From effect size into number needed to treat.
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Humans↗
Biomedical subjects
L M Bouter
Publications and source records attributed to L M Bouter.
[The practice of systematic reviews. V. Heterogeneity between studies and subgroup analysis].
Meta-analysis comprises the analysis of the data of similar studies gathered in a systematic review. If the results of the studies differ (strongly), this is called heterogeneity. Possible causes of heterogeneity are: a wrong choice of type of measure of treatment effect, differences of methodological quality between studies, or real differences between studies. Heterogeneity between studies can be assessed by thorough examination of the differences between study characteristics in combination with a visual inspection of the degree of overlap of the confidence intervals of the estimates of effect of the different studies. By applying the random effects model for pooling, (non-systematic) heterogeneity between studies can be addressed. In case of heterogeneity between studies, sources of heterogeneity should be explored by means of subgroup analysis according to strict, present criteria. Subgroup analysis should address subgroups of patients within studies.
Confidence Intervals↗
[The practice of systematic reviews. IV. Pooling results from separate studies].
Meta-analysis comprises the analysis of the data gathered in a systematic review. Meta-analysis can be defined as the combination of pooling results of similar studies into one overall estimate of the effect on the one hand and the exploration of sources of heterogeneity between studies on the other. A general statistical model is available for pooling the estimates of various types of effect parameters. Pooling enables the estimation of the effect of an intervention or exposure as precisely as possible (with narrow confidence intervals) which allows detection of minor effects. The Mantel-Haenszel method is also an excellent method for pooling effect parameters of dichotomous outcomes. Pooling provides an efficient means of summarizing the available knowledge.
Data Interpretation, Statistical↗
[The practice of systematic reviews. III. Evaluation of methodological quality of research studies].
The methodological quality of the primary studies included in a systematic review may influence its results and final conclusions. Methodological quality may be defined in various ways. Partially because of this there are many different assessment lists. The most important dimension of quality is internal validity, defined as the confidence that the design, performance and report of a trial prevent or reduce systematic errors (bias) in the outcomes. For only a limited number of internal validity items a relationship with bias has been proven in empirical studies: concealment of randomisation and blinding of patients and outcome assessors. Preferably, quality should be assessed by at least 2 assessors independently. There is no consensus whether assessment should be done blinded for authors, journal, results and conclusions. Internal validity can be incorporated into statistical pooling in various ways: as a selection criterion, to be used as weight or to hierarchically order studies in a presentation. Well-designed comparative studies are needed to provide clearer guidelines for methodological assessment in the future.
Bias↗
[The practice of systematic reviews. II. Searching and selection of studies].
Structured searching and selection of studies is an important component of a systematic review. It is recommended to record the various steps in a protocol in advance. The thoroughness of the searching and selection will partially depend on the available resources, like manpower and funds. A search action should be based on an unequivocally formulated research or clinical question, that is operationalized into clear inclusion and exclusion criteria. The actual start of a search strategy is a search in preferably multiple databases like Medline and EMBASE-Excerpta Medica. Additional search actions can be performed in trial registers and printed indexes and by correspondence with experts and hand searching of journals. Storage of the search results in a bibliographic database is recommended. Various methodological problems may play a role in searching and selecting studies for a review: studies may selectively not be published, results are only partially presented in the publication, studies are selectively included in reference lists, and reviewers themselves may make systematic errors in the selection process.
Bias↗
Hyperproinsulinaemia in impaired glucose tolerance is associated with a delayed insulin response to glucose.
In subjects with impaired glucose tolerance hyperproinsulinaemia has been shown to be predictive for progression to Type II (non-insulin-dependent) diabetes mellitus. These findings are often interpreted as early indicators of an impaired beta-cell function. The aim of our study was to assess the potential determinants of hyperproinsulinaemia in subjects with impaired glucose tolerance. The study group consisted of 110 subjects, 45-74 years of age with mean 2 h plasma glucose concentrations between 8.6 and 11.1 mmol/l following two oral glucose tolerance tests. Subsequently, the hyperglycaemic clamp technique (10 mmol/l, with a priming infusion of 20% glucose solution, 150 mg/kg) was used to assess the beta-cell function (time needed to reach the insulin peak) and insulin sensitivity (M/I value: glucose metabolised divided by insulin response, 150-180 min). Results showed that the intact-proinsulin:insulin ratio increased with increasing time needed to reach the insulin peak (0.065, 0.079 and 0.101; time needed to reach the insulin peak < or = 5 min, 5 to 15 min, > 15 min; p < 0.05). The split-proinsulin:insulin ratio showed a similar association with the time needed to reach the insulin peak. These associations were independent of age, sex, body mass index and waist:hip ratio. In conclusion, this study shows that relative hyperproinsulinaemia is associated with an impaired beta-cell function in a study group of subjects with impaired glucose tolerance selected after two oral glucose tolerance tests.
Aged↗
Hyperglycaemia is associated with all-cause and cardiovascular mortality in the Hoorn population: the Hoorn Study.
AIMS/HYPOTHESIS: The degree of glycaemia has been shown to be associated with all-cause and cardiovascular mortality in diabetic subjects. Whether this association also exists in the general population is still controversial. We studied the predictive value of fasting plasma glucose, 2-hour post-load glucose and HbA1c in a population-based cohort of 2363 older (50-75 years) subjects, without known diabetes. METHODS: Relative risks (RR) of all-cause and cardiovascular mortality were estimated by Cox proportional hazards model, adjusting for age and sex, and additionally for known cardiovascular risk factors. RESULTS: During 8 years of follow-up, 185 subjects died; 98 of cardiovascular causes. Fasting plasma glucose was only predictive in the diabetic range, although the risks started to increase at about 6.1 mmol/l. Post-load glucose and HbA1c values were, even within the non-diabetic range, associated with an increased risk (p for linear trend < 0.05). These increased risks were mostly, but not completely, attributable to known cardiovascular risk factors. After exclusion of subjects with newly diagnosed diabetes or with pre-existent cardiovascular disease (n = 551), a 5.8 mmol/l increase of post-load glucose (corresponding to two standard deviations of the population distribution) was associated with a higher age-adjusted and sex-adjusted risk of all-cause (RR 2.24) and cardiovascular mortality (RR 3.40) (p < 0.05). After additional adjustment for known cardiovascular risk factors, these relative risks were still statistically significant, with values of 2.20 and 3.00 respectively (p < 0.05). CONCLUSION/INTERPRETATION: High glycaemic variables, especially 2-h post-load glucose concentrations and to a lesser extent HbA1c values, indicate a risk of all-cause and cardiovascular mortality in a general population without known diabetes.
Aged↗
Indirect costs of back pain in the Netherlands: a comparison of the human capital method with the friction cost method.
In this study we estimated the indirect costs of back pain in 1991 in The Netherlands on the basis of two approaches: the traditionally used human capital method and the more recently developed friction cost method. The indirect costs of illness were defined as the value of production losses of paid labour and related costs to society due to back pain. The results of this study in 1991 in The Netherlands show that the short-term indirect costs estimated by the human capital method were more than three times as high as the indirect costs estimated by the friction cost method (US$ 4.6 billion vs. USS 1.5 billion, respectively). The lower estimate of indirect costs when using the friction cost method is mainly due to the fact that in this method actual production losses are estimated during a relatively short friction period, which is defined as the period needed to restore the initial production level. In contrast with the human capital method, long-term absenteeism and disability do not induce additional costs when applying the friction cost method. Since the friction cost method takes into account that employees can be replaced, we believe that this method produces a more accurate estimate of indirect costs than the human capital method. Notwithstanding the resulting decrease in indirect costs of back pain, these costs are still impressive, representing 0.28% of the GNP in The Netherlands in 1991. As a consequence, but particularly stimulated by structural changes in the Dutch social security system, policies aimed at reducing indirect costs of back pain, increasingly concentrate on the development and evaluation of interventions early after the onset of disease. This is complemented, on the one hand, by the development of clinical guidelines for the management of back pain in primary care and, on the other hand, by governmental policies aimed at reintegration of chronically ill in the labour force.
Adult↗
Normohomocysteinaemia and vitamin-treated hyperhomocysteinaemia are associated with similar risks of cardiovascular events in patients with premature peripheral arterial occlusive disease. A prospective cohort study.
OBJECTIVES: Mild hyperhomocysteinaemia (HHC), fasting or after methionine loading, is associated with an increased risk and severity of atherosclerotic vascular disease. Post-methionine and fasting HHC are responsive to treatment with vitamin B, and folic acid. We performed a prospective cohort study amongst normohomocysteinaemic and vitamin-treated (vitamin B6, 250 mg plus folic acid, 5 mg daily) hyperhomocysteinaemic patients with premature peripheral arterial occlusive disease and assessed the incidence of cardiovascular events. DESIGN: We studied 273 consecutive patients with clinically manifest peripheral arterial occlusive disease with onset before the age of 56, 79 (28.9%) of whom had postmethionine HHC. Follow-up was obtained in 232 (85'%o) patients. At baseline, 70 (30')/) were hyperhomocysteinaemic after methionine loading and started treatment with vitamin B, and folic acid; 162 (70%) were normohomocysteinaemic (reference group). RESULTS: During the follow-up period (median 20, range 1-63 months), 48 (29.6%) and 23 (32.9%) of the normo- and the hyperhomocysteinaemic patients, respectively, had a new cardiovascular event. Most (75%) involved the peripheral arterial system. The crude incidence rate for any cardiovascular event was 0.16 (95% CI, 0.12-0.21) per person per year in the normohomocysteinaemic and 0.16 (95% CI, 0.09-0.22) per person per year in the hyperhomocysteinaemic group. Multivariate Cox regression analyses showed that higher plasma homocysteine levels were associated with an increased risk of new cardiovascular events in the normohomocysteinaemic patients (relative risk [RR] per 1 micromol L(-1), 1.17 [CI, 1.05-1.30] for fasting and 1.06 [CI, 1.01-1.12] for postmethionine levels), but not in the hyperhomocysteinaemic (vitamin-treated) patients. The adjusted RR for new cardiovascular events in the hyper- as compared to the normohomocysteinaemic patients was 0.76 (CI, 0.33-1.74). CONCLUSIONS: These data are consistent with a protective effect of treatment with vitamin B6 and folic acid in patients with premature peripheral arterial occlusive disease and postmethionine HHC. Double-blind randomized trials are necessary to confirm this.
Adult↗
Education and incident Alzheimer's disease: a biased association due to selective attrition and use of a two-step diagnostic procedure?
BACKGROUND: It is still not clear whether a low level of education increases the risk of developing Alzheimer's disease (AD). Two common problems in cohort studies involving an elderly population and a two-step diagnostic procedure are the loss to follow-up without data on the presence of AD, and the fact that, in general, people with higher levels of education perform better on traditional cognitive tests, such as the Mini-Mental State Examination (MMSE). Both phenomena may lead to misclassification, resulting in a biased association between level of education and AD. This study investigated to what extent these selection mechanisms may influence this association. METHODS: In the community-based Amsterdam Study of the Elderly (AMSTEL) a cohort at risk for AD was selected of 3778 people aged 65-84 years. Level of education was expressed in two categories: low (primary education or less) versus high (partial secondary education to completed university education). At follow-up, a subsample of elderly people was selected for further diagnostic evaluation, using a memory test in addition to the MMSE. Clinical diagnoses of AD were made according to DSM-IV (Diagnostic and Statistical Manual of Mental Disorders) criteria. To examine the extent to which loss to follow-up may have affected the results, a sensitivity analysis was performed comparing two extreme possibilities. Furthermore, to examine to what extent use of the MMSE only may have affected the results, the observed odds ratio (OR) was compared with the OR based on only those AD patients who were selected for diagnostics with the MMSE alone. RESULTS: After an average of 3.2 years, 77 people had developed AD. Multivariate logistic regression analyses indicated that a low level of education was associated with incident AD (OR adjusted for age and sex 2.09; 95% CI: 1.29-3.38). The results of the sensitivity analysis still indicated that a low level of education was associated with incident AD. Screening with only the MMSE led to a higher OR than the one observed. CONCLUSION: Selective attrition and use of cognitive screening tests that are associated with educational level may influence the strength of the association between a low level of education and incident AD; however, it appears that these influences cannot completely explain this association.
Aged↗
Upper respiratory tract infection, heterologous immunisation and meningococcal disease.
To test the hypothesis that an episode of upper respiratory tract infection or heterologous immunisation is a predisposing factor for the occurrence of meningococcal disease, data from 377 cases of meningococcal disease and their household contacts (n = 1124) were analysed by conditional logistic regression analysis with stratification for household. The odds ratio for a recent upper respiratory tract infection for patients versus household contacts, adjusted for age and the presence of an underlying predisposing disease, was 2.8 and that for recent heterologous immunisation 1.0. These results support previous observations regarding the association between a preceding upper respiratory tract infection and the occurrence of meningococcal disease; however, no association was found between preceding heterologous immunisation and meningococcal disease. Therefore, increased alertness after heterologous immunisation does not seem warranted.
Adolescent↗
Diagnostic classification of shoulder disorders: interobserver agreement and determinants of disagreement.
OBJECTIVES: To assess the interobserver agreement on the diagnostic classification of shoulder disorders, based on history taking and physical examination, and to identify the determinants of diagnostic disagreement. METHODS: Consecutive eligible patients with shoulder pain were recruited in various health care settings in the Netherlands. After history taking, two physiotherapists independently performed a physical examination and subsequently the shoulder complaints were classified into one of six diagnostic categories: capsular syndrome (for example, capsulitis, arthritis), acute bursitis, acromioclavicular syndrome, subacromial syndrome (for example, tendinitis, chronic bursitis), rest group (for example, unclear clinical picture, extrinsic causes) and mixed clinical picture. To quantify the interobserver agreement Cohen's kappa was calculated. Multivariate logistic regression analysis was applied to determine which clinical characteristics were determinants of diagnostic disagreement. RESULTS: The study population consisted of 201 patients with varying severity and duration of complaints. The kappa for the classification of shoulder disorders was 0.45 (95% confidence intervals (CI) 0.37, 0.54). Diagnostic disagreement was associated with bilateral involvement (odds ratio (OR) 1.9; 95% CI 1.0, 3.7), chronic complaints (OR 2.0; 95% CI 1.1, 3.7), and severe pain (OR 2.7; 95% CI 1.3, 5.3). CONCLUSIONS: Only moderate agreement was found on the classification of shoulder disorders, which implies that differentiation between the various categories of shoulder disorders is complicated. Especially patients with high pain severity, chronic complaints and bilateral involvement represent a diagnostic challenge for clinicians. As diagnostic classification is a guide for treatment decisions, unsatisfactory reproducibility might affect treatment outcome. To improve the reproducibility, more insight into the reproducibility of clinical findings and the value of additional diagnostic procedures is needed.
Acromioclavicular Joint↗
No effect of bipolar interferential electrotherapy and pulsed ultrasound for soft tissue shoulder disorders: a randomised controlled trial.
OBJECTIVE: To assess the efficacy of bipolar interferential electrotherapy (ET) and pulsed ultrasound (US) as adjuvants to exercise therapy for soft tissue shoulder disorders (SD). METHODS: Randomised placebo controlled trial with a two by two factorial design plus an additional control group in 17 primary care physiotherapy practices in the south of the Netherlands. Patients with shoulder pain and/or restricted shoulder mobility, because of a soft tissue impairment without underlying specific or generalised condition, were enrolled if they had not recovered after six sessions of exercise therapy in two weeks. They were randomised to receive (1) active ET plus active US; (2) active ET plus dummy US; (3) dummy ET plus active US; (4) dummy ET plus dummy US; or (5) no adjuvants. Additionally, they received a maximum of 12 sessions of exercise therapy in six weeks. Measurements at baseline, 6 weeks and 3, 6, 9, and 12 months later were blinded for treatment. OUTCOME MEASURES: recovery, functional status, chief complaint, pain, clinical status, and range of motion. RESULTS: After written informed consent 180 patients were randomised: both the active treatments were given to 73 patients, both the dummy treatments to 72 patients, and 35 patients received no adjuvants. Prognosis of groups appeared similar at baseline. Blinding was successfully maintained. At six weeks seven patients (20%) without adjuvants reported very large improvement (including complete recovery), 17 (23%) and 16 (22%) with active and dummy ET, and 19 (26%) and 14 (19%) with active and dummy US. These proportions increased to about 40% at three months, but remained virtually stable thereafter. Up to 12 months follow up the 95% CI for differences between groups for all outcomes include zero. CONCLUSION: Neither ET nor US prove to be effective as adjuvants to exercise therapy for soft tissue SD.
Adult↗
Microalbuminuria and peripheral arterial disease are independent predictors of cardiovascular and all-cause mortality, especially among hypertensive subjects: five-year follow-up of the Hoorn Study.
Microalbuminuria (MA) is associated with increased cardiovascular and all-cause mortality. It has been proposed that MA reflects generalized atherosclerosis and may thus predict mortality. To investigate this hypothesis, we studied the associations between, on the one hand, MA and peripheral arterial disease (PAD), a generally accepted marker of generalized atherosclerosis, and, on the other hand, cardiovascular and all-cause mortality in an age-, sex-, and glucose tolerance-stratified sample (n=631) of a population-based cohort aged 50 to 75 years followed prospectively for 5 years. At baseline, the albumin-to-creatinine ratio (ACR) was measured in an overnight spot urine sample; MA was defined as ACR >2.0 mg/mmol. PAD was defined as an ankle-brachial pressure index below 0.90 and/or a history of a peripheral arterial bypass or amputation. After 5 years of follow-up, 58 subjects had died (24 of cardiovascular causes). Both MA and PAD were associated with a 4-fold increase in cardiovascular mortality. After adjusting for age, sex, diabetes mellitus, hypertension, levels of total and HDL-cholesterol and triglyceride, body mass index, smoking habits, and preexistent ischemic heart disease, the relative risks (RR) (95% confidence intervals) were 3.2 (1.3 to 8.1) for MA and 2.4 (0.9 to 6.1) for PAD. When both MA and PAD were included in the multivariate analysis, the RRs were 2.9 (1.1 to 7.3) for MA and 2.0 (0.7 to 5.7) for PAD. MA and PAD were both associated with an about 2-fold increase in all-cause mortality. The RRs of all-cause mortality associated with MA and PAD were about 4 times higher among hypertensive than among normotensive subjects. We conclude that both MA and PAD are associated with an increased risk of cardiovascular mortality. MA and PAD are mutually independent risk indicators. The associations of MA and PAD with all-cause mortality are somewhat weaker. They are more pronounced in the presence of hypertension than in its absence. These data suggest that MA affects mortality risk through a mechanism different from generalized atherosclerosis.
Age Factors↗
Association between memory complaints and incident Alzheimer's disease in elderly people with normal baseline cognition.
OBJECTIVE: Results of previous studies suggest that memory complaints may predict cognitive decline and dementia among elderly people in whom cognitive impairment is already apparent. However, cognitive decline is often a gradual process, and elderly people may notice that their memory deteriorates before mental status tests are able to detect any change in cognitive functioning. Therefore, the authors hypothesized that memory complaints would predict incident Alzheimer's disease in elderly subjects with no signs of cognitive impairment. METHOD: In the community-based Amsterdam Study of the Elderly, a sample of 3,778 nondemented persons, 65 to 84 years old, was selected and divided into two cognitive categories: normal (Mini-Mental State scores of 26-30) and borderline and impaired (Mini-Mental State scores less than 26). At baseline, the presence or absence of memory complaints was assessed. At follow-up, incident cases of Alzheimer's disease were diagnosed in a two-step procedure. RESULTS: After an average of 3.2 years, 2,169 persons were reevaluated, of whom 77 had incident Alzheimer's disease. Multivariate logistic regression analyses showed that memory complaints were associated with incident Alzheimer's disease in subjects with normal baseline cognition but not in subjects with impaired baseline cognition. CONCLUSIONS: The findings of this study suggest that memory complaints are a relatively strong predictor of incident Alzheimer's disease in older persons in whom cognitive impairment is not yet apparent. Furthermore, they suggest that older persons may be aware of a decline in cognition at a time when mental status tests are still unable to detect a decline from premorbid functioning.
Aged↗
Leptin and variables of body adiposity, energy balance, and insulin resistance in a population-based study. The Hoorn Study.
OBJECTIVE: Leptin is thought to play a key role in the control of body weight. There is a complex interrelationship between leptin and insulin or insulin resistance, but it is unknown how leptin is regulated. We therefore explored, in a large population-based study of 2,484 Caucasian subjects aged 50-74 years, the relationship between leptin and variables of body adiposity, energy balance, and insulin resistance. RESEARCH DESIGN AND METHODS: Leptin was measured by means of a radioimmunoassay. Multiple linear regression analyses were performed with leptin as dependent variable and age, sex, BMI, waist circumference, daily energy intake, physical activity, smoking, hypertension, fasting triglyceride concentrations, HDL cholesterol, fasting plasma glucose, and fasting plasma insulin concentrations as independent variables (determinants) RESULTS: Leptin concentrations were found to be four times higher in women than in men. Effect modification between sex and potential determinants was expected, and the analyses were performed separately for women and men. BMI was the strongest determinant of leptin in women and waist circumference the strongest determinant in men. BMI, waist circumference, insulin, and triglyceride concentrations were independently and significantly (P < 0.05) associated with leptin, while inverse associations were shown for smoking and daily energy intake (borderline significance). CONCLUSIONS: This study confirms the relationship between insulin and leptin and, in addition, suggests a relationship between triglyceride concentrations and leptin independent of sex, BMI, waist circumference, and insulin.
Adipose Tissue↗
Effectiveness of corticosteroid injections versus physiotherapy for treatment of painful stiff shoulder in primary care: randomised trial.
OBJECTIVE: To compare the effectiveness of corticosteroid injections with physiotherapy for the treatment of painful stiff shoulder. DESIGN: Randomised trial. SETTING: 40 general practices. SUBJECTS: 109 patients consulting general practitioners for shoulder pain were enrolled in the trial. INTERVENTIONS: Patients were randomly allocated to 6 weeks of treatment either with corticosteroid injections (53) or physiotherapy (56). MAIN OUTCOME MEASURES: Outcome assessments were carried out 3, 7, 13, 26, and 52 weeks after randomisation; some of the assessments were done by an observer blind to treatment allocation. Primary outcome measures were the success of treatment as measured by scores on scales measuring improvement in the main complaint and pain, and improvement in scores on a scale measuring shoulder disability. RESULTS: At 7 weeks 40 (77%) out of 52 patients treated with injections were considered to be treatment successes compared with 26 (46%) out of 56 treated with physiotherapy (difference between groups 31%, 95% confidence interval 14% to 48%). The difference in improvement favoured those treated with corticosteroids in nearly all outcome measures; these differences were statistically significant. At 26 and 52 weeks differences between the groups were comparatively small. Adverse reactions were generally mild. However, among women receiving treatment with corticosteroids adverse reactions were more troublesome: facial flushing was reported by 9 women and irregular menstrual bleeding by 6, 2 of whom were postmenopausal. CONCLUSIONS: The beneficial effects of corticosteroid injections administered by general practitioners for treatment of painful stiff shoulder are superior to those of physiotherapy. The differences between the intervention groups were mainly the result of the comparatively faster relief of symptoms that occurred in patients treated with injections. Adverse reactions were generally mild but doctors should be aware of the potential side effects of injections of triamcinolone, particularly in women.
Adult↗
Methodologic issues in low back pain research in primary care.
STUDY DESIGN: Narrative review and discussion of the selected literature. OBJECTIVES: To discuss some important methodologic challenges in low back pain research in primary care. SUMMARY OF BACKGROUND DATA: Many methodologic problems must be confronted when conducting low back pain research. Some of these problems are back pain specific or specific to the primary care setting. METHODS: Methodologic problems related to four research issues will be discussed: study designs, definition of low back pain, determinants of low back pain, and outcome assessment. RESULTS: Two fundamentally different study designs are frequently used in low back pain research, namely observational studies and experimental studies. The definition of low back pain is typically restricted to a highly variables self-reported symptom, the sensation of pain in the back. There clearly is a need for an evidence-based classification system for low back pain. Because a tenable theoretical framework is lacking, it is difficult to know which determinants of low back pain should be quantified. Low back pain studies focus usually on health-related quality-of-life outcome parameters. The identification of the minimum clinically relevant changes for the most important outcome instruments needs further consideration. CONCLUSIONS: In years to come, low back pain researchers are challenged to overcome some of these (and other) problems to enhance the quality of low back pain research in primary care.
Clinical Trials as Topic↗