficient and is the least costly method to inform and instruct patients. However, available material is often written at levels beyond the patient’s literacy level.1234 Literacy is defined as the ability to use printed and written information to function in society, to achieve one’s goals, and to develop one’s knowledge and potential.5 A 1992 survey estimated that 21% of the adult population in the United States had only rudimentary reading and writing skills.5 Among elderly patients, the prevalence of inadequate literacy increased with age (15.6% for ages 60 to 65 and 58% for ages >85).6 In the health care setting, health literacy is defined as the ability to perform basic reading and numerical tasks required to function in the health care environment.27 People in the lowest literacy level have difficulty reading and understanding material written at the 6th-grade level. Persons with marginal literacy levels have difficulty reading and understanding material written at the 10th-grade level. Finally, persons with adequate literacy levels comprehend most material written for health care purposes (above 10th-grade level).6

    The impact of literacy on health is significant.2 Adults with low literacy skills have a poorer health status,8 have average health costs that are 6 times higher,9 are less likely to comply with medication regimens, and are less likely to understand their illnesses. For example, patients who have the human immunodeficiency virus and who are at the lowest literacy level are 4 times less likely to adhere to antiretroviral regimens.10 Fewer patients with hypertension who were at the lowest literacy level knew that a blood pressure >160/100 was high (55%, compared with 92% of those with higher literacy levels). Also, fewer patients with diabetes at the lowest reading level knew the symptoms of hypoglycemia (50%, compared with 94% of those with higher literacy levels).7 Clinicians need to be sensitive to the fact that low literacy, or associated factors, may impact clinical interventions, compliance, or outcomes.

    Elderly patients are at a greater risk for not following directions because of lower literacy levels, greater numbers of prescriptions, more prevalent cognitive impairment, and higher rates of stroke. Therefore, appropriate low literacy educational material for patients is necessary. Whether teaching material for patients on anticoagulants is written at a low reading level or not is unknown. Our objective was to determine the readability of patient information material offered to patients receiving anticoagulants.

    Subjects and Methods

    We obtained printed patient information regarding the use of anticoagulants from manufacturers of warfarin and LMWH, health advocacy groups (American Heart Association, National Stroke Association), the United States Pharmacopoeia, and others. We also obtained information posted on the Internet. Anticoagulation management units commonly use patient information reviewed in this report. We excluded information written in languages other than English and information written specifically for health care professionals.

    Readability of written information was measured using the SMOG grade formula11 (SMOG is not an acronym). We chose the SMOG formula because it is accurate and correlates highly with other readability formulas (FOG, 0.99; Fry, 0.93).12 The SMOG, recommended by the American Cancer Society,13 is simple, easy to use,1214 and is widely used in health literacy studies.151617 Briefly, the method consists of first selecting 3 groups of 10 consecutive sentences at the beginning, middle, and end of the document, for a total of 30 sentences. Then, all words with 3 or more syllables within those sentences are tallied and added together. Next, the square root of that total is obtained and its integer calculated. The number 3 is added to the integer to obtain the grade level of the document.11 A modified formula was used to assess the grade level for brochures with <30 sentences.18 The test-retest reliability among 15 randomly selected brochures showed a grade level difference of 0.2 (SD 1.4); 73.3% of grades were the same or were within 1 grade level.

    The Flesch-Kincaid Grade Level formula was also used to determine readability. The Flesch-Kincaid is appealing because of its availability in commercial word processing software (Microsoft Word 7.0, Microsoft Corp). The formula utilized in the software is [(0.39×ASL)+(11.8×ASW)−15.59], where ASL is the average sentence length (number of words divided by number of sentences) and ASW is the average syllables per word (number of syllables divided by number of words).19

    We used ANOVA to compare means and the Pearson correlation coefficient to assess the relationship between the 2 methods of determining readability. The level of significance was set at P<0.05.


    We examined 50 brochures: 8 (16%) dealing with atrial fibrillation, 22 (44%) concerning the use of warfarin, 6 (12%) discussing the use of LMWH, and 14 (28%) related to other themes (Tables 1 through 4). Eighteen brochures (36%) were produced by health advocacy groups and 32 (64%) by private industry. We found 9 brochures (18%) on the Internet. Eighteen brochures (36%) contained fewer than 30 sentences.

    The mean SMOG readability grade level was 10.7 (95% CI 10.1 to 11.2); 12% of the brochures had readability scores at the 7th- to 8th-grade levels, 74% at the 9th- to 12th-grade levels and 14% at higher than 12th-grade level (Table 5). The SMOG readability grade level was similar for brochures produced by health advocacy groups (10.7 grade) and private industry (10.6 grade; P=0.9). Readability levels were higher for information obtained from the Internet (12.2±1.3 grades) compared with other patient information materials (10.3±2.1 grades; P=0.01).

    The readability level was the same for brochures containing >30 sentences compared with shorter brochures (P=0.9). The readability grade was similar for brochures related to atrial fibrillation (10.6 grade), to the use of warfarin (10.9 grade), to the use of LMWH (10.4 grade), or to other themes (10.4 grade; P=0.8).

    For the same brochures, the Flesch-Kincaid mean readability grade was 8.8 (95% CI 8.3 to 9.4; Table 5). The mean grade level as determined by the Flesch-Kincaid formula was 1.8 lower than the SMOG grade level (95% CI 1.4 to 2.3). The correlation between the Flesch-Kincaid and the SMOG was 0.69 (P<0.001).


    We found that most written patient information material (88%) regarding the use of anticoagulants is written at the 9th-grade educational level or higher. We used an accepted method to determine document readability, the SMOG grade level.121314 Similar findings have been shown in other areas of medicine. Patient information was written at the 8th- to 10th-grade levels or beyond in brochures regarding smoking cessation,14 asthma,20 diabetes,21 cancer,13 and informed consent.22 The high readability levels did not differ among shorter and longer brochures, according to the theme discussed, or with regard to the source of the information. As expected, patient information material available on the Internet had higher readability levels.

    The readability level of patient information material contrasts with the observed patients’ abilities to read. One third to one half of English speaking patients have difficulty reading material at the 10th-grade level.623 The estimates are greater among older patients at urban public hospitals (81%)7 and among Spanish-speaking patients (54% to 83%).67 Another compounding problem is that a patient’s educational level does not automatically guarantee proficiency at that same level. Patients’ observed reading abilities are usually 3 to 5 grade levels below what they report as grade completed. For example, among patients receiving warfarin at an anticoagulation management unit, 53% could not read material written at the 9th-grade level, while 83% of them reported having completed the 9th grade or beyond.24 Tailoring readability of patient information to reported grade completed may result in inappropriate material.

    The Flesch-Kincaid formula may seem an attractive method to determine readability, because it is available in commercial word processing software. However, it provides lower estimates of readability. In other studies, the Flesch-Kincaid formula yielded estimates of 0.9 to 3.2 grades lower than standard readability formulas.325 We recommend that the Flesch-Kincaid formula not be used to determine readability of printed information.

    Patients taking anticoagulants who are at risk for bleeding and thrombosis need to learn and understand their condition. As increasing numbers elderly patients with atrial fibrillation receive warfarin, the need for more efficient and effective ways to communicate with them will increase. Patient information should be written at an appropriate reading level, and its readability could be determined by using the SMOG formula. The National Work Group on Literacy and Health recommends that material be written at or below the 6th-grade level,126 because material written at higher levels is less likely to be read or understood. Developing patient information at a low readability level is necessary but not sufficient to improve comprehension. Other methods of communication, and written information that uses figures, pictograms, large font, and other characteristics, may also improve comprehension.27 Future directions should include the development and testing of patient information materials written at a low reading level.

    In summary, patient information material regarding the use of anticoagulants is written at levels beyond the comprehension of most patients. The individual readability levels displayed in Tables 1 through 4 could be used when determining the most appropriate materials for patients, but none meet the recommendation for 6th-grade level or below.

    Appendix A1

    Sources of Patient Education Material †United States Pharmacopeial Convention, Inc. Complete Drug Reference: United States Pharmacopeia. Yonkers, NY: Consumer Reports Books; 1998.

    Table 1. Brochure Readability, Atrial Fibrillation (n=8)

    Brochure NameSource (See Appendix)SMOG Grade LevelFlesch-Kincaid Grade Level
    Atrial Fibrillation1Mosby, Inc.88.3
    What is Arrhythmia?American Heart Association97.2
    Detecting Atrial Fibrillation for Stroke PreventionNational Stroke Association96.5
    Atrial Fibriwhat?DuPont Pharma106.9
    Atrial Fibrillation, Coumadin® and YouDuPont Pharma117.8
    Atrial Fibrillation: Management of This Irregular Heartbeat2Mayo Clinic1210.2
    Atrial Fibrillation23M Pharmaceuticals1310.7
    Anticoagulant Information2American Heart Association1311

    1Brochure contains <30 sentences.

    2Brochure posted on the Internet.

    Table 2. Brochure Readability, Warfarin (n=22)

    Brochure NameSource (See Appendix)SMOG Grade LevelFlesch-Kincaid Grade Level
    Your Heart and AnticoagulantsAmerican Heart Association74.4
    Caregiver Guide to Coumadin® Therapy1DuPont Pharma88.4
    Coumadin® Educational Assessment Form1DuPont Pharma810
    Dosage Calendar1DuPont Pharma88.4
    Patient InstructionsApothecon8.56.1
    Warfarin Sodium: Treating With CareApothecon8.55.6
    Your Daily Medical Diary1Apothecon94.4
    Your Medication Has Been Changed to Warfarin Sodium1Apothecon98.6
    A Patient’s Guide to Using Coumadin®DuPont Pharma107
    Maintaining the Delicate Balance1DuPont Pharma1110
    Coumarin Anticoagulants2Healthanswers, Inc118.6
    Maximizing Coumadin®Prevention Magazine118.8
    Anticoagulants2United States Pharmacopaeia119.6
    Anticoagulants—SystemicUnited States Pharmacopaeia119.8
    Warfarin Sodium TabletsBarr Laboratory11.58.8
    Caregiver’s Guide to Coumadin® Therapy1DuPont Pharma1210.3
    Important Facts About Your Coumadin® (Warfarin Sodium) Therapy1DuPont Pharma128.1
    Warfarin Sodium12Mosby129.4
    If It Doesn’t Say Coumadin®, It Isn’t1DuPont Pharma1410.9
    INR—Q & ADuPont Pharma14.512
    Balancing Your Anticoagulant2Mayo Clinic1511.8
    A Patient’s Guide to Vitamin K1DuPont Pharma1812

    1Brochure contains <30 sentences.

    2Brochure posted on the Internet.

    Table 3. Brochure Readability, Low-Molecular-Weight-Heparin (n=6)

    Brochure NameSource (See Appendix)SMOG Grade LevelFlesch-Kincaid Grade Level
    Helping Recovery—At Home Review1Rhone-Poulenc Rorer912
    Administration of Fragmin® Injection1Pharmacia & Upjohn109.6
    Helping Recovery—At HomeRhone-Poulenc Rorer10.58.6
    Dalteparin—SystemicUnited States Pharmacopaeia118.5
    Enoxaparin—SystemicUnited States Pharmacopaeia119.6
    Heparin—SystemicUnited States Pharmacopaeia118.2

    1Brochure contains <30 sentences.

    2Brochure posted on the Internet.

    Table 4. Brochure Readability, Other (n=14)

    Brochure NameSource (See Appendix)SMOG Grade LevelFlesch-Kincaid Grade Level
    Stroke1Mosby, Inc88.7
    Heart Attack and Stroke: Signals and ActionAmerican Heart Association96.8
    Deep Vein Thrombosis and Pulmonary EmbolismDuPont Pharma95.6
    Deep Vein Thrombosis1Mosby, Inc99.3
    Congestive Heart Failure: What You Should KnowAmerican Heart Association108.2
    Heart Valve SurgeryAmerican Heart Association107.9
    How Stroke Affects BehaviorAmerican Heart Association107.5
    Strokes: A Guide for the FamilyAmerican Heart Association108.8
    Valvular Heart DiseaseDuPont Pharma108.3
    Pulmonary Embolism—What You Know May Save Your Life2Mayo Clinic11.59.6
    Stroke—Your Guide to Prevention and Recovery2Mayo Clinic11.59.3
    What You Should Know About StrokeAmerican Heart Association129.3
    Recurrent Stroke1National Stroke Association1212
    Stroke Is A Brain AttackNational Stroke Association1311.6

    1Brochure contains <30 sentences.

    2Brochure posted on the Internet.

    Table 5. Brochure Readability, Summary

    SMOG Grade Level (n=50)Flesch-Kincaid Grade Level (n=50)
    Grade level, mean (95% CI)10.7 (10.1–11.2)8.8 (8.3–9.4)
    Grade level, n (%)
    4th–6th grade05 (10%)
    7th–8th grade6 (12%)15 (30%)
    9th–12th grade37 (74%)30 (60%)
    >12th grade7 (14%)0

    Table A1. Sources of Patient Education Material

    Organizations/CompaniesTelephone NumbersLocation in Table
    American Heart Association1-800-242-17931, 2, 4
    Barr Laboratory1-888-927-32742
    DuPont Pharma1-800-441-75151, 2, 4
    Mosby*1-800-426-45451, 4
    National Stroke Association1-800-787-65371, 4
    Pharmacia & Upjohn1-888-768-55013
    Prevention Magazine1-800-666-25032
    Rhone-Poulenc Rorer (now Aventis Pharmaceuticals)1-800-340-75023
    United States Pharmacopeia†1-800-227-87722, 3
    Internet SitesURL AddressesLocation in Table
    American Heart Association (accessed 3/5/99)
    3M Pharmaceuticals (accessed 3/1/99)
    Healthanswers, Inc. (accessed 4/21/99)
    Mayo Clinic (accessed 4/21/99), 2, 4
    Mosby, Inc (accessed 4/21/99)
    United States Pharmacopeia (accessed 4/21/99),13359.asp2

    *Moore SW. Griffith’s Instructions for Patients. 6th ed. Philadelphia, Pa: WB Saunders: 1998.

    This study was funded in part by grant NR 04716 from the National Institute of Aging, National Institute of Nursing Research, and Office of Research on Minority Health from the Center on Minority Aging, University of North Carolina at Chapel Hill; and a Faculty Development Grant from the Brody School of Medicine at East Carolina University. We thank Laurin Gibson for assisting in the design of the study and Amy Jackson for administrative support. We also thank Sylvia English, George Ho, Brian Peek, Wilhelmine Wiese, and Glyn Young for reviewing prior versions of this manuscript.


    Correspondence to Dr Carlos Estrada, Brody School of Medicine at East Carolina University, 600 Moye Boulevard, PCMH TA-389, Greenville, NC 27858-4353. E-mail


    • 1 The National Work Group on Literacy and Health. Communicating with patients who have limited literacy skills. J Fam Pract.1998; 46:168–176.MedlineGoogle Scholar
    • 2 Ad Hoc Committee on Health Literacy for the Council on Scientific Affairs, American Medical Association. Health literacy: report of the Council on Scientific Affairs. JAMA.1999; 281:552–557.CrossrefMedlineGoogle Scholar
    • 3 Feldman SR, Quinlivan A, Williford P, Bahnson JL, Fleischer AB Jr. Illiteracy and the readability of patient education materials: a look at Health Watch. N C Med J.1994; 55:290–292.MedlineGoogle Scholar
    • 4 Davis TC, Crouch MA, Wills G, Miller S, Abdehou DM. The gap between patient reading comprehension and the readability of patient education materials. J Fam Pract.1990; 31:533–538.MedlineGoogle Scholar
    • 5 National Adult Literacy Survey. National Center for Education Statistics Web site. 1992. Available at: Accessed March 30, 1998.Google Scholar
    • 6 Gazmararian JA, Baker DW, Williams MV, Parker RM, Scott TL, Green DC, Fehrenbach SN, Ren J, Koplan JP. Health literacy among medicare enrollees in a managed care organization. JAMA.1999; 281:545–551.CrossrefMedlineGoogle Scholar
    • 7 Williams MV, Parker RM, Baker DW, Parikh NS, Pitkin K, Coates WC, Nurss JR. Inadequate functional health literacy among patients at two public hospitals. JAMA.1995; 274:1677–1682.CrossrefMedlineGoogle Scholar
    • 8 Weiss BD, Hart G, McGee DL, D’Estelle S. Health status of illiterate adults: relation between literacy and health status among persons with low literacy skills. J Am Board Fam Pract.1992; 5:257–264.MedlineGoogle Scholar
    • 9 Weiss BD, Blanchard JS, McGee DL, Hart G, Warren B, Burgoon M, Smith KJ. Illiteracy among Medicaid recipients and its relationship to health care costs. J Health Care Poor Underserved.1994; 5:99–111.CrossrefMedlineGoogle Scholar
    • 10 Kalichman SC, Ramachandran B, Catz S. Adherence to combination antiretroviral therapies in HIV patients of low health literacy. J Gen Intern Med.1999; 14:267–273.CrossrefMedlineGoogle Scholar
    • 11 McLaughlin GH. SMOG grading: a new readability formula. J Reading. 1969;639–646.Google Scholar
    • 12 Meade CD, Smith CF. Readability formulas: cautions and criteria. Patient Educ Couns.1991; 17:153–158.CrossrefGoogle Scholar
    • 13 Meade CD, Diekmann J, Thornhill DG. Readability of American Cancer Society patient education literature. Oncol Nurs Forum.1992; 19:51–55.MedlineGoogle Scholar
    • 14 Meade CD, Byrd JC. Patient literacy and the readability of smoking education literature. Am J Public Health.1989; 79:204–206.CrossrefMedlineGoogle Scholar
    • 15 Meade CD, Howser DM. Consent forms: how to determine and improve their readability. Oncol Nurs Forum.1992; 19:1523–1528.MedlineGoogle Scholar
    • 16 Merritt SL, Gates MA, Skiba K. Readability levels of selected hypercholesterolemia patient education literature. Heart Lung.1993; 22:415–420.MedlineGoogle Scholar
    • 17 Overland JE, Hoskins PL, McGill MJ, Yue DK. Low literacy: a problem in diabetes education. Diabetes Med.1993; 10:847–850.CrossrefMedlineGoogle Scholar
    • 18 Weinrich SP, Boyd MD, Powe BD. Tool adaptation for socioeconomically disadvantaged populations. In: Frank-Stromborg M, Olsen SJ. Instruments for Clinical Health-Care Research. 2nd ed. Sudbury, Mass: Jones and Bartlett; 1997:20–30.Google Scholar
    • 19 Microsoft Corporation. WD97: Frequently asked questions about the grammar checker [Web site]. October 1999. Available at: Scholar
    • 20 Smith H, Gooding S, Brown R, Frew A. Evaluation of readability and accuracy of information leaflets in general practice for patients with asthma. BMJ.1998; 317:264–265.CrossrefMedlineGoogle Scholar
    • 21 Albright J, de Guzman C, Acebo P, Paiva D, Faulkner M, Swanson J. Readability of patient education materials: implications for clinical practice. Appl Nurs Res.1996; 9:139–143.CrossrefMedlineGoogle Scholar
    • 22 Hopper KD, TenHave TR, Tully DA, Hall TE. The readability of currently used surgical/procedure consent forms in the United States. Surgery.1998; 123:496–503.CrossrefMedlineGoogle Scholar
    • 23 Williams MV, Baker DW, Parker RM, Nurss JR. Relationship of functional health literacy to patients’ knowledge of their chronic disease: a study of patients with hypertension and diabetes. Arch Intern Med.1998; 158:166–172.CrossrefMedlineGoogle Scholar
    • 24 Estrada CA, Barnes V, Hryniewicz MM, Collins C, Byrd JC. Low literacy and numeracy are prevalent among patients taking warfarin. J Gen Intern Med.1999; 14:27. Abstract.CrossrefMedlineGoogle Scholar
    • 25 Mailloux SL, Johnson ME, Fisher DG, Pettibone TJ. How reliable is computerized assessment of readability? Comput Nurs.1995; 13:221–225.MedlineGoogle Scholar
    • 26 Weiss BD, Coyne C. Communicating with patients who cannot read. N Engl J Med.1997; 337:272–274.CrossrefMedlineGoogle Scholar
    • 27 Doak CC, Doak LG, Root J. Teaching Patients With Low Literacy Skills. 2nd ed. Philadelphia, Pa: JB Lippincott; 1996.Google Scholar