Mononita Roy , MD, FRCPC 1, 2 , Frank Molnar , MSc, MDCM, FRCPC 1–6
1 Division of Geriatric Medicine, The University of Ottawa, Ottawa, ON;
2 The Ottawa Hospital, Ottawa, ON;
3 The Bruyere Research Institute, Ottawa, ON;
4 The Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, ON;
5 The Regional Geriatric Program of Eastern Ontario, The Ottawa Hospital, Ottawa, ON;
6 CanDRIVE: a CIHR Institute of Aging funded New Emerging Team, Ottawa Hospital Research Institute, Ottawa, ONDOI: http://dx.doi.org/10.5770/cgj.16.76
Background
Fitness-to-drive guidelines recommend employing the Trail Making B Test (a.k.a. Trails B), but do not provide guidance regarding cut-off scores. There is ongoing debate regarding the optimal cut-off score on the Trails B test.
The objective of this study was to address this controversy by systematically reviewing the evidence for specific Trails B cut-off scores (e.g., cut-offs in both time to completion and number of errors) with respect to fitness-to-drive.
Methods
Systematic review of all prospective cohort, retrospective cohort, case-control, correlation, and cross-sectional studies reporting the ability of the Trails B to predict driving safety that were published in English-language, peer-reviewed journals.
Results
Forty-seven articles were reviewed. None of the articles justified sample sizes via formal calculations. Cut-off scores reported based on research include: 90 seconds, 133 seconds, 147 seconds, 180 seconds, and < 3 errors.
Conclusions
There is support for the previously published Trails B cut-offs of 3 minutes or 3 errors (the ‘3 or 3 rule’). Major methodological limitations of this body of research were uncovered including (1) lack of justification of sample size leaving studies open to Type II error (i.e., false negative findings), and (2) excessive focus on associations rather than clinically useful cut-off scores.
Key words: Trail Making Test , Trails B , driving , fitness-to-drive , cut-off
Physicians in most Canadian jurisdictions are legally mandated to report medical findings that could impact on fitness-to-drive (http://www.cma.ca/driversguide).(1) Even where reporting is not mandatory, physicians can still potentially be found liable if they fail to report a patient who harms others due to a car crash attributed to their medical impairments.(2) On a more positive note, the reporting of medical findings that could impact on fitness-to-drive also represents an opportunity to fulfill an important societal role; assessments of fitness-to-drive allow physicians to help their patients avoid disabling injury or death and also to help patients and their families avoid the grief and legal repercussions associated with contributing to the injuries or deaths of other road users or bystanders.(2)
Driving guidelines such as those of the Canadian Medical Association, the Canadian Council of Motor Transport Administrators, the Driver and Vehicle Licensing Agency in the United Kingdom, and the American Medical Association recommend the Trail Making B Test (a.k.a. Trails B) to assess fitness-to-drive.(1,3,4,5) Trails B tests dual attention (cognitive flexibility in switching attention between two competing static sets of stimuli which is a much lower level of cognitive demand than switching between multiple moving stimuli encountered when driving) and executive function. Driving represents a “super-Instrumental Activity of Daily Living (super-IADL)” or “super-executive function” that can result in death if performed incorrectly or too slowly—this, along with the risk to others, makes it unique among IADLs or executive functions. Unfortunately, guidelines rarely advise physicians regarding which Trails B findings indicate unfitness-to-drive.
A study by Tombaugh(6) of the normative values of the Trails B test demonstrated that the mean time to complete Trails B is < 180 seconds for all age groups. There were some outliers whose scores exceeded 180 seconds; the lowest 20th percentile in the 80 to 84 age group and the lowest 30th percentile in the 85 to 89 age group, but the validity of the latter findings is questionable given the small sample size in these age-specific cells. It is also possible that some of these findings do not represent true normative values (i.e., values for persons without diseases or drugs affecting the results), but may represent hidden disease or hidden medication effects.(7) Even if these are true norms for healthy people, being in a normative range may not necessarily mean the patient is safe to drive. We have to accept reality—as people get older, they do not have more time to stop their cars or to respond to emergencies. Physical laws do not change according to age. We must, therefore, remain very skeptical of age-adjusted norms for tests used to screen for fitness-to-drive.(7)
Continuing medical education articles have recommended a Trails B cut-off of 180 seconds or three errors (i.e., 3 minutes or 3 errors; the ‘3 or 3 rule’).(2,7,8) Given the findings of Tombaugh,(6) indicating the scores of the lowest 20th percentile in the 80 to 84 year-old group and the lowest 30th percentile in the 85 to 89 year-old group exceeded 180 seconds, some have recommended caution in employing a strict 180 second cut-off. There is ongoing debate in the field of research into the evaluation of fitness-to-drive regarding the optimal cut-off score on the Trails B test.
The objective of this study was to address this controversy by systematically reviewing the evidence for specific Trails B cut-off scores (e.g., cut-offs in both time to completion and number of errors) with respect to fitness-to-drive.
This systematic review was conducted in accordance with the process and methods recommended by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.(9)
The need for ethics approval was waived for this study by the Ottawa Hospital Research Ethics Board, as it only involved a literature search.
An electronic literature search was conducted using CINAHL, Cochrane Database of Systematic Reviews, EMBASE, MEDLINE, PsycINFO, PubMed, and Scopus databases for all relevant English-language publications. No starting date restriction was used in this search. The most updated search was conducted in November 2012. Relevant articles were retrieved using the following subject headings and keywords in various combinations: Trail Making Test, Trail Making Test B, Trail Making B, Trail Making Test Part B, Trail Making Test A and B, Trail Making Test Parts A & B, Trail Making Test Parts A and B, Trails B, TMT, TMT-B, drive/driving/driver, auto/automobile, car, vehicle/motor vehicle, accident, traffic, crash, collision, MVA and MVC. This electronic search was supplemented by hand searching of the reference lists of selected articles, meta-analyses, and review articles.
All prospective cohort, retrospective cohort, case-control, correlation, and cross-sectional studies reporting the ability of the Trails B test (i.e., the standard Arabic numerals version employing numbers 1–13 and letters A–L) to predict driving safety were included.
The systematic review was restricted to articles presenting original research findings published in English-language, peer-reviewed journals. Reviews, meta-analyses, commentaries, editorials, consensus statements, and guidelines were searched for references, but were not included in the systematic review.
Data extraction forms included publication details, investigative site locations, source of participants, design type, sample size, whether power and sample size calculations were provided, age of participants, diseases included (e.g., Alzheimer’s Disease, Parkinson’s Disease, stroke, traumatic or anoxic brain injury etc.), method of evaluating driving safety (e.g., simulator, on-road, questionnaire, record of crashes), reported associations of Trails B with predicting driving safety, whether a cut-off was reported for Trails B, and source of reported cut-off (study analysis or reference).
Two investigators (MR, FM) independently extracted data from all included studies, and then met to identify and discuss discrepancies in extracted data. Disagreements between the reviewers were discussed and a consensus agreement was reached.
Since Trails B is not routinely employed as part of a multivariate equation in clinical practice, we focused on univariate associations (i.e., the score of the Trails B in isolation, not as part of a multivariate equation).
Figure 1 illustrates the process of selection of articles for the systematic review. After reviewing 97 articles in detail, including a hand search of the reference sections, a total of 47 articles met the inclusion criteria to be systematically reviewed. Study characteristics are presented in Table 1. The primary outcome (i.e., measures of driving safety) was history of crash (reported or recorded) for 10 (21.3%) studies, simulator test score for 10 (21.3%) studies, and on-road assessment for 27 (57.4%) studies.
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FIGURE 1. Article selection flow diagram |
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TABLE 1.
Characteristics of included studies
Table 2 shows the associations of Trails B with predicting driving safety (primary outcome), organized according to sample sizes in ascending order. Trails B was positively associated with determining fitness-to-drive in 32 out of 47 (68.1%) studies and found to have no association in 15 (31.9%) studies.
TABLE 2.
Reported associations of Trails B with predicting driving safety (studies with no association shaded in gray)
None of the studies justified sample sizes via formal calculations. The sample sizes of many of the studies were small, with 24 (51.1%) studies having fewer than 100 participants (Table 2). Eleven of these 24 studies with N < 100 did not find an association of Trails B with driving safety. Stated another way, of the 15 studies showing no association (shaded in gray in Table 2), 11 (73.3%) had small sizes of ≤ 100. The remaining four studies with no association had sample sizes of 144, 155, 176, and 1,876.
Table 3 shows the studies that reported cut-off values for Trails B in predicting fitness-to-drive. Eight of the 47 studies (17.0%) reported cut-off values for Trails B from various sources. Five of these studies reported cut-off values derived from analysis of their data (i.e., primary research): 90 seconds,(10) 133 seconds,(11) 147 seconds,(12) 180 seconds,(13) and < 3 errors.(14)
TABLE 3.
Studies reporting Trails B cut-off values
Three studies reported cut-off values from references cited within their papers: 180 seconds (3 minutes)(15,16) and ≥ 292 seconds.(17) Two of these references (Table 3) are not original research,(18,19) and the remaining three references are not driving studies.(6,20,21) The 292 second cut-off was derived from a neuropsychology textbook,(22) not a driving study.
Therefore, in addition to the three continuing medical education articles(2,7,8) recommending a 3 minute or 3 error cut-off (the ‘3 or 3 rule’), this systematic review uncovered four additional articles supporting this cut-off (15,13,16,14) and three other studies recommending even shorter time cut-offs ranging from 90 seconds to 147 seconds.(10, 11, 12)
Some have argued that no in-office tests can determine fitness-to-drive in all situations. This statement is correct, but is often misinterpreted as meaning in-office tests can never be used to determine fitness-to-drive in any situation. While it is obvious that no single in-office tests can be expected to be able to determine fitness-to-drive in all situations, it is a fundamental error in logic to assume therefore that in-office tests cannot determine fitness-to-drive in some situations.
To illustrate the point, as performance on tests such as Trails B progressively worsens with longer completion times and/or more errors, then clinicians should become increasingly comfortable stating a patient “has a potential functional impairment that may increase the risk of crash”. For instance, if a patient took 10 minutes to complete Trails B and made ten errors with no concerns regarding the validity of the test, then most physicians would likely feel justified in sending this information to their Ministry of Transportation as a finding that could impact on fitness-to-drive.
The extreme findings described above represent situations in which physicians can determine fitness-to-drive using in-office tests. Situations in which deficits are less glaring are more challenging. One way to address more borderline situations is for physicians to carefully consider precisely what they are being asked to evaluate. In Ontario, Canada, the Highway Traffic Act requires the following:
203. (1) Every legally qualified medical practitioner shall report to the Registrar the name, address and clinical condition of every person sixteen years of age or over attending upon the medical practitioner for medical services who, in the opinion of the medical practitioner, is suffering from a condition that may make it dangerous for the person to operate a motor vehicle. R.S.O. 1990, c. H.8, s. 203.(1)
In Ontario, physicians are not asked to determine fitness-to-drive (i.e., they are not asked to report patients as fit or unfit to drive), but rather are asked to report findings that may make it dangerous for the person to drive. The Ministry of Transportation retains responsibility for the final determination of fitness-to-drive. When viewed from this perspective, when selecting Trails B cut-offs that may indicate functional impairment that may impact on fitness-to-drive rather than as a final determination of fitness-to-drive, then Trails B cut-offs of 3 minutes or 3 errors (the ‘3 or 3 rule’) remain reasonable to consider when deciding whether or not to bring findings to the attention of the Ministry of Transportation. It is entirely appropriate that the Ministries of Transportation remain responsible for the final determination of fitness-to-drive rather than off-loading their responsibility on MDs.
It is also critical that tests such as Trails B not be misused—they must be accurately interpreted in the context of a number of critical considerations, in order to ensure that they are a valid reflection of function.(1) In order to avoid generating false results, Trails B scores should always be interpreted in the overall clinical context when determining fitness-to-drive.(7) The clinician should confirm that the Trails B results are consistent with the history provided by caregivers and other tests. Low scores must be verified as not to be due to confounding variables such as language barrier, low education, dyslexia, performance anxiety, depression, or sensory deficits, for example.
The administration of Trails B should also be standardized, as cognitive performance can be influenced by many factors. Ideally, all assessors should receive identical instructions on test administration. A practical recommendation may be that assessors receive training through continuing medical education.
For a review of considerations in applying in-office tests to the assessment of fitness-to-drive, please see page 11 of http://www.canadiangeriatrics.ca/default/index.cfm/linkservid/0D194943-EF73-7DAB-77450BB92BFF239A/showMeta/0/.(7) Furthermore, tests such as Trails B can be employed within a more detailed assessment process, as described in http://www.cfp.ca/content/56/11/1123.full.pdf+html?sid=6ddf379a-874a-4d6f-9c64-02c6bf939312.(2)
The evidence from the Tombaugh article(6) (that the mean Trails B score for all age groups is < 3 minutes and only a small number of outliers have Trails B > 3 minutes) and the articles listing fitness-to-drive cut-offs of 3 minutes or 3 errors,(15,13,16,14) support the finding that the best evidence-informed cut-offs we have to date are 3 minutes or 3 errors, as described in three continuing medical education articles.(2,7,8)
In this systematic review, none of the studies justified sample sizes via formal calculations. Eleven of the 15 studies which showed no association between Trails B and driving had small sample sizes of ≤ 100. Due to the risk of type II (beta) errors (i.e., false negative results caused by inadequate sample size or insufficient power), the findings of these 11 small studies cannot be interpreted with any degree of confidence (i.e., we cannot tell if they are true negative or false negative studies). This concern may also be true for the additional three negative studies with sample sizes ranging from 144 to 176.
A limitation of the Trail Making Test is that it requires knowledge of the numbers and letters used in the English language and, thus, may not be appropriate for individuals whose primary language does not employ similar letters and numbers or those who are illiterate. One instrument that has been developed to address this concern is the Color Trails Test (CTT). The CTT is a language-free analogue of the Trails test designed to be applicable across various cultural contexts. Two studies(23,24) (Table 2) looked at the CTT and its association with ability to predict fitness-to-drive. CTT 2 is similar to Trails B. It has two sets of 25 numbers in yellow and pink circles with instructions to connect the numbers in ascending order alternating between the two color sets. Both studies failed to show an association between CTT 2 and driving. However, it should once again be noted that both studies had small sample sizes (N = 29 and 30) and did not show sample size calculations. Therefore, as discussed above, this could have created possible false negative results in both studies.
While the evidence for Trails B cut-offs of 3 minutes or 3 errors (the ‘3 or 3 rule’) is limited, this systematic review reveals that these represent the best evidence-informed cut-offs available to date. It is logical to assume that as the test score worsens (e.g., the time to completion and/or the numbers of errors increase), the person’s fitness-to-drive also worsens (i.e., risk of crash increases). It is, at the very least, reasonable for physicians to consider reporting findings to their Ministry of Transportation if the Trails B score is worse than 3 minutes or 3 errors, provided the test results are felt to be a valid reflection of function.
The body of evidence for Trails B cut-off scores is limited, in part, due to major methodological limitations of driving research uncovered in this study including: (1) lack of justification of sample size making the interpretation of small negative trials impossible as some negative findings may represent Type II or Beta Error (i.e., falsely negative findings due to inadequate sample size/insufficient power); and (2) the fact that most research is focused on associations but often ignores the derivation of cut-off scores, resulting in findings that are not clinically useful.
Not only is more research into Trails B cut-offs needed, but the quality of the research being done (i.e., the methodological standards) must improve. Recommendations for future driving research should therefore include:
The determination of sample size to prevent future small studies from reporting potentially falsely negative findings due to inadequate sample size/insufficient power (Type II or Beta Error). The fact that such sample size calculations are challenging does not justify their exclusion.
The determination of potential clinically useful cut-off scores using Receiver Operating Characteristic (ROC) curve analytic techniques that plot sensitivity vs. 1 - specificity to permit the evaluation of the properties (e.g., sensitivity and specificity) of all potential cut-offs.
Given that there are likely no perfect cut-off scores with perfect sensitivity and specificity, techniques (e.g., Delphi techniques) that balance the risks and benefits of different cut-off scores, derived from ROC analyses, should be incorporated into driving research. Ultimately decisions regarding the best cut-offs need to be based on balancing the risks of missing cases of unsafe drivers vs. the risk of inappropriate loss of driving privileges.
Exploring the use of two cut-off scores to promote Trichotomization—see page 11 of http://www.canadiangeriatrics.ca/default/index.cfm/linkservid/0D194943-EF73-7DAB-77450BB92BFF239A/showMeta/0/(7) and http://onlinelibrary.wiley.com/doi/10.1111/j.1532-5415.2006.00967.x/pdf.(22)
Exploring different scoring methods for Trails B such as Trails (B-A)(25,26,27,28) and Trails B/A.(29) Trails (B-A) has been described as reflecting “the attention and set-switching components of Trails B independent of psychomotor speed”(26) and is often considered the standard index of set-shifting. It is also “a measure of global executive function”.(27) It has been examined in various driving studies with Parkinson’s Disease patients,(25,26,27) and has been found to be a good predictor of driving safety. It is thought that “the flexibility of the cognitive system”, as tested by Trails B-A, “allows drivers to cope with dynamic traffic situations”.(28) Although it is certainly a measure that is worth examining, we chose not to investigate cut-off scores for Trails (B-A) in this systematic review because current guidelines from medical associations recommend the use of Trails B only, not Trails B-A.
Different forms of Trails B that can overcome literacy barriers such as Color Trails.(23,24)
In fact, we do not need to wait to add to this body of evidence. Researchers who have previously published Trails B research (or their MSc and PhD students) can immediately study the following in their existing databases: i) dichotomization via single cut-off scores (both time and number of errors), ii) trichotomization via two cut-off scores (both time and number of errors), and iii) novel scoring methods such as Trails (B – A) and Trails B/A.
The authors declare that no conflicts of interest exist. Neither author has received financial support from private industry for work on the assessment of fitness-to-drive. Both authors were involved in the preparation of this manuscript.
We wish to thank Debbie Ayotte, librarian, for her extensive assistance with literature searches.
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Canadian Geriatrics Journal , Vol. 16 , No. 3 , September 2013