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Biomedical subjects

A D Oxman

Publications and source records attributed to A D Oxman.

At least 19 recordsLinked to original sources
PubMed2006

Methods of consumer involvement in developing healthcare policy and research, clinical practice guidelines and patient information material.

BACKGROUND: The importance of consumer involvement in health care is widely recognised. Consumers can be involved in developing healthcare policy and research, clinical practice guidelines and patient information material, through consultations to elicit their views or through collaborative processes. Consultations can be single events, or repeated events, large or small scale. They can involve individuals or groups of consumers to allow debate; the groups may be convened especially for the consultation or be established consumer organisations. They can be organised in different forums and through different media. We anticipated finding few comparative evaluations that reliably evaluated the effects of consumer involvement. OBJECTIVES: To assess the effects of consumer involvement and compare different methods of involvement in developing healthcare policy and research, clinical practice guidelines, and patient information material. SEARCH STRATEGY: We searched: the Cochrane Consumers and Communication Review Group's Specialised Register (4 May 2006); the Cochrane Controlled Trials Register (CENTRAL) (The Cochrane Library, Issue 1 2006), MEDLINE (1966 to January Week 2 2006); EMBASE (1980 to Week 03 2006); CINAHL (1982 to December Week 2 2005), PsycINFO (1806 to January Week 3 2006); Sociological Abstracts (1952 to 24 January 2006); and SIGLE (System for Information on Grey Literature in Europe) (1980 to 2003/1). We scanned reference lists from relevant articles and contacted authors. SELECTION CRITERIA: Randomised and quasi-randomised trials, interrupted time series analyses, and controlled before-after studies assessing methods for involving consumers in developing healthcare policy and research, clinical practice guidelines or patient information material. The outcome measures were: participation or response rates of consumers; consumer views elicited; consumer influence on decisions, healthcare outcomes or resource utilisation; consumers' or professionals' satisfaction with the involvement process or resulting products; impact on the participating consumers; costs. DATA COLLECTION AND ANALYSIS: Two review authors independently selected trials for inclusion, assessed their quality and extracted data. We contacted study authors for clarification and to seek missing data. We presented results in a narrative summary and pooled data as appropriate. MAIN RESULTS: Five randomised controlled trials of moderate or low methodological quality involving 1031 participants were included. There is moderate quality evidence that involving consumers in the development of patient information material results in material that is more relevant, readable and understandable to patients, without affecting their anxiety. This 'consumer-informed' material can also improve patients' knowledge. There is low quality evidence that using consumer interviewers instead of staff interviewers in satisfaction surveys can have a small influence on the survey results. There is very low quality evidence of telephone discussions and face-to-face group meetings engaging consumers better than mailed surveys in order to set priorities for community health goals, and resulting in different priorities being set for these goals. AUTHORS' CONCLUSIONS: There is little evidence from comparative studies of the effects of consumer involvement in healthcare decisions at the population level. The studies included in this review demonstrate that randomised controlled trials are feasible for providing evidence about the effects of consulting consumers to inform these decisions.

Community Participation↗
PubMed2006

Audit and feedback: effects on professional practice and health care outcomes.

BACKGROUND: Audit and feedback continues to be widely used as a strategy to improve professional practice. It appears logical that healthcare professionals would be prompted to modify their practice if given feedback that their clinical practice was inconsistent with that of their peers or accepted guidelines. Yet, audit and feedback has not consistently been found to be effective. OBJECTIVES: To assess the effects of audit and feedback on the practice of healthcare professionals and patient outcomes. SEARCH STRATEGY: We searched the Cochrane Effective Practice and Organisation of Care Group's register and pending file up to January 2004. SELECTION CRITERIA: Randomised trials of audit and feedback (defined as any summary of clinical performance over a specified period of time) that reported objectively measured professional practice in a healthcare setting or healthcare outcomes. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed study quality. Quantitative (meta-regression), visual and qualitative analyses were undertaken. For each comparison we calculated the risk difference (RD) and risk ratio (RR), adjusted for baseline compliance when possible, for dichotomous outcomes and the percentage and the percent change relative to the control group average after the intervention, adjusted for baseline performance when possible, for continuous outcomes. We investigated the following factors as possible explanations for the variation in the effectiveness of interventions across comparisons: the type of intervention (audit and feedback alone, audit and feedback with educational meetings, or multifaceted interventions that included audit and feedback), the intensity of the audit and feedback, the complexity of the targeted behaviour, the seriousness of the outcome, baseline compliance and study quality. MAIN RESULTS: Thirty new studies were added to this update, and a total of 118 studies are included. In the primary analysis 88 comparisons from 72 studies were included that compared any intervention in which audit and feedback is a component compared to no intervention. For dichotomous outcomes the adjusted risk difference of compliance with desired practice varied from - 0.16 (a 16 % absolute decrease in compliance) to 0.70 (a 70% increase in compliance) (median = 0.05, inter-quartile range = 0.03 to 0.11) and the adjusted risk ratio varied from 0.71 to 18.3 (median = 1.08, inter-quartile range = 0.99 to 1.30). For continuous outcomes the adjusted percent change relative to control varied from -0.10 (a 10 % absolute decrease in compliance) to 0.68 (a 68% increase in compliance) (median = 0.16, inter-quartile range = 0.05 to 0.37). Low baseline compliance with recommended practice and higher intensity of audit and feedback were associated with larger adjusted risk ratios (greater effectiveness) across studies. AUTHORS' CONCLUSIONS: Audit and feedback can be effective in improving professional practice. When it is effective, the effects are generally small to moderate. The relative effectiveness of audit and feedback is likely to be greater when baseline adherence to recommended practice is low and when feedback is delivered more intensively.

Education, Medical, Continuing↗
PubMed2006

Pharmaceutical policies: effects of reference pricing, other pricing, and purchasing policies.

BACKGROUND: Pharmaceuticals can be important for people's health. At the same time drugs are major components of health care costs. Pharmaceutical pricing and purchasing policies are used to determine or affect the prices that are paid for drugs. Examples are price controls, maximum prices, price negotiations, reference pricing, index pricing and volume-based pricing policies. The essence of reference pricing is to establish a maximum level of reimbursement for a group of drugs assumed to be therapeutically equivalent. OBJECTIVES: To determine the effects of pharmaceutical pricing and purchasing policies on drug use, healthcare utilisation, health outcomes and costs (expenditures). SEARCH STRATEGY: We searched the following databases and web sites: Effective Practice and Organisation of Care Group Register (date of last search: 22/08/03), Cochrane Central Register of Controlled Trials (15/10/03), MEDLINE (07/09/05), EMBASE (07/09/05), ISI Web of Science (08/09/05), CSA Worldwide Political Science Abstracts (21/10/03), EconLit (23/10/03), SIGLE (12/11/03), INRUD (21/11/03), PAIS International (23/03/04), International Political Science Abstracts (09/01/04), NHS EED (20/02/04), PubMed (25/02/04), NTIS (03/03/04), IPA (22/04/04), OECD Publications & Documents (30/08/05), SourceOECD (30/08/05), World Bank Documents & Reports (30/08/05), World Bank e-Library (04/05/05), JOLIS (22/08/05), Global Jolis (22/08/05 and 23/08/05), WHOLIS (29/08/05). SELECTION CRITERIA: Policies in this review were defined as laws, rules, financial and administrative orders made by governments, non-government organisations or private insurers. To be included a study had to include an objective measure of at least one of the following outcomes: drug use, healthcare utilisation, health outcomes, and costs (expenditures); the study must be a randomised controlled trial, non-randomised controlled trial, interrupted time series analysis, repeated measures study or controlled before-after study of a pharmaceutical pricing or purchasing policy for a large jurisdiction or system of care. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed study limitations. Quantitative analysis of time series data, for studies with sufficient data, and qualitative analyses were undertaken. MAIN RESULTS: We included 10 studies of reference pricing and one study of index pricing. Most of the reference pricing studies were for senior citizens in British Columbia, Canada. The use (dispensing) of reference drugs increased in five studies, between 60% and 196% immediately after introduction of reference drug pricing, whereas the use of cost sharing drugs decreased by between 19% and 42% in four studies. In three studies the reference drug group expenditures decreased (range 19% - 50%), whereas in the fourth study the expenditures increased by 5% in the short term. The results after six months of reference pricing do not show any clear pattern in relationship to the immediate effects. We found no evidence of adverse effects on health and no clear evidence of increased health care utilisation. For index pricing the evidence was much more limited than for reference drug pricing. A small reduction in drug prices was found. AUTHORS' CONCLUSIONS: We found relatively few studies of pricing policies. The majority of the studies dealt with reference pricing. They had few methodological limitations. Based on the evidence in this review, mostly from senior citizens in British Columbia, Canada, reference drug pricing can reduce third party drug expenditures by inducing a shift in drug use towards less expensive drugs. We found no evidence of adverse effects on health and no clear evidence of increased health care utilisation. The analysis and reporting of the effects on patient drug expenditures were limited in the included studies and administration costs were not reported.

Cost Control↗
PubMed2003

The unbearable lightness of healthcare policy making: a description of a process aimed at giving it some weight.

OBJECTIVES: To investigate whether a structured process to involve policy makers in designing a research project on a return to work insurance policy would yield evidence that was relevant, useful, and used in policy decisions. STUDY DESIGN: Case study. SETTING: Norway. PARTICIPANTS: Two researchers from the National Institute of Public Health and four representatives from respectively the National Insurance Administration, Norwegian Confederation of Trade Unions, Confederation of Norwegian Business and Industry, and Norwegian Medical Association. INTERVENTION: Structured discussions of the research, including the objectives, interventions, design, and interpretation of the results. RESULTS: The participants succeeded in designing and completing a cluster randomised controlled trial through the participatory process. Intermediary results from the trial have been used in practical planning within the National Insurance Administration, but there are few indications that the main results of the trial have been used. CONCLUSIONS: This approach of involving policy makers in the research planning process when political or organisational values are at stake did not succeed in this case. The salient explanations for this are conflicting interests of the organisations involved in the process and the research findings were in conflict with those interests.

Attitude of Health Personnel↗
PubMed2003

Systematic reviews of the effectiveness of quality improvement strategies and programmes.

Systematic reviews provide the best evidence on the effectiveness of healthcare interventions including quality improvement strategies. The methods of systematic review of individual patient randomised trials of healthcare interventions are well developed. We discuss methodological and practice issues that need to be considered when undertaking systematic reviews of quality improvement strategies including developing a review protocol, identifying and screening evidence sources, quality assessment and data abstraction, analytical methods, reporting systematic reviews, and appraising systematic reviews. This paper builds on our experiences within the Cochrane Effective Practice and Organisation of Care (EPOC) review group.

Canada↗
PubMed2001

Continuing education meetings and workshops: effects on professional practice and health care outcomes.

BACKGROUND: Educational meetings and printed educational materials are the two most common types of continuing education for health professionals. An important aim of continuing education is to improve professional practice so that patients can receive improved health care. OBJECTIVES: To assess the effects of educational meetings on professional practice and health care outcomes. SEARCH STRATEGY: We searched the Cochrane Effective Practice and Organisation of Care Group specialised register, MEDLINE (from 1966), the Research and Development Resource Base in Continuing Medical Education in January 1999 and reference lists of articles. SELECTION CRITERIA: Randomised trials or well designed quasi-experimental studies examining the effect of continuing education meetings (including lectures, workshops, and courses) on the clinical practice of health professionals or health care outcomes. DATA COLLECTION AND ANALYSIS: Two reviewers independently applied inclusion criteria, assessed the quality of each study, and extracted study data. We attempted to collect missing data from investigators. We conducted both qualitative and quantitative analyses. MAIN RESULTS: Thirty-two studies were included with a total of 36 comparisons. The studies involved from 13 to 411 health professionals (total N= 2995) and were judged to be of moderate or high quality, although methods were generally poorly reported. There was substantial variation in the complexity of the targeted behaviours, baseline compliance, the characteristics of the interventions and the results. The heterogeneity of the results was best explained by differences in the interventions. For 10 comparisons of interactive workshops, there were moderate or moderately large effects in six (all of which were statistically significant) and small effects in four (one of which was statistically significant). For interventions that combined workshops and didactic presentations, there were moderate or moderately large effects in 12 comparisons (eleven of which were statistically significant) and small effects in seven comparisons (one of which was statistically significant). In seven comparisons of didactic presentations, there were no statistically significant effects, with the exception of one out of four outcome measures in one study. REVIEWER'S CONCLUSIONS: Interactive workshops can result in moderately large changes in professional practice. Didactic sessions alone are unlikely to change professional practice.

Congresses as Topic↗
PubMed2000

[Guidelines for diagnosis and treatment of sore throat].

BACKGROUND: Available guidelines for the diagnosis and treatment of sore throat give conflicting recommendations. Our aim was to develop evidence-based guidelines. MATERIAL AND METHODS: We searched The Cochrane Library, Medline and other sources for systematic reviews and other evidence that met explicit inclusion criteria for all of the relevant options and outcomes we identified. The validity of included studies was assessed. Draft recommendations based on assessment of this evidence were widely circulated and discussed in focus groups with patients and physician assistants. RESULTS: Throat infections are self-limiting and complications rare. Penicillin shortens the duration of symptoms in tonsillitis caused by beta-haemolytic streptococci and reduces the risk of complications. Penicillin has adverse effects and increases the risk of reinfections. Patients with sore throat should usually be treated without antibiotics. Visiting a physician is normally unnecessary. Antibiotics should be considered in serious cases or if the patient prefers this, but should only be prescribed for throat infections caused by beta-haemolytic streptococci. The diagnosis should be based on clinical criteria and a rapid antigen test in cases of doubt. INTERPRETATION: Benefits of antibiotics must be weighed against harms. Patients should be given good information and involved in decision/making if they want antibiotics.

Anti-Bacterial Agents↗
PubMed2000

[Guidelines for diagnosis and treatment of acute urinary tract problems in women].

BACKGROUND: Available guidelines for the management of symptoms of lower urinary tract infections (UTI) in women give conflicting recommendations. MATERIAL AND METHODS: We searched The Cochrane Library, Medline and other sources for evidence that met explicit inclusion criteria for the relevant options and outcomes identified. The validity of included studies was assessed. Draft recommendations were widely circulated and discussed in focus groups with patients and physician assistants. RESULTS: The probability that a woman with dysuria or frequency has bacteriuria, is 80%. The probability of UTI given a negative result of a dipstick test is 50%. Evidence suggests that antibiotics will rapidly relieve symptoms, but there are limited data from placebo-controlled randomised trials. Population based studies show that many women do not visit physicians for symptoms of UTI. Women with symptoms of UTI can be treated with antibiotics without examination of the urine. Women with earlier episodes of UTI can be offered treatment by telephone. Antibiotics for three days is sufficient based on eradication of bacteriuria. Women should be seen by a physician if the symptoms are atypical. INTERPRETATION: Implementing these guidelines could result in better service to women with UTIs. More evidence about the effects of antibiotics and other treatments is needed.

Anti-Bacterial Agents↗
PubMed2000

[Guidelines for diagnosis and treatment of sore throat].

BACKGROUND: Available guidelines for the diagnosis and treatment of sore throat give conflicting recommendations. Our aim was to develop evidence-based guidelines. MATERIAL AND METHODS: We searched The Cochrane Library, Medline and other sources for systematic reviews and other evidence that met explicit inclusion criteria for all of the relevant options and outcomes we identified. The validity of included studies was assessed. Draft recommendations based on assessment of this evidence were widely circulated and discussed in focus groups with patients and physician assistants. RESULTS: Throat infections are self-limiting and complications rare. Penicillin shortens the duration of symptoms in tonsillitis caused by beta-haemolytic streptococci and reduces the risk of complications. Penicillin has adverse effects and increases the risk of reinfections. Patients with sore throat should usually be treated without antibiotics. Visiting a physician is normally unnecessary. Antibiotics should be considered in serious cases or if the patient prefers this, but should only be prescribed for throat infections caused by beta-haemolytic streptococci. The diagnosis should be based on clinical criteria and a rapid antigen test in cases of doubt. INTERPRETATION: Benefits of antibiotics must be weighed against harms. Patients should be given good information and involved in decision-making if they want antibiotics.

Anti-Bacterial Agents↗
PubMed2000

Local opinion leaders: effects on professional practice and health care outcomes.

BACKGROUND: Both the theory of diffusion of innovations and the social influences model of behaviour change suggest that using local opinion leaders to transmit norms and model appropriate behaviour may improve health professional practice. OBJECTIVES: To assess the effects using local opinion leaders on the practice of health professionals or patient outcomes. SEARCH STRATEGY: We searched MEDLINE to May 1998, the Research and Development Resource Base in Continuing Medical Education, and reference lists of related systematic reviews and articles. SELECTION CRITERIA: Randomised trials of the use of local opinion leaders (defined as health professionals nominated by their colleagues as being educationally influential). The participants were health care professionals responsible for patient care. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed study quality. MAIN RESULTS: Eight studies were included involving more than 296 health professionals. A variety of patient problems were targeted, including acute myocardial infarction, cancer pain, osteoarthritis, rheumatoid arthritis, chronic lung disease, vaginal birth after caesarean section, labour and delivery, and urinary catheter care. Six of seven trials that measured health professional practice demonstrated some improvement for at least one outcome variable, and in two trials, the results were statistically significant and clinically important. In three trials that measured patient outcomes, only one achieved an impact upon practice that was of practical importance: local opinion leaders were effective in improving the rate of vaginal birth after previous caesarean section. REVIEWER'S CONCLUSIONS: Using local opinion leaders results in mixed effects on professional practice. However, it is not always clear what local opinion leaders do and replicable descriptions are needed. Further research is required to determine if opinion leaders can be identified and in which circumstances they are likely to influence the practice of their peers.

Health Services Research↗
PubMed2000

Audit and feedback: effects on professional practice and health care outcomes.

BACKGROUND: Audit and feedback has been identified as having the potential to change the practice of health care professionals. OBJECTIVES: To assess the effects of audit and feedback on the practice of health professionals and patient outcomes. SEARCH STRATEGY: We searched MEDLINE up to June 1997, the Research and Development Resource Base in Continuing Medical Education, and reference lists of related systematic reviews and articles. SELECTION CRITERIA: Randomised trials of audit and feedback (defined as any summary of clinical performance of health care over a specified period of time). The participants were health care professionals responsible for patient care. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed study quality. MAIN RESULTS: Thirty-seven studies were included, involving more than 4977 physicians. The reporting of study methods was inadequate for almost all studies. In 31 out of 37 studies the randomisation process could not be determined. Information regarding data analysis was also lacking. For example, power calculations were not mentioned in 27 out of 37 studies. A variety of behaviours were targeted including the reduction of diagnostic test ordering, prescribing practices, preventive care, and the general management of a problem, for example hypertension. Twenty-eight studies measured physician performance, one study targeted patient outcomes in diabetes and the remaining eight studies measured both physician performance and patient outcomes. The relative percentage differences ranged from -16% to 152%. The clinical importance of the changes was not always clear. REVIEWER'S CONCLUSIONS: Audit and feedback can sometimes be effective in improving the practice of health care professionals, in particular prescribing and diagnostic test ordering. When it is effective, the effects appear to be small to moderate but potentially worthwhile. Those attempting to enhance professional behaviour should not rely solely on this approach.

Education, Medical, Continuing↗
PubMed2000

Audit and feedback versus alternative strategies: effects on professional practice and health care outcomes.

BACKGROUND: Audit and feedback has been identified as having the potential to change the practice of health care professionals. OBJECTIVES: To assess the effects of audit and feedback compared with other interventions in changing health professional practice and to assess whether the effectiveness of audit and feedback can be improved by modifying how it is done. SEARCH STRATEGY: We searched MEDLINE up to June 1997, the Research and Development Resource Base in Continuing Medical Education, and reference lists of related systematic reviews and articles. SELECTION CRITERIA: Randomised trials of audit and feedback (defined as any summary of clinical performance of health care over a specified period of time) compared with other interventions. The participants were health care providers responsible for patient care. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed study quality. MAIN RESULTS: Twelve studies were included involving more than 2194 physicians. Seven trials with direct comparisons were included. The targeted behaviours were the management of low haemoglobin, the delivery of preventive care services (two studies), the management of high cholesterol, the performance of cervical smears, and the ordering of diagnostic tests (two studies). From the results of four trials, there is little evidence of a measurable effect of adding a complementary intervention such as a local consensus process to audit and feedback compared to audit and feedback alone. Two of three trials that compared audit and feedback to reminders reported that reminders were more effective in improving the delivery of some preventive services. REVIEWER'S CONCLUSIONS: It is not possible to recommend a complementary intervention to enhance the effectiveness of audit and feedback. Reminders might be more effective than audit and feedback to improve the delivery of some preventive services but the results are not striking. Few trials have investigated the effect of varying different characteristics of the audit and feedback process. Consideration should be given to testing the effects of modifying important characteristics such as the content, source, timing, recipient and format.

Education, Medical, Continuing↗
PubMed2000

Educational outreach visits: effects on professional practice and health care outcomes.

BACKGROUND: Outreach visits have been identified as an intervention that may improve the practice of health care professionals, in particular prescribing. This type of 'face to face' visit has been referred to as university-based educational detailing, public interest detailing, and academic detailing. OBJECTIVES: To assess the effects of outreach visits on improving health professional practice or patient outcomes. SEARCH STRATEGY: We searched MEDLINE up to March 1997, the Research and Development Resource Base in Continuing Medical Education, and reference lists of related systematic reviews and articles. SELECTION CRITERIA: Randomised trials of outreach visits (defined as a personal visit by a trained person to a health care provider in his or her own setting). The participants were health care professionals. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed study quality. MAIN RESULTS: Eighteen studies were included involving more than 1896 physicians. All of the outreach visit interventions consisted of several components, including written materials and conferences. Reminders or audit and feedback complemented some visits. In 13 studies, the targeted behaviours were prescribing practices. In three studies, the behaviours were preventive services, including counselling for smoking cessation. In two studies, the outreach visits were directed toward improving the general management of common problems encountered in general practice, including asthma, diabetes, otitis media, hypertension, anxiety, and acute bronchitis. All studies examined physician behaviour and in three studies other health professionals such as nurses, nursing home attendants or health care workers were targeted. Positive effects on practice were observed in all studies. Only one study measured a patient outcome. Few studies examined the cost effectiveness of outreach. REVIEWER'S CONCLUSIONS: Educational outreach visits, particularly when combined with social marketing, appear to be a promising approach to modifying health professional behaviour, especially prescribing. Further research is needed to assess the effects of outreach visits for other aspects of practice and to identify key characteristics of outreach visits that are important to its success. The cost-effectiveness of outreach visits is not well evaluated.

Education, Medical, Continuing↗
PubMed1999

Clinical effectiveness of pneumococcal vaccine. Meta-analysis.

OBJECTIVE: To determine the clinical effectiveness of pneumococcal vaccine. DATA SOURCES: Computerized searches of MEDLINE, EMBASE, and SCISEARCH databases were performed, reference lists of retrieved articles were reviewed, and first authors of published studies were contacted. STUDY SELECTION: Studies of use of pneumococcal vaccines in adults were included if the study design was a randomized or quasi-randomized controlled trial and at least one of the following clinical outcomes was reported: vaccine-type systemic pneumococcal infection, systemic pneumococcal infection, vaccine-type pneumococcal pneumonia, pneumococcal pneumonia, non-vaccine-type pneumococcal pneumonia. SYNTHESIS: Study quality was assessed and descriptive information concerning the study populations, interventions, and outcome measurements was extracted for 13 trials involving more than 65,000 patients. Estimates of vaccine efficacy, based on a meta-analysis of randomized and quasi-randomized trials, were determined for clinical outcomes. CONCLUSIONS: Vaccination with pneumococcal polysaccharide vaccine can be expected to reduce the risk of systemic infection due to pneumococcal types included in the vaccine by 83% and systemic infection due to all pneumococci by 73%. We found no evidence that the vaccine was less efficacious for the elderly, institutionalized people, or those with chronic disease.

Adolescent↗
PubMed1998

The unpredictability paradox: review of empirical comparisons of randomised and non-randomised clinical trials.

OBJECTIVE: To summarise comparisons of randomised clinical trials and non-randomised clinical trials, trials with adequately concealed random allocation versus inadequately concealed random allocation, and high quality trials versus low quality trials where the effect of randomisation could not be separated from the effects of other methodological manoeuvres. DESIGN: Systematic review. SELECTION CRITERIA: Cohorts or meta-analyses of clinical trials that included an empirical assessment of the relation between randomisation and estimates of effect. DATA SOURCES: Cochrane Review Methodology Database, Medline, SciSearch, bibliographies, hand searching of journals, personal communication with methodologists, and the reference lists of relevant articles. MAIN OUTCOME MEASURES: Relation between randomisation and estimates of effect. RESULTS: Eleven studies that compared randomised controlled trials with non-randomised controlled trials (eight for evaluations of the same intervention and three across different interventions), two studies that compared trials with adequately concealed random allocation and inadequately concealed random allocation, and five studies that assessed the relation between quality scores and estimates of treatment effects, were identified. Failure to use random allocation and concealment of allocation were associated with relative increases in estimates of effects of 150% or more, relative decreases of up to 90%, inversion of the estimated effect and, in some cases, no difference. On average, failure to use randomisation or adequate concealment of allocation resulted in larger estimates of effect due to a poorer prognosis in non-randomly selected control groups compared with randomly selected control groups. CONCLUSIONS: Failure to use adequately concealed random allocation can distort the apparent effects of care in either direction, causing the effects to seem either larger or smaller than they really are. The size of these distortions can be as large as or larger than the size of the effects that are to be detected.

Clinical Trials as Topic↗