Taken as a whole, the findings of this review suggest that professional interpreters are associated with an overall improvement of care for LEP patients. They appear to decrease communication errors, increase patient comprehension, equalize health care utilization, improve clinical outcomes, and increase satisfaction with communication and clinical services for limited English proficient patients.
We examined the studies in three different groups, those that compared the effect of professional and ad hoc interpreters, those that only examined the effect of professional interpreters (compared with either a noninterpreted LEP group, another type of professional interpreter, or most commonly, a language concordant group), and those that did not separate out the effect of professional and ad hoc interpreters. We found that professional interpreters improve clinical care more than ad hoc interpreters do, and that they can raise the quality of clinical care for LEP patients to match or approach that for patients without a language barrier. Even when the effect of professional interpreters is not separated out from that of ad hoc interpreters, there is evidence for a benefit. However, the results in this group of studies are not as strong or consistent.
Weaknesses in study design and analyses make it difficult to assess the full effects of medical interpretation on provision of health care. Only a third of studies used a standardized measure to identify participants' need for an interpreter. Even among the studies using a standardized measure, several asked about patients' primary language, but did not establish proficiency in the majority language, usually English. Thus, it is likely that the study populations included patients with varying language proficiency in the majority language, ranging from no proficiency to excellent proficiency. This variation in proficiency is likely to weaken the positive effect of interpreter use by including patients who may not have had a significant language barrier in both the interpreted and un-interpreted groups, thus decreasing any measurable difference between the groups. This is particularly true for small studies which have less statistical power to find differences in the first place. Therefore interpreters may be even more effective in improving communication and closing the gap in health disparities than the current literature suggests.
A quarter of the articles did not adequately separate the effects of different types of interpreters used, and half did not make it clear whether or not the professional interpreters in the study had undergone any training. Medical interpreting is a field in evolution, with the ongoing development of standards of practice and codes of ethics (NCIHC 2001
). Currently, training ranges from several hours to more than a year; this variation may result in a wide range of competency levels among professional medical interpreters. Of course, ad hoc interpreters—such as friends, family members, secretarial or custodial staff—have no training at all and their fluency in both English and their native language is not known. Not surprisingly then, the results of the studies in which the impact of ad hoc and professional interpreters is combined are often mixed. When only professional interpreters are used, the findings are more consistent; all studies which clearly identified the effect of professional interpreters show better results with use of interpreters.
Lastly, there are analytic limitations to the literature reviewed. All but one of the included publications presented observational data (Hornberger et al. 1996
), and many of the quantitative articles reviewed did not control for potential confounding in their analyses. It is possible that something other than interpreter use could have accounted for some of the differences between groups. Most of the utilization articles, however, had large numbers of patients, lending these studies enough statistical power to find differences between groups. In addition, they did control for potential confounding, and overall showed a beneficial effect of professional interpreters on LEP patients' utilization of clinical care. With the exception of preventive services, we were unable to evaluate whether each individual's use of services was medically appropriate. However, the studies did demonstrate that when interpreters were used, LEP patients' utilization rates generally approached or equaled those of English-speaking patients.
It is likely that the improved utilization and clinical outcomes are mediated by the ability of professional interpreters to overcome health communication barriers. Professional interpreters, through their experience, training, and knowledge of both medical and lay terminology are better able to communicate patients' symptoms and questions to clinicians, and clinicians' rationale for treatment and explanations of proper use of therapy to patients. Lower interpretation error rates and improved patient comprehension likely lead to greater patient acceptance of tests, adherence to follow-up and treatments, and thus improved health outcomes. However, there is a relative paucity of studies focused on either patient comprehension or clinical outcomes with adequate comparison groups, numbers, and analytic techniques.
Our review was limited by several factors. The majority of studies in our review were conducted in the United States in limited clinical contexts and our conclusions may not be easily generalized to other countries, cultures or clinical contexts. In addition, our search was conducted in English only, and ended in September 2005. While we conducted an extensive search, it is possible that we missed some articles. Of note, an update of the search strategies in January 2006 identified one additional article that met our inclusion criteria (Cohen et al. 2005
). This study viewed a request for an interpreter as a marker of a language barrier, and overall found no association between the risk for serious medical events and a family's request for interpreters. However, a subgroup of Spanish-speaking families requesting interpreters had a two-fold increased risk for serious medical events compared with patients not requesting interpreters. It is possible that we have missed other important studies on this topic published in non-English language peer-reviewed journals. We are reassured that our methodology did capture three studies in non-English speaking countries, and a quarter of the reviewed studies were conducted outside of the United States.
A lack of formal cost analyses of professional interpreters in the published literature precluded us from drawing any conclusions about the cost and cost-benefits of these services. The only such study that we are aware of did find a reasonable cost to benefit ratio of implementing trained, professional interpreter services in a large health maintenance organization (Jacobs et al. 2004
). There is also little research describing the costs to not providing these services. This leaves many small health care practices and organizations wondering if the benefits described in our review are worth the cost. Clearly there is a need for more research on the costs of language barriers and the cost-benefits of providing professional interpreter services.
Conclusion and Implications
Health care providers need to recognize that language barriers place LEP patients at a disadvantage that can be overcome by providing better linguistic access. Without access to professional interpreters, this large and growing population will continue to suffer differentials in both health and access to quality health care. Future research will contribute most to this area by focusing on how interpreters can decrease errors in comprehension and improve clinical outcomes, as well as studying the cost-effectiveness of these interventions.
We found that use of professional interpreters is associated with improved quality of health care for patients with limited English proficiency, and that professional interpreter use is likewise associated with a positive impact that is greater than that of ad hoc interpreters. Despite some important weaknesses in the literature, the findings suggest that provision of professional interpreter services can reduce disparities in care for LEP populations.