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This article is part of a For-Discussion-Section of Methods of Information in Medicine about the paper "Combining Health Data Uses to Ignite Health System Learning" written by John D. Ainsworth and Iain E. Buchan [1]. It is introduced by an editorial. This article contains the combined commentaries invited to independently comment on the paper of Ainsworth and Buchan. In subsequent issues the discussion can continue through letters to the editor. With these comments on the paper "Combining Health Data Uses to Ignite Health System Learning", written by John D. Ainsworth and Iain E. Buchan [1], the journal seeks to stimulate a broad discussion on new ways for combining data sources for the reuse of health data in order to identify new opportunities for health system learning. An international group of experts has been invited by the editor of Methods to comment on this paper. Each of the invited commentaries forms one section of this paper. [ABSTRACT FROM AUTHOR]

Objectives: To study the association between organisational downsizing and subsequent musculoskeletal problems in employees and to determine the association with changes in psychosocial and behavioural risk factors.Methods: Participants were 764 municipal employees working in Raisio, Finland before and after an organisational downsizing carried out between 1991 and 1993. The outcome measures were self reports of severity and sites of musculoskeletal pain at the end of 1993 and medically certified musculoskeletal sickness absence for 1993-5. The contribution of changes in psychosocial work characteristics and health related behaviour between the 1990 and 1993 surveys was assessed by adjustment.Results: After adjustment for age, sex, and income, the odds ratio (OR) for severe musculoskeletal pain between major and minor downsizing and the corresponding rate ratios for musculoskeletal sickness absence were 2.59 (95% confidence interval (95% CI) 1.5 to 4.5) and 5.50 (3.6 to 7.6), respectively. Differences between the mean number of sites of pain after major and minor downsizing was 0.99 (0.4 to 1.6). The largest contribution from changes in work characteristics and health related behaviour to the association between downsizing and musculoskeletal problems was from increases in physical demands, particularly in women and low income employees. Additional contributory factors were reduction of skill discretion (relative to musculoskeletal pain) and job insecurity. The results were little different when analyses were confined to initially healthy participants.Conclusions: Downsizing is a risk factor for musculoskeletal problems among those who remain in employment. Much of this risk is attributable to increased physical demands, but adverse changes in other psychosocial factors may also play a part. [ABSTRACT FROM AUTHOR]

Background Whether the higher coronary mortality in South Asians compared with White populations is due to a higher incidence of disease is not known. This study assessed cumulative incidence of chest pain in South Asians and Whites, and prognosis of chest pain. Methods Over seven phases of 18-year follow-up of the Whitehall-II study (9775 civil servants: 9195 White, 580 South Asian), chest pain was assessed using the Rose questionnaire. Coronary death/non-fatal myocardial infarction was examined comparing those with chest pain to those with no chest pain at baseline. Results South Asians had higher cumulative frequencies of typical angina by Phase 7 (17.0 versus 11.3%, P < 0.001) and exertional chest pain (15.4 versus 8.5%, P < 0.001) compared with Whites. Typical angina and exertional chest pain at baseline were associated with a worse prognosis compared with those with no chest pain in both groups (typical angina, South Asians: HR, 4.67 and 95% CI, 2.12–0.30; Whites: HR, 3.56 95% CI, 2.59–4.88). Baseline non-exertional chest pain did not confer a worse prognosis. Across all types of pain, prognosis was worse in South Asians. Conclusion South Asians had higher cumulative incidence of angina than Whites. In both, typical angina and exertional chest pain were associated with worse prognosis compared with those with no chest pain. [ABSTRACT FROM PUBLISHER]

We determined the degree to which metabolic syndrome components, inflammation and health behaviours account for the social gradient in CHD. A total of 5312 men, initially aged 39 to 63 years, were followed for 13.1 years for incident coronary death or non-fatal myocardial infarction according to socioeconomic position (employment grade). The contribution of explanatory factors to socioeconomic differences in CHD was assessed by the reduction in hazard ratios computed using Cox models. The effects of measurement error were taken into account. Coronary events were more common in lower employment grades than in higher, with a hazard ratio (relative index of inequality) of 2.2 (95% CI 1.3–3.7), after adjustment for age and ethnic group. Behavioural risk factors (mainly smoking and diet) explained a third of the socioeconomic gradient in CHD incidence. Components of the metabolic syndrome and inflammatory markers predicted CHD incidence and also explained a third of the gradient. Combined, these two groups of predictors, i.e. behavioural and biological, accounted for over half of the socioeconomic gradient in incident CHD. Adding body height as a marker of the effects of early life increased this figure to about 60%. A major question has been how someone’s socioeconomic position can lead to increased risk of CHD. Socioeconomic differences in components of the metabolic syndrome (and inflammatory markers) provide part of the answer. This was, to an important degree, independent of the contribution of health behaviours to the socioeconomic differentials in CHD. [ABSTRACT FROM AUTHOR]

Aims Diabetes is thought to be associated with increased risk of sickness absence in working populations. We examined the contribution of co-morbidity to this association. Methods Records of physician-certified sickness absence episodes (> 3 days) over a 1-year period were obtained from employers’ records after a survey of chronic diseases and risk factors in 638 diabetic and 32 510 non-diabetic public sector employees in Finland (the Public Sector Study). Results Diabetic employees had a 2.15-fold (95% confidence interval 1.92–2.40) age- and sex-adjusted excess risk of sickness absence compared with their colleagues with no chronic disease. In absolute terms, diabetes was related to 59 extra absence episodes per 100 person years. Of this excess risk, 55% was attributable to co-occurring non-cardiovascular diseases, such as depression, prolapsed intervertebral disc and bronchitis. The contribution of cardiovascular complications to the excess sickness absence was small (7%). Conclusions In this occupational cohort, the excess risk of sickness absence in diabetic employees was largely accounted for by non-cardiovascular co-morbidity. Intervening multiple chronic conditions may be important in programmes to reduce sickness absence in diabetic employees. [ABSTRACT FROM AUTHOR]

Objective: To determine whether cardiothoracic ratio (CTR), within the range conventionally considered normal, predicted prognosis in patients undergoing coronary angiography. Design: Cohort study with a median of 7-years follow-up. Setting: Consecutive patients undergoing coronary angiography at Barts and The London National Health Service (NHS) Trust. Subjects: 1005 patients with CTRs measured by chest radiography, and who subsequently underwent coronary angiography. Of these patients, 7.3% had a CTR > or =0.5 and were excluded from the analyses. Outcomes: All-cause mortality and coronary event (non-fatal myocardial infarction or coronary death). Adjustments were made for age, left ventricular dysfunction, ACE inhibitor treatment, body mass index, number of diseased coronary vessels and past coronary artery bypass graft. Results: The risk of death was increased among patients with a CTR in the upper part of the normal range. In total, 94 (18.9%) of those with a CTR below the median of 0.42 died compared with 120 (27.8%) of those with a CTR between 0.42 and 0.49 (log rank test p<0.001). After adjusting for potential confounders, this increased risk remained (adjusted HR 1.45, 95% CI 1.03 to 2.05). CTR, at values below 0.5, was linearly related to the risk of coronary event (test for trend p = 0.024). Conclusion: In patients undergoing coronary angiography, CTR between 0.42 and 0.49 was associated with higher mortality than in patients with smaller hearts. There was evidence of a continuous increase in risk with higher CTR. These findings, along with those in healthy populations, question the conventional textbook cut-off point of > or =0.5 being an abnormal CTR. [ABSTRACT FROM AUTHOR]

Objective: To determine whether rapid access chest pain clinics are clinically effective by comparison of coronary event rates in patients diagnosed with angina with rates in patients diagnosed with non-cardiac chest pain and the general population. Design: Multicentre cohort study of consecutive patients with chest pain attending the rapid access chest pain clinics (RACPCs) of six hospitals in England. Participants: 8762 patients diagnosed with either non-cardiac chest pain (n = 6396) or incident angina without prior myocardial infarction (n = 2366) at first cardiological assessment, followed up for a median of 2.57 (interquartile range 1.96-4.15) years. Main outcome measures: Primary end point-death due to coronary heart disease (international Classification of Diseases (ICD)10 120-125) or acute coronary syndrome (non-fatal myocardial infarction (ICD10 121-123), hospital admission with unstable angina (124.0, 124.8, 124.9)). Secondary end points-all-cause mortality (lCD 120), cardiovascular death (ICD10 100-199), or non-fatal myocardial infarction or non- fatal stroke (160-169). Results: The cumulative probability of the primary end point in patients diagnosed with angina was 16.52% (95% confidence interval (CI) 14.88% to 18.32%) after 3 years compared with 2.73% (95% CI 2.29% to 3.25%) in patients with non-cardiac chest pain. Coronary standardised mortality ratios for men and women with angina aged <65 years were 3.52 (95% CI 1.98 to 5.07) and 4.39 (95% CI 1.14 to 7.64). Of the 599 patients who had the primary end point, 194 (32.4%) had been diagnosed with non-cardiac chest pain. These patients were younger, less likely to have typical symptoms, more likely to be south Asian and more likely to have a normal resting electrocardiogram than patients with angina who had the primary end point. Conclusion: RACPCs are successful in identifying patients with incident angina who are at high coronary risk, but there is a need to reduce misdiagnosis and improve outcomes in patients diagnosed with non-cardiac chest pain who accounted for nearly one third of cardiac events during follow-up. [ABSTRACT FROM AUTHOR]

ABSTRACT Objective To assess whether revascularisation that is considered to be clinically appropriate is also cost effective. Design Prospective observational study comparing cost effectiveness of coronary artery bypass grafting, percutaneous coronary intervention, or medical management within groups of patients rated as appropriate for revascularisation. Setting Three tertiary care centres in London. Participants Consecutive, unselected patients rated as clinically appropriate (using a nine member Delphi panel) to receive coronary artery bypass grafting only (n=815); percutaneous coronary intervention only (n=385); or both revascularisation procedures (n=520). Main outcome measure Cost per quality adjusted life year gained over six year follow-up, calculated with a National Health Service cost perspective and discounted at 3.5%/year. Results Coronary artery bypass grafting cost £22 000 (¿33 000; $43 000) per quality adjusted life year gained compared with percutaneous coronary intervention among patients appropriate for coronary artery bypass grafting only (59% probability of being cost effective at a cost effectiveness threshold of £30 000 per quality adjusted life year) and £19 000 per quality adjusted life year gained compared with medical management among those appropriate for both types of revascularisation (probability of being cost effective 63%). In none of the three appropriateness groups was percutaneous coronary intervention cost effective at a Threshold of £30 000 per quality adjusted life year. Among patients rated appropriate for percutaneous coronary intervention only, the cost per quality adjusted life year gained for percutaneous coronary intervention compared with medical management was £47 000, exceeding usual cost effectiveness thresholds; in these patients, medical management was most likely to be cost effective (probability 54%). Conclusions Among patients judged clinically appropriate for coronary revascularisation, coronary artery bypass gr [ABSTRACT FROM AUTHOR]

Objective: To estimate the need for coronary revascularisation, by using an incidence of indications approach, among 45-84 year olds with stable angina, unstable angina, and acute myocardial infarction. Design: Modelling exercise. Six key steps along the pathway of care from initial diagnosis in primary or secondary care to revascularisation were defined and the frequency of indications estimated using routine data from hospital admissions and data from studies in the general population, and primary and secondary care. Setting and patients: Mid-1998 population of England. Intervention: Coronary revascularisation. Main outcome measure: Ability to benefit (need), defined by randomised trials, expert panel ratings from the ACRE (appropriateness of coronary revascularisation) study, or by informal consensus. Results: The need for coronary revascularisation was estimated to be 92 000 procedures, equivalent to a rate of 1861 per million population. Overall, the model of need exceeded current provision by 3.3:1, although among people aged 75 years and over the ratio was 7.7:1. A plausible upper estimate of need-obtained by assuming that 90% of patients with stable angina were referred from primary care and that angiography would be performed in 65% of patients with acute myocardial infarction and 75% of patients with unstable angina—was 2626 per million population. Conclusions: The national target of 1500 revascularisation procedures per million population is credibly related to population need, although upper estimates of need are considerably higher. Better understanding is required of the benefits of referring patients with specific indications from primary care. The greatest relative increase in provision is required for those aged 75 and older, among whom trial evidence of benefit is scant. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the association between organizational downsizing and subsequent musculoskeletal problems in employees and determined association with changes in psychosocial and behavioral risk factors. Occurrence of musculoskeletal problems in workers across occupational groups; Mean percentages of work characteristics and percentages of health related behavior after downsizing; Implications for managerial strategies concerning health of employees.

STUDY OBJECTIVE: To determine the relative contribution of adult compared with early life socioeconomic status as predictors of morbidity attributable to coronary heart disease (CHD), chronic bronchitis and depression in the Whitehall II study of British civil servants. DESIGN: Prospective observational study with mean 5.3 years (range 3.7-7.6) follow up. SETTING: 20 civil service departments originally located in London. PARTICIPANTS: 6895 male and 3413 female office-based civil servants aged 35-55 years at baseline. OUTCOME MEASURES: New cases at follow up of CHD, chronic bronchitis and depression defined using validated questionnaires. MAIN RESULTS: Employment grade was inversely associated with CHD, chronic bronchitis and depression in men (odds ratio per unit decrease in grade 1.30, 1.44 and 1.20 respectively). Employment grade was strongly related to father's social class. Chronic bronchitis, in women, and depression, in men, were more common among those with fathers of higher social class. When mutual adjustment was made for father's social class, grade at entry to the civil service and current grade, the strongest effects on adult morbidity were found for current grade. Among participants in whom neither parent had died < or =70 years of age the inverse association with adult SES was maintained. CONCLUSIONS: Adult socioeconomic status was a more important predictor of morbidity attributable to coronary disease, chronic bronchitis and depression than measures of social status earlier in life. In this population, the importance of social circumstances early in life may be in the way they influence employment and social position and thus exposures in adult life. [ABSTRACT FROM AUTHOR]

To determine the impact of socioeconomic status (SES) on coronary heart disease (CHD) mortality in people with and without prevalent CHD at baseline. Cohort study with 25 year follow up; prevalent CHD was defined by Q, ST or T wave electrocardiographic (ECG) abnormalities or symptoms (defined by the Rose chest pain questionnaire and self reported doctor diagnosis) or both. SES was defined by four civil service employment grades. London. 17 907 male civil servants aged 40-69 years. CHD mortality (n=2695 deaths). The lowest versus highest employment grade was associated with increased CHD mortality (age adjusted hazard ratio 1.56 (95% CI 1.2, 2.1)), prevalence of symptoms and, among symptomatic participants only, the prevalence of Q, ST or T abnormalities. Thirty one per cent of CHD deaths occurred in participants with prevalent CHD at baseline. Among participants without Q, ST or T abnormality employment grade was associated with CHD mortality; the hazard ratios (lowest v highest grade) adjusted for age, systolic and diastolic blood pressure were 1.72 (95% CI 1.4, 2.1) for asymptomatic and 1.52 (95% CI 1.1, 2.1) for symptomatic participants; among participants with Q, ST or T abnormality the corresponding hazard ratios were 1.46 (95% CI 0.7, 2.9) and 1.14 (95% CI 0.6, 2.0) respectively. SES was inversely associated with CHD mortality in civil servants with and without prevalent CHD at baseline. Further distinguishing the relative contribution of SES to the initiation and progression of CHD requires repeated measures studies of pre-clinical and clinical measures of CHD. [ABSTRACT FROM AUTHOR]

Aim To examine the association of radiographic measures of heart size with mortality from coronary heart disease.Methods and Results One thousand, one hundred and ninety-one male civil servants aged 40-69 years were followed-up for mortality over 25 years in relation to cardiothoracic ratio and relative heart volume. A high cardiothoracic ratio and relative heart volume predicted coronary (n= 196 deaths) and all-cause mortality, but not respiratory or malignant mortality. After adjustment for age, systolic and diastolic blood pressure, the highest (≥0·47) compared to the lowest quintile of the cardiothoracic ratio (<0·40) was associated with a rate ratio of 1·84 (95% CI 1·14–2·97) for the effect on coronary heart disease mortality. Further adjustment for heart rate, smoking, cholesterol, angina and ECG ischaemia had little effect, reducing the rate ratio to 1·65 (95% CI 1·01–2·70). Similar rate ratios were observed for relative heart volume.Conclusions Cardiothoracic ratio within the range considered ‘normal’ in clinical practice predicted coronary heart disease mortality independent of established coronary heart disease risk factors. The relative heart volume, which uses measurements from the lateral as well as the posteroanterior chest X-ray, did not predict coronary heart disease any better than the cardiothoracic ratio. The extent to which left ventricular mass and systolic dysfunctionpathophysiological correlates of the cardiothoracic ratio and relative heart volume - are independent risk factors for coronary heart disease should be further investigated. [ABSTRACT FROM PUBLISHER]

OBJECTIVES: (i) To investigate the effects of current obesity, steady weight change and weight fluctuation on physical functioning and (ii) to determine whether associations are independent of coronary heart disease. DESIGN: Prospective cohort study with body mass index (BMI) measurements at four time points between the ages of 25 and 63 y. SETTING: British civil servants based in London offices at baseline. PARTICIPANTS: 6895 men and 3413 women aged 35–55 y at baseline. MAIN OUTCOME MEASURE: Physical functioning was assessed using the 10-item scale from the Short Form 36 Health Survey, with a score in the lowest quartile indicating poor physical functioning. RESULTS: After adjustment for age and confounders (employment grade, smoking, alcohol, exercise and menopausal status), current BMI was monotonically associated with poor physical functioning in women whereas a threshold effect at a BMI of 27 kg/m2 was seen in men. The odds ratio of poor physical functioning was 1.55 (95% confidence interval (CI) 1.02–2.35) amongst women and 1.04 (95% CI 0.77–1.41) amongst men with BMI 23–24.9 kg/m2 compared to those with BMI <21 kg/m2. Women in the upper, compared to the lower, tertile of steady weight change, had an odds ratio of poor physical functioning of 1.79 (1.24–2.60) after adjustment for age, confounders, current BMI and weight fluctuation. Women in the upper, compared to the lower, tertile of weight fluctuation had an odds ratio of poor physical functioning of 1.70 (1.23–2.34) adjusting for age, confounders, current BMI and steady weight change. Adjustment for the presence of coronary heart disease did not substantially alter any of these associations. Steady weight change and weight fluctuation had no independent effects in men. CONCLUSION: Among women, current obesity, steady weight change and weight fluctuation are independently and monotonically associated with poor physical... [ABSTRACT FROM AUTHOR]

(1) To identify behavioural and biological correlates of poor physical functioning and (2) to determine whether such associations are independent of disease. Potential correlates were obtained from questionnaires and screening visits at baseline and five year follow up. Physical functioning was measured at follow up using the 10 item scale from the short-form 36 health survey. London offices at baseline. 10,308 civil servants (6895 men and 3413 women), with a median age (range) of 49 years (39-63) at follow up. Multiple logistic regression showed that cigarette smoking, physical activity, body mass index (BMI), triglycerides, fibrinogen, and insulin were independently associated with poor physical functioning for men. For women, physical activity, eating habits, body mass index, fibrinogen, and insulin were independently associated with poor physical functioning. For example, among men, current smokers who had smoked more than 20 pack years were 1.89 (95% CI 1.35 to 2.67) times as likely to have poor physical functioning as never smokers. Men with BMI of 30 kg/m2 or more were 1.71 (95% CI 1.13 to 2.59) times as likely to have poor physical functioning as those with BMI < 20 kg/m2. The corresponding odds ratio for women was 2.66 (95% CI 1.80 to 3.93). With the exceptions of fibrinogen and insulin, associations remained on exclusion of subjects with physical disease. Risk factors established for physical diseases are associated with poor physical functioning in a population of working age. These associations may be independent of current disease. [ABSTRACT FROM AUTHOR]

Background: Mortality rates from hypertension related diseases such as coronary heart disease, hypertensive heart disease, stroke and end stage renal disease show an inverse association with socio-economic status (SES). Objectives: To review the published literature in order to assess whether (i) there is an association between SES and blood pressure (BP), and if so whether this is explained by (ii) SES differences in treatment rates, or (iii) SES differences in established risk factors for hypertension, or (iv) psycho-social factors associated with SES. Method: A narrative systematic review of published articles identified from a MEDLINE search from 1966-1996 and manual searching of the retrieved articles' bibliographies. Results: Lower SES was associated with higher mean BPs in almost all studies in developed countries. This inverse gradient was both stronger and more consistently found in women than in men. The magnitude of the association varied but generally was quite small, with age adjusted mean systolic BP differences of about 2-3 mm Hg between the highest and lowest SES groups. The finding of an SES gradient in BP, despite adjusting for treatment in some studies and the lack of consistent SES differences in hypertension treatment rates, makes differential treatment an unlikely explanation for the SES gradient in BP. A substantial part of the SES gradient was accounted for by the SES gradient in body mass index. Alcohol consumption across SES groups accounted for part of the association in men though few studies examined this issue specifically. In contrast, in undeveloped or developing countries a direct association between SES and BP has often been found which may reflect a higher prevalence of obesity, and higher salt and alcohol intakes among those of higher SES. The SES differences in BP were not detectable in most studies in children. There is little evidence that adverse psycho-social factors associated with low SES cause chronic elevations in BP... [ABSTRACT FROM AUTHOR]

Background Patients with COPD are at increased risk of myocardial infarction (MI) compared to the general population and have shorter survival after any MI. We investigated whether this held true in patients with an "unanticipated" MI, defined as an MI occurring as the first manifestation of atherosclerotic disease and without any traditional cardiovascular risk factors and without any prior chest pain. Methods All patients experiencing their first MI between 1st January 2003 and 31st December 2008 as recorded in Myocardial Ischaemia National Audit Project (MINAP), who had no previous evidence of MI in their General Practice Research Database (GPRD) or MINAP record were included. Patients under 18 years of age, not registered with GPRD at the time of MI, or with <1 year of standard follow-up before their MI were excluded. Data were provided by the "Cardiovascular Disease Research Linking Bespoke Cohorts and Electronic Records" (CALIBER) group at UCL. The primary exposure of interest was diagnosis of COPD (defined in GPRD) and the outcome death after MI. Survival analysis was done using Kaplan-Meier methods. Cox proportional hazards models were used to adjust for potential confounders (age and sex). Results 8065 individuals were included, 968 (12%) of whom had a physician diagnosis of COPD made either before the first MI or during the follow-up period. 87 patients died on the day of admission 10 (11.5%) of whom had COPD. The overall mortality rate was 160.2 deaths (95%CI 145.5 to 176.5) per 1000 person years in those with COPD compared to 99.4 deaths (95.2 to 103.9) per 1000 person years in those without COPD. After adjusting for confounding by sex and stratifying for age, survival was shorter after 1st MI in patients with COPD; HR 1.37 (1.23 to 1.52, p<0.001) in those with COPD compared to those without COPD (Abstract S96 figure 1). Survival was shorter in those (n=96) who exacerbated within 6 months of their 1st MI; HR 1.72 (1.13 to 2.60, p=0.01). Conclusions Survival is shorter after an "unanticipated" MI in patients with COPD and patients who exacerbate within 6 months of their MI have an even higher mortality rate. [ABSTRACT FROM AUTHOR]

The article discusses a study to determine whetherß blockers are associated with decreased mortality in patients with chronic obstructive pulmonary disease (COPD) having a first myocardial infarction. Patients with COPD with a first myocardial infarction from January 1, 2003 to December 31, 2008 was recorded. It indicates thatßblockers initiated upon admission for myocardial infarction were associated with substantial survival benefits.

Background: High job strain has been linked with cardiovascular outcomes. This study aimed to examine whether job strain is associated with angina pectoris symptoms among British and Finnish non-manual employees. Methods: Postal questionnaire survey data among 40-60-year-old employees of the British Whitehall II Study (n=4551, 27% women) and the Finnish Helsinki Health Study (n=7605, 83% women) cohort were analysed. Angina pectoris symptoms were the outcome in logistic regression analysis. Karasek's job strain was examined. Models were adjusted first for age, second for occupational class and finally for smoking, heavy drinking, physical inactivity, unhealthy food habits and obesity. Results: Angina pectoris symptoms were reported by 5% of women and 3% of men in Britain, and by 6% of women and 4% of men in Finland. High job strain was associated with angina pectoris symptoms among men in Britain (OR 2.08; CI 95% 1.07 to 4.02) and women in Finland (OR 1.90; CI 95% 1.36 to 2.63) independent of age, occupational class, and behavioural risk factors. However, similar associations between job strain and angina pectoris symptoms were not observed among men in Finland or women in Britain. Conclusion: The results yielded partial support for the association between job strain and angina pectoris symptoms across national contexts. [ABSTRACT FROM AUTHOR]

Discusses variation in the control of blood pressure in hypertensive patients from different ethnic groups. Difference in response to mono-therapy between Afro-Americans and whites; Control of blood pressure with calcium channel blockers in Afro-American Kenyan patients; Reasons provided for the variations observed in the control of blood pressure.