Composite Performance Measures Research Articles

Challenges of medical home transformation reported by 118 patient-centered medical home (PCMH) leaders.

Little is known about the most important organizational factors and strategies for transforming primary care clinics into patient-centered medical homes (PCMHs), so we studied this in newly certified medical homes in Minnesota. We collected the following information from the first 120 clinics serving adults to be certified: (1) a 105-item survey about the presence and function of practice systems now and 3 years ago; (2) standardized composite clinic performance measures for diabetes and cardiovascular disease; and (3) a 44-item survey about PCMH transformation derived from 31 qualitative interviews about barriers, facilitators, and change strategies with participants from 9 diverse clinics. The response rates for the systems survey was 92.5% and was 98.3% for the survey about transformation. Nearly all the items from the qualitative interviews identified as potentially important for transformation were strongly endorsed. Eighteen items in this survey also correlated significantly (P = <.01) with change in practice systems at the level of r ≥ 0.20. However, there was little relationship between these items and either absolute levels of systems or performance on composite measures of diabetes or vascular disease quality outcomes. Many items in the survey about transformation seem to have face validity for leaders of certified PCMHs and to be associated with the extent to which their clinics have made systems changes. While clinics may need to find their own unique path to transformation, the items identified here should be considered in those decisions.

The STS AVR + CABG Composite Score: A Report of the STS Quality Measurement Task Force

The Society of Thoracic Surgeons (STS) is developing a portfolio of composite performance measures for the most commonly performed adult cardiac procedures. This manuscript describes the third composite measure in this series, aortic valve replacement (AVR) combined with coronary artery bypass grafting surgery (CABG). We identified all patients in the STS Adult Cardiac Surgery Database who underwent AVR+CABG during recent 3-year (July 1, 2009, through June 30, 2012) and 5-year (July 1, 2007, through June 30, 2012) periods. Variables from the STS risk model for AVR+CABG were used to adjust morbidity and mortality outcomes. Evidence for internal mammary artery use in AVR+CABG was examined. We compared composite measures constructed using 3 or 5 years of outcomes with Bayesian credible intervals of 90%, 95%, or 98%. The final STS AVR+CABG composite performance measure is based on 3 years of data and 95% credible intervals. It includes risk-adjusted mortality and morbidity but not internal mammary artery use. Median composite score is 91.0% (interquartile range, 89.5% to 92.2%). There were 2.6% (24 of 915) one-star (lower performing) and 6.5% (59 of 915) three-star (higher performing) programs. Morbidity and mortality decrease monotonically as star ratings increase. The percentage of three-star programs increased substantially among programs that performed more than 150 procedures over 3 years compared with those performing 25 to 50 procedures (32.8% versus 1.6 %). Measure reliability was 0.51. The STS has developed a composite performance measure for AVR+CABG based on 3-year data samples and 95% credible intervals. This composite measure identified 9.1% of STS participants as having higher or lower than expected performance.

Can composite performance measures predict survival of patients with colorectal cancer?

To assess the relationship between long-term colorectal patient survival and methods of calculating composite performance scores. The Taiwan Cancer Database was used to identify patients who underwent bowel resection for colorectal adenocarcinoma between 2003 and 2004. Patients were assigned to one of three cohorts based on tumor staging: cohort 1, colon cancer stage < III; cohort 2, colon cancer stage III; cohort 3, rectal cancer. A composite performance score (CPS) was calculated for each patient using five different aggregating methods, including all-or-none, 70% standard, equal weight, analytic hierarchy process (AHP), and principal component analysis (PCA) algorithms. The relationships between CPS and five-year overall, disease-free, and disease-specific survivals were evaluated by a Cox proportional hazards model. A goodness-of-fit analysis for all five methods was performed using Akaike's information criterion. A total of 3272 colorectal cancer patients (cohort 1, 1164; cohort 2, 790; cohort 3, 1318 patients) with a mean age of 65 years were enrolled in the study. Bivariate correlation analysis showed that CPS values from the equal weight method were highly correlated with those from the AHP method in all cohorts (all P < 0.05). Multivariate Cox hazards analysis showed that CPS values derived from equal weight and AHP methods were significantly associated with five-year survivals of patients in cohorts 1 and 2 (all P < 0.05). In these cohorts, higher CPS values suggested a higher probability of five-year survival. However, CPS values derived from the all-or-none method did not show any significant process-outcome relationship in any cohort. Goodness-of-fit analyses showed that CPS values derived from the PCA method were the best fit to the Cox proportional hazards model, whereas the values from the all-or-none model showed the poorest fit. CPS values may highlight process-outcome relationships for patients with colorectal cancer in addition to evaluating quality of care performance.

The Market Orientation–Performance Relationship: The Empirical Link in Export Ventures

This study examines the empirical link between three dimensions of market orientation, namely, customer orientation, competitor orientation and interfunctional coordination, and overall export marketing performance in Indonesian export market ventures. The study was based on an empirical investigation of firms involved in exporting to foreign countries from Indonesia. The primary data for the study were collected from a self‐administered mail survey of 877 export market ventures from the manufacturing sector in Indonesia resulting in a sample of 109 usable responses being returned. From the application of the multiple regression analysis it was concluded that all three dimensions of market orientation had a significant impact on export marketing performance when measured via a composite measure of export marketing performance that included economic indicators, strategic indicators, and satisfaction with performance. © 2013 Wiley Periodicals, Inc.

Midlife Iron Status Is Inversely Associated with Subsequent Cognitive Performance, Particularly in Perimenopausal Women

The link between iron status and cognition has been established in infants and children, yet evidence in adults is scant and heterogeneous. We examined sex- and menopause-specific cross-time associations of iron status with cognition in the French Supplémentation en Vitamines et Minéraux Antioxydants Study cohort (1539 men, 1431 pre-/perimenopausal women, 962 postmenopausal women). Serum ferritin and hemoglobin data were obtained in 1995. Cognition was assessed after a mean of 13 y through 6 validated instruments, including the RI-48 cued recall test, phonemic and semantic fluency tasks, forward and backward digit span tasks, and a trail-making test. The standardized individual test scores were summed to form a composite cognitive performance measure. Associations between ferritin and hemoglobin and subsequent cognitive performance were examined through multivariable linear regression. Among men, no significant associations were observed. In postmenopausal women, an inverse association was found between ferritin and phonemic fluency (adjusted β: −0.11; 95% CI: −0.21, −0.01). Significant inverse associations between ferritin and both the composite cognitive measure (adjusted β: −0.09; 95% CI: −0.17, −0.00) and the forward digit span scores (adjusted β: −0.13; 95% CI: −0.22, −0.03) were observed only among premenopausal women aged ≥46 y at baseline. No significant findings with hemoglobin emerged. This study supports an inverse association between midlife iron status and subsequent cognitive performance that is sex- and menopause-dependent. Given the urgent need for prevention research on age-related disorders, future investigations of iron status and cognition are warranted. The study is registered at www.clinicaltrials.gov as NCT00272428.

Relationship between Stroop performance and resting state functional connectivity in cognitively normal older adults.

Early biomarkers of Alzheimer's disease (AD) are needed for developing therapeutic interventions. Measures of attentional control in Stroop-type tasks discriminate healthy aging from early stage AD and predict future development of AD in cognitively normal individuals. Disruption in resting state functional connectivity MRI (rs-fcMRI) has been reported in AD and in healthy controls at risk for AD. We explored the relationship among Stroop performance, rs-fcMRI, and CSF Aβ₄₂ levels in cognitively normal older adults. A computerized Stroop task (along with standard neuropsychological measures), rs-fcMRI, and CSF were obtained in 237 cognitively normal older adults. We compared the relationship between Stroop performance, including measures from reaction distributional analyses, and composite scores from four resting state networks (RSNs; default mode [DMN], salience [SAL], dorsal attention [DAN], and sensory-motor [SMN]), and the modulatory influence of CSF Aβ₄₂ levels. A larger Stroop effect in errors was associated with reduced rs-fcMRI within the DMN and SAL. Reaction time (RT) distributional analyses indicated the slow tail of the RT distribution was related to reduced rs-fcMRI functional connectivity within the SAL. Standard psychometric measures were not related to RSN composite scores. A relationship between Stroop performance and DMN (but not SAL) functional connectivity was stronger in CSF Aβ₄₂-positive individuals. A link exists between RSN composite scores and specific attentional performance measures. Both measures may be sensitive biomarkers for AD.

The Impact of Education and Acculturation on Nonverbal Neuropsychological Test Performance Among Latino/a Patients with Epilepsy

The present study examined the relationship between various sociocultural factors (e.g., acculturation, education), neurological variables (e.g., epilepsy duration and seizure frequency) and nonverbal neuropsychological (NP) test performance in a sample of 305 Latino/a and Non-Latino/a White adults with and without epilepsy. All participants completed nonverbal NP measures of visuospatial skills, memory, executive functioning, and psychomotor speed. An acculturation scale was administered to Spanish-speaking epilepsy patients and controls. Education was strongly correlated with performance on all but one of the nonverbal measures across the entire sample. Among Spanish-speaking Latino/a patients with epilepsy, level of acculturation to U.S. culture was associated with a measure of behavioral inflexibility (p < .05) and with a composite measure of nonverbal NP test performance (p < .05). Finally, the results of hierarchical regression models showed that sociocultural factors accounted for a greater proportion of variance in nonverbal NP test performance than did neurological factors. These results provide further evidence that sociocultural factors are strong predictors of NP test performance in clinical populations, even on nonverbal tests. Assessment of acculturation may be as critical as assessment of disease factors in interpreting cognitive performance in Latino/a individuals.

An assessment of composite measures of hospital performance and associated mortality for patients with acute myocardial infarction. Analysis of individual hospital performance and outcome for the National Institute for Cardiovascular Outcomes Research (NICOR)

To investigate whether a hospital-specific opportunity-based composite score (OBCS) was associated with mortality in 136,392 patients with acute myocardial infarction (AMI) using data from the Myocardial Ischaemia National Audit Project (MINAP) 2008-2009. For 199 hospitals a multidimensional hospital OBCS was calculated on the number of times that aspirin, thienopyridine, angiotensin-converting enzyme inhibitor (ACEi), statin, β-blocker, and referral for cardiac rehabilitation was given to individual patients, divided by the overall number of opportunities that hospitals had to give that care. OBCS and its six components were compared using funnel plots. Associations between OBCS performance and 30-day and 6-month all-cause mortality were quantified using mixed-effects regression analysis. Median hospital OBCS was 95.3% (range 75.8-100%). By OBCS, 24.1% of hospitals were below funnel plot 99.8% CI, compared to aspirin (11.1%), thienopyridine (15.1%), β-blockers (14.7%), ACEi (19.1%), statins (12.1%), and cardiac rehabilitation (17.6%) on discharge. Mortality (95% CI) decreased with increasing hospital OBCS quartile at 30 days [Q1, 2.25% (2.07-2.43%) vs. Q4, 1.40% (1.25-1.56%)] and 6 months [Q1, 7.93% (7.61-8.25%) vs. Q4, 5.53% (5.22-5.83%)]. Hospital OBCS quartile was inversely associated with adjusted 30-day and 6-month mortality [OR (95% CI), 0.87 (0.80-0.94) and 0.92 (0.88-0.96), respectively] and persisted after adjustment for coronary artery catheterization [0.89 (0.82-0.96) and 0.95 (0.91-0.98), respectively]. Multidimensional hospital OBCS in AMI survivors are high, discriminate hospital performance more readily than single performance indicators, and significantly inversely predict early and longer-term mortality.

A randomised controlled study to evaluate the effectiveness of targeted occupational health and safety consultation or inspection in Ontario manufacturing workplaces

ObjectiveFrom 2004 to 2008, the prevention system in Ontario, Canada ran the High Risk Firm Initiative, an injury-experience based targeted consultation or inspection programme. Our objective was to establish whether...

Does Systematic Adherence to Joint Commission and AHA Heart Failure Performance Measures Improve Patient Outcomes?

Author(s): Bender, M; Jaski, BE; Glaser, D; Thomas, V; Cary, DS; Smith, SC | Abstract: Introduction It is unclear whether inpatient heart failure (HF) performance measures reduce post-discharge adverse events. This exploratory study examined the association between systematic adherence to a set of performance measures and outcomes. Measures included all four Joint Commission (JC) HF core measures and AHA recommended beta blockade prescription on discharge. Methods A retrospective review of a 3-hospital system was performed for all patients discharged with a primary diagnosis of HF in 2008-2009. Patients were included if they met eligibility criteria for one or more measures (n=1270). ‘Perfect care’ was defined as compliance with all eligible measures. Subsequent all-cause 30-day readmission and 1-year mortality was determined via electronic records and social security national database. Results ‘Perfect care’ significantly reduced 30-day readmissions (19.2% vs. 24.9%, p=.045; OR=.72, 95% CI 0.52-0.99). ‘Perfect care’ did not influence 1-year mortality. Conclusions Adherence to this set of composite performance measures positively influenced short-term patient outcomes. Benefit of adherence was found despite the longer LOS and higher severity of illness on index admission for patients receiving ‘perfect care’. The data support the clinical value of a systematic approach towards HF care on patient care quality. ‘Perfect care’ did not influence long term outcomes, which may be because inpatient processes do not extend to long term outpatient medical management.

Age and Gender Differences in Quality of Care and Outcomes for Patients with ST-segment Elevation Myocardial Infarction

BackgroundYoung patients (aged≤45 years) presenting with ST-segment elevation myocardial infarction present unique challenges. The quality of care and in-hospital outcomes may differ from their older counterparts. MethodsA total of 31,544 patients presenting with ST-segment elevation myocardial infarction and enrolled in the American Heart Association's Get With the Guidelines Coronary Artery Disease registry were analyzed. The cohort was divided into those aged 45 years or less and those aged more than 45 years. ResultsYoung patients accounted for 10.3% of all ST-segment elevation myocardial infarction cases. Compared with older patients, younger patients were less likely to have traditional cardiovascular risk factors and had similar or better quality/performance measures with lower in-hospital mortality (unadjusted rate 1.6 vs 6.5%, P<.0001; adjusted odds ratio [OR], 0.37; 95% confidence interval [CI], 0.29-0.46). Time trend analysis (2002-2008) suggested an increase over time in the “all or none” composite performance measure in both the younger and older patients (68%-97% and 69%-96%, respectively). However, there was significantly lower quality of care and worse outcomes in women (vs men) and in the very young (≤35 vs 36-45 years). Significant interaction was seen between age and gender for in-hospital death, such that the gender difference was greater in the younger cohort. Similar interaction was seen for door-to-thrombolytic time such that the gender delay was greater in the younger cohort (women:men ratio of means=1.73, 95% CI, 1.21-2.45 [younger] vs 1.08, 95% CI, 1.00-1.18 [older]; Pinteraction=.0031). ConclusionYoung patients aged 45 years or less presenting with ST-segment elevation myocardial infarction overall had similar quality of care and in-hospital outcomes as older counterparts. However, quality of care was significantly lower and mortality was higher in young women (vs young men) and the very young (≤35 vs 36-45 years).

Sustainability as Adaptability

Most corporations now view sustainability as a key requirement for competitive advantage, but few claim to have achieved it. One of the key obstacles separating intention from execution is that the sustainability frameworks employed by companies tend to be insufficiently clear, precise, or comprehensive to guide decision making. One of the most pressing challenges for corporate leaders today is, of course, to sustain the economic viability of the core businesses. But given the implicit “beyond business” focus of most sustainability efforts, corporate executives would be better served by a more integrated, holistic framework—one that enables them to make tradeoffs among the economic, social, and ecological aspects of business.This article introduces such a framework—one that redefines sustainability as the ability of companies to adapt to change in three different spheres of operation—ecological, social, and economic—with a near‐term as well as a longer‐term planning horizon. Without such adaptation, business models become obsolete for reasons that can range from economic failure, to competitive inferiority, to social or ecological limits.This ability to adapt can be measured and valued by using the BCG Adaptive Advantage Index, a composite measure of corporate performance during market downturns. The BCG analysis also shows that although the most adaptive companies tend to report lower profits and have lower values during periods of relative stability, such companies perform consistently better over full cycles.Creating social and ecological value alone doesn't automatically confer economic rewards, but—with the right business model and capabilities—it can. The authors explore some of the business model archetypes that successfully achieve this “co‐optimization.”

Comparison of the Frontal Systems Behavior Scale and Neuropsychological Tests of Executive Functioning in Predicting Instrumental Activities of Daily Living

Both neuropsychological tests of executive functioning and the Frontal Systems Behavior Scale (FrSBe) consistently predict instrumental activity-of-daily-living capacity. However, the nature of the predictive relationship between the FrSBe and neuropsychological tests of executive functioning has received limited attention. The current study was designed to assess the incremental validity of the FrSBe in predicting instrumental activity-of-daily-living functioning when added to comprehensive testing of executive functioning in a sample of 100 adult general neuropsychological referrals. A composite measure of executive test performance was calculated, and a family member completed the FrSBe and an instrumental activity-of-daily-living measure. Stepwise multiple regression analysis using the executive composite measure and the FrSBe accounted for 44% of the variance in instrumental activity capacity, and the addition of the FrSBe increased predictive ability by approximately 50%. The current results also indicate that FrSBe Scale E is more important as a predictor of instrumental activity capacity than the two self-regulation measures, Scale A and Scale D.

Are performance measures equally stable?

Managed portfolio performance evaluation is an important issue from both academics’ and investors’ points of view. One important aspect concerns the choice of the measure used to assess performance, because each index offers a different perspective about the trade-off between return level and risk exposure. A related crucial issue is the stability of measures over time and, hence, their predictive power about future results. In this work, we address the problem of evaluating of the stability of a performance measure. First, we discuss the use of alternative criteria to measure stability and propose a stability index based on changes of ranks over several periods of time. We also propose a statistical test to evaluate the homogeneity of the stability of alternative performance measures. Second, we suggest a composite performance measure, built as a linear combination of various indexes, specifically conceived to be maximally stable over time while preserving information about risk-adjusted return behavior. An application to a set of US mutual funds belonging to the Large Blend category shows how these methods work.

Older adults have greater difficulty imagining future rather than atemporal experiences.

Episodic future thinking refers to mentally traveling forward in time to preexperience an event, and emerging research suggests that this is more difficult for older adults. The current study was designed to better understand the effect of aging on separate component processes of age differences in episodic future thinking. Young (n = 24) and older (n = 25) adults were asked to construct a) atemporal scenarios, b) future scenarios, and c) a narrative that involved navigation. Each of these conditions assesses the capacity to construct and describe a scene, but only the future scenario requires a subjective sense of self in time (autonoetic consciousness). The composite measure of performance showed that relative to young adults, older adults have substantially reduced capacity for all three types of construction, suggesting that age-related difficulty imagining future episodic events may reflect a more general cognitive decline with age. In addition, older adults were worse at imagining future experiences than atemporal experiences, indicating limited capacity for autonoetic consciousness. Further, this difference between imagining atemporal and future experiences was not as evident among younger adults. These deficits in episodic future thinking have implications for the daily lives of older adults in terms of anticipating and planning for the future.

Comparison of Composite Measure Methodologies for Rewarding Quality of Care

Composite indices of health care performance are an aggregation of underlying individual performance measures and are increasingly being used to rank hospitals. We sought to conduct an observational analysis to determine the influence of the opportunity-based and all-or-none composite performance measures on hospital rankings. We examined 194 245 patients hospitalized with acute myocardial infarction between July 2006 and June 2009 from 334 hospitals participating in the Get With The Guidelines--Coronary Artery Disease (GWTG-CAD) quality improvement program. We analyzed hospital opportunity-based and all-or-none composite scores and 30-day risk-standardized all-cause mortality and readmission rates. We found that the median calculated opportunity-based score for these hospitals was 95.5 (interquartile range, 90.4, 98.0). The median all-or-none score was 88.9 (interquartile range, 79.7, 94.4). The 2 scoring methods were significantly correlated with one another (r=0.98, P<0.001). Rankings generated by the two methods were significantly correlated (r=0.93, P<0.001). The two methods had a modest correlation with the 30-day risk-standardized mortality rate (opportunity-based score: r=-0.25, P<0.001; all-or-none score: r=-0.24, P<0.001). Neither composite measure correlated with the 30-day risk-standardized readmission rate. Over time, the number of hospitals new to the top and bottom quintiles of hospital rankings diminished similarly for both composite measures. When including additional performance measures into the composite score, the two methods produced similar changes in hospital rankings. The opportunity-based and all-or-none coronary artery disease composite indices are highly correlated and yield similar ranking of the top and bottom quintiles of hospitals. The two methods provide similarly modest correlations with 30-day mortality, but not readmission.

Pilot Candidate Selection Method

In 1993, the US Air Force implemented the Pilot Candidate Selection Method (PCSM) as an additional indicator of pilot training aptitude. PCSM scores have been shown to be related to several pilot training criteria including graduation/elimination, flying grades, class rank, and number of flight hours needed to complete training ( Carretta &amp; Ree, 2003 ). The PCSM composite is still in use today, but the scores that contribute to it have changed. The study reported here examined the predictive validity of the current composite versus several training performance measures for 883 students attending Specialized Undergraduate Pilot Training (SUPT). Results indicated that the PCSM composite remained predictive of flying training performance despite changes in test content and flying training. After correction for multivariate range restriction and dichotomization of the graduation/elimination criterion, the correlation between the PCSM composite and T-6 completion was .53. This is consistent with the value of .46 reported by Carretta and Ree (2003) for an earlier version of the PCSM composite. Its predictiveness can be attributed to the measurement of factors that have consistently shown a relation to flying performance: cognitive ability, aviation job knowledge/experience, and psychomotor ability.

Patient and Practice Factors Associated With Improvement in Use of Guideline-Recommended Therapies for Outpatients With Heart Failure (from the IMPROVE HF Trial)

Diverse factors are associated with variations in evidence-based treatment of outpatients with heart failure (HF). However, patient and practice characteristics associated with improved use of guideline-recommended therapies over time have not been well studied. The Registry to Improve the Use of Evidence-Based Heart Failure Therapies in the Outpatient Setting (IMPROVE HF) is a prospective evaluation of a performance improvement initiative conducted at 167 practices treating outpatients with diagnosed HF or previous myocardial infarction and left ventricular ejection fraction ≤35%. Patient characteristics and care practice data were collected by chart abstraction at baseline and 24 months for 14,236 patients. Seven individual care measures and a composite measure were assessed. Practices were stratified by tertiles of composite measure improvement, and significant, independent patient and practice factors associated with improvement in the composite measure at 24 months were examined. The baseline composite performance measure was 68.4%, which increased to 80.1% at 24 months (+11.6%, p <0.001). The composite measure improvement tertiles were ≤8%, >8% to 15%, and >15%. Multivariate analyses revealed greater improvements associated only with lower practice baseline composite measure rates (p <0.001). Logistic regression showed that 2 additional variables were inversely associated with practices in the highest tertile in composite measure improvement (>15%): southern practice location (p = 0.0239) and edema (p = 0.0047). In conclusion, few patient and practice factors were associated with greater or lesser overall improvements over time in the use of guideline-recommended HF therapies. Other factors may be more important determinates of the magnitude of care improvements over time among cardiology practices participating in a performance improvement initiative.

Measuring Physicians’ Performance in Clinical Practice: Reliability, Classification Accuracy, and Validity

Much research has been devoted to addressing challenges in achieving reliable assessments of physicians' clinical performance but less work has focused on whether valid and accurate classification decisions are feasible. This study used 957 physicians certified in internal medicine (IM) or a subspecialty, who completed the American Board of Internal Medicine (ABIM) Diabetes Practice Improvement Module (PIM). Ten clinical and two patient-experience measures were aggregated into a composite measure. The composite measure score was highly reliable (r = .91) and classification accuracy was high across the entire score scale (>0.90), which indicated that it is possible to differentiate high-performing and low-performing physicians. Physicians certified in endocrinology and those who scored higher on their IM certification examination had higher composite scores, providing some validity evidence. In summary, it is feasible to create a psychometrically robust composite measure of physicians' clinical performance, specifically for the quality of care they provide to patients with diabetes.

The effects of visibility conditions, traffic density, and navigational challenge on speed compensation and driving performance in older adults

Research on how older drivers react to natural challenges in the driving environment is relevant for both the research on mental workload and that on age-related compensation. Older adults ( M age = 70.8 years) were tested in a driving simulator to assess the impact of three driving challenges: a visibility challenge (clear day, fog), a traffic density challenge (low density, high density) and a navigational challenge (participants followed the road to arrive at their destination, participants had to use signs and landmarks). The three challenge manipulations induced different compensatory speed adjustments. This complicated interpretation of the other measures of driving performance. As a result, speed adjustment indices were calculated for each condition and participant and composite measures of performance were created to correct for speed compensation. (These speed adjustment indices correlated with vision test scores and subscales of the Useful Field of View ®.) When the composite measures of driving performance were analyzed, visibility × density × navigational challenge interactions emerged for hazard RT and SD of lane position. Effects were synergistic: the impact of the interaction of challenge variables was greater than the sum of independent effects. The directions of the effects varied depending on the performance measure in question though. For hazard RT, the combined effects of high-density traffic and navigational challenge were more deleterious in good visibility conditions than in fog. For or SD of lane position, the opposite pattern emerged: combined effects of high-density traffic and navigational challenge were more deleterious in fog than in clear weather. This suggests different aspects of driving performance tap different resources.