Assessing reading levels of health information: uses and limitations of flesch formula

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Date: January-April 2017
From: Education for Health(Vol. 30, Issue 1)
Publisher: Medknow Publications and Media Pvt. Ltd.
Document Type: Report
Length: 3,367 words
Lexile Measure: 1810L

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Byline: Pranay. Jindal, Joy. MacDermid

Background: Written health information is commonly used by health-care professionals (HCPs) to inform and assess patients in clinical practice. With growing self-management of many health conditions and increased information seeking behavior among patients, there is a greater stress on HCPs and researchers to develop and implement readable and understandable health information. Readability formulas such as Flesch Reading Ease (FRE) and Flesch–Kincaid Reading Grade Level (FKRGL) are commonly used by researchers and HCPs to assess if health information is reading grade appropriate for patients. Purpose: In this article, we critically analyze the role and credibility of Flesch formula in assessing the reading level of written health information. Discussion: FRE and FKRGL assign a grade level by measuring semantic and syntactic difficulty. They serve as a simple tool that provides some information about the potential literacy difficulty of written health information. However, health information documents often involve complex medical words and may incorporate pictures and tables to improve the legibility. In their assessments, FRE and FKRGL do not take into account (1) document factors (layout, pictures and charts, color, font, spacing, legibility, and grammar), (2) person factors (education level, comprehension, health literacy, motivation, prior knowledge, information needs, anxiety levels), and (3) style of writing (cultural sensitivity, comprehensiveness, and appropriateness), and thus, inadequately assess reading level. New readability measures incorporate pictures and use complex algorithms to assess reading level but are only moderately used in health-care research and not in clinical practice. Future research needs to develop generic and disease-specific readability measures to evaluate comprehension of a written document based on individuals' literacy levels, cultural background, and knowledge of disease.


Patient education is an integral part of clinical practice. Allied health-care professionals (HCPs), physicians, and nurses commonly use written medical information materials for patient education. Many patients use the Internet for reading information about their health conditions and their treatment. The advantages of interactivity and anonymity [sup][1] have made the Internet a prominent source of health information for both professionals and general public.[sup][2],[3] The Internet has increased the volume of available text health information and consumers have increasingly gone online to search medical information.[sup][2],[4],[5],[6],[7] Many health-care interventions, such as diabetes management, smoking cessation, and back pain rehabilitation, are now being delivered online for a variety of perceived benefits.[sup][8] With the increasing push for self-management and home programs for many health conditions, there is a need for health information materials which can be easily read and understood by patients. However, there is a lack of evidence-based health information which can be accessed, read, and understood by the general public.[sup][9]

Written health material is predominantly used in patient education and online health information. It is important for a patient to be able to read and understand the information for better engagement in his healthcare. Patient engagement is essential for meaningful health outcomes and to enhance patient satisfaction.[sup][10] Researchers and clinicians also use written health information to assess patient recovery, satisfaction with care, and areas of improvement in services. Readability formulas are commonly used to evaluate the reading level of written health information which might include test protocols and instructions, home exercise and care instructions, information pamphlets, consent and assent forms, patient-reported outcome measures, and surveys. Easy to read and understand written document allows accurate reporting, active research participation, and enhanced clinical practice.

Despite increased use of the Internet by people and improved availability of online health information, many of these resources remain underutilized as they cannot be read and understood by common people.[sup][11],[12],[13],[14] In the field of health-care research, many informed consent and patient reported outcome measures are above the level of reading ability of a common man [sup][15],[16] which might yield inaccurate results. Readability is defined as “the sum total (including all the interactions) of all those elements within a given piece of printed material that affect the success a group of readers have with it. The success is the extent to which they understand it, read it at an optimal speed, and find it interesting.”[sup][17]

Many readability formulas such as Flesch, Dale–Chall, and Gunning Fog Index exist for checking the readability of a text in English.[sup][18] A few readability formulas are also available for checking the readability of non-English text, for example, READ-IT [sup][19] (Italian), Spaulding, modified Fry graph, and Crawford formula [sup][20] (Spanish), and Lix Readability Formula [sup][21] (Swedish). Most reading formulas give scores by doing mathematical calculations based on the number of words per se ntence, mean word length, and number of syllables per word.[sup][22] Due to the complexity involved in assessing reading ease, many researchers and health-care providers use multiple readability measures to more accurately evaluate the readability of a given written document.[sup][23] The Flesch formula is most commonly used to assess the readability of written health-care information materials.[sup][18],[24],[25],[26] In this article, we will critically analyze the credibility and role of Flesch formula in assessing the readability of written health information.

The Flesch formula

Rudolph Flesch developed the Flesch Reading Ease (FRE) formula in 1948. Flesch Reading Grade Level (FRGL) formula was built upon in FRE by Kincaid et al. in 197 5 for the US Navy to give a grade level to written material.[sup][25] It is commonly referred as Flesch–Kincaid Reading Grade Level (FKRGL). Both FRE and FKRGL calculate the readability based on two variables: average sentence length (based on the number of words) and average word length (based on the number of syllables).

The validity of Flesch Reading Ease and Flesch–Kincaid Reading Grade Level

Both the FRE formula and FKRGL are valid for measuring the readability of a written text between US Grade 5 and college level.[sup][24],[25] The FRE scores have been validated against 1950 McCall-Crabbs Standard Test in reading lessons,[sup][27] and FRE scores correlate 0.6 with 1950 McCall-Crabbs Standard Test.[sup][28] The FRE scores also correlate highly with Fry (0.96) and Simple Measure of Gobbledygook (0.95) readability formulas.[sup][29] Since comprehension is an important aspect to understand the written findings, the FKRGL has also been validated against the cloze comprehension tests.[sup][25],[30] Since FKRGL is validated against the cloze comprehension tests and they directly give a grade level (as opposed to an estimate in FRE), FKRGL is more commonly used in daily practice.[sup][26]


Both FRE and FKRGL can be calculated manually and electronically. The score derived from FRE ranges from 0 (unreadable) to 100 (very easy to read). FKRGL also gives a score that corresponds to the US grade level. For example, a FKRGL of 8.5 means that the text should be understood by people achieved US Grade 8. To reach people with low levels of literacy, it is suggested that written health-care information materials are to be targeted at Grade level 8 or less in the US [sup][31],[32] and Grade level 12 in the UK.[sup][31] Interpretations of FRE scores [sup][28] and estimated grade level are in [Table 1].{Table 1}

Advantages and limitations

As both FRE and FKRGL are readily available within the MS Office suite, they are the most preferred readability formulas.[sup][33] FRE and FKRGL exclude subtitles, captions, and headings.[sup][34] Furthermore, the FRE and FKRGL scores cannot be calculated on tables, charts, and graphics.[sup][35] MS Word recognizes each period as the end of a sentence. Thus, abbreviations, numbers with decimals, and bullet headings might reduce the reading level thus underestimating the grade level.[sup][34]

Critical analysis

To understand written health-care information, patients need to go beyond reading and actually comprehend the information. Comprehension depends on various factors such as (a) text layout (title, font, colors, tables, graphics, spacing, and grammar),[sup][31],[36] (b) patient motivation and prior knowledge of the subject which helps them to derive meaning from the written text,[sup][37] and (c) patient anxiety levels.[sup][38] FRE and FKRGL do not take prior knowledge, motivation, layout, grammar, and graphics into consideration; and rely only on word and sentence length.[sup][34],[39]

Despite common use of FRE and FKRGL, its validation and scoring algorithm are still debated. Some authors suggest that there has been an inadequate validation of the FRE and FKRGL.[sup][40] It is noteworthy that McCall-Crabbs Standard Test was never intended to be used as a criterion for reading formula.[sup][40] Both medical and lay terminologies and vocabulary have changed greatly over the past 60 years, and 1950 standards of McCall-Crabbs test are outdated now.[sup][27] Importantly, passages used while developing McCall-Crabbs test for comprehension were too short and simple [sup][40] and do not have the necessary capacity to accurately assess the reading level of a document consisting of complex medical words. Due to the built-in availability within MS Office, the FRE and FKRGL have become a readily available option but provide lower estimates of readability as compared to other reading formulas.[sup][41]

FRE and FKRGL scores are based on word or sentence length, thus including a complex medical word might increase the reading level of the document. However, patients with chronic health conditions may be familiar with the medical terms relating to their health condition. Using a simpler or uncommon word may decrease the grade level but might fail to capture the interest of patients, might undermine their confidence in its credibility, or might not provide the needed in-depth information.[sup][39],[42] Furthermore, in a health information document, keywords are often repeated to reinforce learning, which will lead to inappropriately higher FRE and FKRGL scores for these texts.

Current options for readability formulae

Since the use of graphics influence readability, new readability measures such as Readability Assessment Instrument,[sup][43] Ensuring Quality Information for Patients,[sup][44] and Suitability Assessment of Materials [sup][45] have been developed in the past decade to assess the effectiveness of diagrams and pictures with text. These measures can be used by health-care providers in conjunction with FRE and FKRGL to develop effective patient education materials. Often home programs and outcomes' measures use a combination of text, tables, and figures; these alternative readability measures may be more valid.

Researchers and clinicians can assess patient literacy and later combine readability formula findings with literacy assessment to develop audience-appropriate education materials. Patient literacy assessment tools such as Rapid Estimate of Adult Literacy in Medicine,[sup][46] Test of Functional Health Literacy in Adults,[sup][47] Brief Questions to Identify Patients With Inadequate health literacy,[sup][48] Newest Vital Sign,[sup][49] Health Activity Literacy Study,[sup][50] and Wide Range Achievement Test-Revised [sup][51],[52] can be used by clinicians and researchers to assess literacy levels of patients.

Recent scientific developments using computer linguistics have targeted the problems of outdated vocabulary and multiple meanings of the same word faced by FRE and FKRGL. New tools such as ATOS readability formula,[sup][53],[54] Pearson Reading Maturity Metric,[sup][55] the Coh-Metrix Text Easability Assessor,[sup][56] and TextEvaluator [sup][57] are online tools that constantly update their word vocabulary. These tools also use complex algorithms and measure semantic, structural, and vocabulary aspects to provide an accurate assessment of reading levels. These new tools have been used widely in classrooms by teachers to assess the reading level of books and passages in English; however, utilization and utility in health research are subject to further research.


Assessment of reading grade level of written documents is a complex issue. It is influenced by factors related to the document (layout, color, font, spacing, legibility, and grammar); person (education, comprehension, health literacy, motivation, prior knowledge, information needs, anxiety levels); and style of writing (cultural sensitivity, context, comprehensiveness, and appropriateness). Reading formulas are inadequate objective measures but are being used as quick indicators to assist writers in targeting information to the lay public. Sole reliance on FRE and FKRGL or other reading formulas to assess the grade level can be misleading. It is important for HCPs and researchers to move beyond assessing reading grade level–simply can the patient read the document – toward assessing patient's understanding of the document. Assessing understanding is a complex process and is influenced by many intertwined variables. To develop a written document that is engaging to the reader, focuses on the key information, and is technically correct requires consideration of multiple factors related to the document, the target audience, and the information being provided.

Future directions

Multiple reading formulas exist; however, there is a lack of culturally sensitive, disease specific, and context-based readability measures. Future research should focus on developing generic and disease-specific online readability measures that can assess the comprehension of a written document based on individuals' literacy levels, cultural background, cognitive ability, vocabulary, and knowledge of the disease. Future readability measures should also be able to assess reading level of a document containing pictures and charts. Developing and using a measure that is customized to literacy levels, cultural background, and the disease knowledge might also help solve the ongoing problem of health-care information being written in a grade level higher than recommended level.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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Gale Document Number: GALE|A498891108