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PubMed1986

Regression analysis of aggregate accident data: some methodological considerations and practical experiences.

In empirical traffic safety studies regression analysis is perhaps the most widely used statistical technique. In the great majority of cases the regression model is applied in its standard form. If, however, highly aggregate accident data are analyzed, usually most of the assumptions of the standard model are violated. Referring to a practical study it is demonstrated how it may become difficult to decide whether or not a certain variable can be regarded as truly "explanatory." It appears that even in seemingly unproblematic situations contradictory results are obtained from only slightly different model specifications. It is recommended that the use of highly aggregate accident data be avoided whenever possible. Some hints are given concerning the use of appropriate extensions of the classical linear regression model in road accident studies.

Accidents, Traffic↗

PubMedDate not supplied

Assessing the clinical benefits of erythropoietic agents using area under the hemoglobin change curve.

INTRODUCTION: In assessing erythropoietic agents for chemotherapy-induced anemia, traditional single time-point end points (e.g., hematopoietic response [HR]) fail to reflect clinical benefits over the entire therapy course. Area under the hemoglobin change curve (Hb AUC) is introduced as an alternative measure, and its reliability, clinical significance, and superiority are assessed. METHODS: Using data from a phase IV open-label epoetin alfa (EPO) trial, we tested Hb AUC reliability by comparing its values derived from primary patient data with those derived from aggregated data. Clinical significance of the Hb AUC was investigated in three phase IV EPO trials by examining the linear relationship between Hb AUC quartiles and established clinical end points. The superiority of the Hb AUC over HR in its association with blood transfusion was tested through logistic regressions and area under the receiver operating characteristic (ROC) curve analysis. RESULTS: The Hb AUC values derived from patient and aggregated data were similar. Strong and statistically significant linear trends of decreasing transfusion requirements, increasing quality-of-life improvements, and decreasing time to HR were found across Hb AUC quartiles. The Hb AUC rendered the HR variable insignificant when both were present in the same model. Area under the ROC curve analysis supported the superior performance of the Hb AUC. CONCLUSIONS: We found that the Hb AUC is an objective, reliable, clinically meaningful, and comprehensive summary statistic that may be used to quantify clinical benefits for patients receiving erythropoietic agents. Further prospective validation of the Hb AUC metric is recommended.

Anemia↗

PubMed1998

Using scientific evidence to improve hospital library services: Southern Chapter/Medical Library Association journal usage study.

BACKGROUND: Journal usage studies, which are useful for budget management and for evaluating collection performance relative to library use, have generally described a single library or subject discipline. The Southern Chapter/Medical Library Association (SC/MLA) study has examined journal usage at the aggregate data level with the long-term goal of developing hospital library benchmarks for journal use. METHODS: Thirty-six SC/MLA hospital libraries, categorized for the study by size as small, medium, or large, reported current journal title use centrally for a one-year period following standardized data collection procedures. Institutional and aggregate data were analyzed for the average annual frequency of use, average costs per use and non-use, and average percent of non-used titles. Permutation F-type tests were used to measure difference among the three hospital groups. RESULTS: Averages were reported for each data set analysis. Statistical tests indicated no significant differences between the hospital groups, suggesting that benchmarks can be derived applying to all types of hospital libraries. The unanticipated lack of commonality among heavily used titles pointed to a need for uniquely tailored collections. CONCLUSION: Although the small sample size precluded definitive results, the study's findings constituted a baseline of data that can be compared against future studies.

Benchmarking↗

PubMed2002

Repair of groin hernia with synthetic mesh: meta-analysis of randomized controlled trials.

OBJECTIVE: To measure the effects of laparoscopic and open placement of synthetic mesh on recurrence and persisting pain following groin hernia repair. SUMMARY BACKGROUND DATA: Synthetic mesh techniques are claimed to reduce the risk of recurrence but there are concerns about costs and possible long-term complications, particularly pain. METHODS: Electronic databases were searched and experts consulted to identify randomized or quasi-randomized trials that compared mesh with non-mesh methods, or laparoscopic with open mesh placement. Individual patient data were sought for each trial. Aggregated data were used where individual patient data were not available. Meta-analyses of hernia recurrence and persisting pain were based on intention to treat. RESULTS: There were 62 relevant comparisons in 58 trials. These included 11,174 participants: individual patient data were available for 6,901 patients, supplementary aggregated data for 2,390 patients, and published data for 1883 patients. Recurrence and persisting pain were less after mesh repair (overall recurrences: 88 in 4,426 vs. 187 in 3,795; OR 0.43, 95% CI 0.34-0.55; P <.001) (overall persistent pain: 120 in 2,368 vs. 215 in 1,998; OR 0.36, 95% CI 0.29-0.46; P <.001), regardless of the non-mesh comparator. Whereas the reduction in recurrence was similar after laparoscopic and open mesh placement (OR 1.26, 95% CI 0.76-2.08; P =.36), persistent pain was less common after laparoscopic than open mesh placement (OR 0.64; 95% CI 0.52-0.78; P <.001). CONCLUSIONS: The use of synthetic mesh substantially reduces the risk of hernia recurrence irrespective of placement method. Mesh repair appears to reduce the chance of persisting pain rather than increase it.

Hernia, Inguinal↗

PubMed1998

Effectiveness of antibiotic prophylaxis in critically ill adult patients: systematic review of randomised controlled trials.

OBJECTIVE: To determine whether antibiotic prophylaxis reduces respiratory tract infections and overall mortality in unselected critically ill adult patients. DESIGN: Meta-analysis of randomised controlled trials from 1984 and 1996 that compared different forms of antibiotic prophylaxis used to reduce respiratory tract infections and mortality with aggregate data and, in a subset of trials, data from individual patients. SUBJECTS: Unselected critically ill adult patients; 5727 patients for aggregate data meta-analysis, 4343 for confirmatory meta-analysis with data from individual patients. MAIN OUTCOME MEASURES: Respiratory tract infections and total mortality. RESULTS: Two categories of eligible trials were defined: topical plus systemic antibiotics versus no treatment and topical preparation with or without a systemic antibiotic versus a systemic agent or placebo. Estimates from aggregate data meta-analysis of 16 trials (3361 patients) that tested combined treatment indicated a strong significant reduction in infection (odds ratio 0.35; 95% confidence interval 0.29 to 0.41) and total mortality (0.80; 0.69 to 0.93). With this treatment five and 23 patients would need to be treated to prevent one infection and one death, respectively. Similar analysis of 17 trials (2366 patients) that tested only topical antibiotics indicated a clear reduction in infection (0.56; 0.46 to 0.68) without a significant effect on total mortality (1.01; 0.84 to 1.22). Analysis of data from individual patients yielded similar results. No significant differences in treatment effect by major subgroups of patients emerged from the analyses. CONCLUSIONS: This meta-analysis of 15 years of clinical research suggests that antibiotic prophylaxis with a combination of topical and systemic drugs can reduce respiratory tract infections and overall mortality in critically ill patients. This effect is significant and worth while, and it should be considered when practice guidelines are defined.

Administration, Topical↗

PubMed2003

Laparoscopic techniques versus open techniques for inguinal hernia repair.

BACKGROUND: Inguinal hernia repair is the most frequently performed operation in general surgery. The standard method for inguinal hernia repair had changed little over a hundred years until the introduction of synthetic mesh. This mesh can be placed by either using an open approach or by using a minimal access laparoscopic technique. Although many studies have explored the relative merits and potential risks of laparoscopic surgery for the repair of inguinal hernia, most individual trials have been too small to show clear benefits of one type of surgical repair over another. OBJECTIVES: The objective of this review was to compare minimal access laparoscopic mesh techniques with open techniques. Comparisons of open mesh techniques versus open non-mesh techniques have been considered in a separate Cochrane review. SEARCH STRATEGY: We searched MEDLINE, EMBASE, and The Cochrane Central Controlled Trials Registry for relevant randomised controlled trials. The reference list of identified trials, journal supplements, relevant book chapters and conference proceedings were searched for further relevant trials. Through the EU Hernia Trialists Collaboration (EUHTC) communication took place with authors of identified randomised controlled trials to ask for information on any other recent and ongoing trials known to them. Specialists involved in research on the repair of inguinal hernia were contacted to ask for information about any further completed and ongoing trials. The world wide web was also searched. SELECTION CRITERIA: All published and unpublished randomised controlled trials and quasi-randomised controlled trials comparing laparoscopic groin hernia repair with open groin hernia repair were eligible for inclusion. Trials were included irrespective of the language in which they were reported. DATA COLLECTION AND ANALYSIS: Individual patient data were obtained, where possible, from the responsible trialist for all eligible studies. All reanalyses were cross-checked by the reviewers and verified by the trialists before inclusion. Where IPD were unavailable additional aggregate data were sought from trialists and published aggregate data checked and verified by the trialists. IPD were available for 25 trials, additional aggregated data for seven and published data only for nine. Where possible, time to event analysis for hernia recurrence and return to usual activities were performed on an intention to treat principle. The main analyses were based on all trials. Sensitivity analyses based on the data source and trial quality were also performed. Pre-defined subgroup analyses based on recurrent hernias, bilateral hernias and femoral hernias were also carried out. MAIN RESULTS: 41 published reports of eligible trials were included involving 7161 participants. Sample sizes ranged from 38 to 994, with follow-up from 6 weeks to 36 months. Duration of operation was longer in the laparoscopic groups (WMD 14.81 minutes, 95% CI 13.98 to 15.64; p<0001). Operative complications were uncommon for both methods but more frequent in the laparoscopic group for visceral (Overall 8/2315 versus 1/2599) and vascular (Overall 7/2498 versus 5/2758) injuries. Length of hospital stay did not differ between groups (WMD -0.04 days, 95% CI -0.08 to 0.00; p=0.05, but return to usual activity was earlier for laparoscopic groups (HR 0.56, 95%CI 0.51 to 0.61; p<0.0001 - equivalent to 7 days). The data available showed less persisting pain (Overall 290/2101 versus 459/2399; Peto OR 0.54, 95% CI 0.46 to 0.64; p<0.0001), and less persisting numbness (Overall 102/1419 versus 217/1624; Peto OR 0.38, 95% CI 0.4286 to 0.49; p<0.0001) in the laparoscopic groups. In total, 86 recurrences were reported amongst 3138 allocated laparoscopic repair and 109 amongst 3504 allocated to open repair (Peto OR 0.81, 95% CI 0.61 to 1.08; p = 0.16). The use of mesh during laparoscopic hernia repair is associated with a reduction in the risk of hernia recurrence, significantly so for the transabdominal preperitoneal repair (TAPP) versus open non-mesh repair (overall 26/1440 versus preperitoneal repair (TAPP) versus open non-mesh repair (overall 26/1440 versus 47/1119; Peto OR 0.45, 95% CI 0.28 to 0.72; p=0.0009). However, no difference was detected when comparing laparoscopic methods with open mesh methods of hernia repair. REVIEWER'S CONCLUSIONS: The use of mesh during laparoscopic hernia repair is associated with a relative reduction in the risk of hernia recurrence of around 30-50%. However, there is no apparent difference in recurrence between laparoscopic and open mesh methods of hernia repair. The data suggests less persisting pain and numbness following laparoscopic repair. Return to usual activities is faster. However, operation times are longer and there appears to be a higher risk of serious complication rate in respect of visceral (especially bladder) and vascular injuries.

Hernia, Inguinal↗

PubMed1992

Focus on psychometrics. Aggregating family data.

Instruments to collect data about families are often administered to all or some individuals within the family. Researchers may wish to use these individual scores to describe the family. The purpose of this article is to describe the special issues with aggregation of data when only a small number of family members are used as respondents. A refinement of the definition of aggregation for family researchers is proposed to assist researchers to focus on specific issues when data are to reflect subgroups within the family. A few examples of changes in findings are reported to illustrate the effects of different aggregation schemes when two members of the family are used as respondents.

Anxiety Disorders↗

PubMed1986

Conventional transmission electron microscopy of 1-1 haptoglobin isolated molecules and paracrystalline aggregates.

Data are presented relating conventional transmission electron microscope (CTEM) ultrastructural observations of the monomeric phenotypic variant (Hp 1-1) of the haptoglobin class of blood glycoproteins. Through comparison of these findings with homologous published data, obtained by means of scanning transmission electron microscopy (STEM), the validity of CTEM in molecule shape and fine structure determination is confirmed. An experimental procedure for Hp 1-1 crystallization is also reported.

Crystallization↗

PubMed2004

Use of antibiotics at hospitals in Stockholm: a benchmarking project using internet.

PURPOSE: To evaluate the internet way of feedback to prescribing physicians, providing data on antimicrobial use and to assess the applicability of the DU90% (i.e. Drug Utilisation 90%--the number of drugs accounting for 90% of the volume of usage in defined daily doses, (DDDs)) methodology in the hospital setting. METHODS: Antimicrobial drug use was evaluated in all major departments in seven hospitals in Stockholm in the year 2000. All data were presented anonymously on www.janusinfo.org. Aggregate data on antimicrobial drug use were expressed as the number of DDDs and costs per 100 bed-days. We focused on the number of drugs accounting for 90% of the volume (DDD), including the level of adherence to guidelines. The chief physicians assessed this feedback by a questionnaire. RESULTS: The number of DDDs/100 bed-days varied among different clinics and ranged from 39 to 57 (internal medicine) to 102 to 161 (infectious disease). The cost per 100 bed-days varied more than two-fold. The number of different antibiotics within the DU90% segment ranged from 9 to 13 (orthopaedic clinics) to 16 to 23 (infectious disease). According to the questionnaire, data were considered to be clearly presented and physicians would like to receive this kind of reports in the future, not only for antibiotics but also for other drugs. CONCLUSION: Presenting physicians with aggregate data on drug use via internet could provide a stimulus for prescribing improvement.

Anti-Bacterial Agents↗

PubMed2005

Investigating heterogeneity in an individual patient data meta-analysis of time to event outcomes.

Differences across studies in terms of design features and methodology, clinical procedures, and patient characteristics, are factors that can contribute to variability in the treatment effect between studies in a meta-analysis (statistical heterogeneity). Regression modelling can be used to examine relationships between treatment effect and covariates with the aim of explaining the variability in terms of clinical, methodological, or other factors. Such an investigation can be undertaken using aggregate data or individual patient data. An aggregate data approach can be problematic as sufficient data are rarely available and translating aggregate effects to individual patients can often be misleading. An individual patient data approach, although usually more resource demanding, allows a more thorough investigation of potential sources of heterogeneity and enables a fuller analysis of time to event outcomes in meta-analysis. Hierarchical Cox regression models are used to identify and explore the evidence for heterogeneity in meta-analysis and examine the relationship between covariates and censored failure time data in this context. Alternative formulations of the model are possible and illustrated using individual patient data from a meta-analysis of five randomized controlled trials which compare two drugs for the treatment of epilepsy. The models are further applied to simulated data examples in which the degree of heterogeneity and magnitude of treatment effect are varied. The behaviour of each model in each situation is explored and compared.

Anticonvulsants↗

PubMed1981

Reproducibility of observations on restorative and exodontic needs.

The reproducibility of observations on restorative and exodontic needs was studied by re-examination of a sample of secondary school students during a survey of dental status and need for treatment. Reproducibility was analysed by both a quantitative approach using aggregate data and a qualitative approach using tooth by tooth comparison. Reproducibility of all examiners as a collective group for the aggregate data was found to decrease as the frequency of observation of the category of treatment decreased. A lower level of reproducibility was found using the qualitative approach, even for the more frequently observed categories of treatment. Inter-examiner reproducibility was lower than intra-examiner reproducibility. The performance of individual examiners varied greatly. Based on the WHO (1977) definitions of satisfactory reproducibility, most examiners showed satisfactory intra-examiner reproducibility of the aggregate data, but a less satisfactory performance was found for the intra-examiner reproducibility using the qualitative approach, and for inter-examiner reproducibility using both approaches. Individual performance and severity of assessment of need for treatment overall were associated with the number of years since graduation of the examiners. The results indicated a need for strengthened procedures for selection and improved calibration of examiners. Calibration needed to be emphasized in the areas of occlusal lesions and need for one-surface restorations, and for the less frequently observed categories of treatment.

Adolescent↗

PubMed1993

Suicide and unemployment in Australia 1907-1990.

Ever since Durkheim postulated a relationship between economic change and suicide there has been evidence of a general association between aggregate data on unemployment and the frequency of suicide. Quantitatively, however, the association has been variable and it is clear that due to differing cultural, social and individual determinants of suicide, the relationship is complex. Methodological difficulties abound with interpretation of aggregate data. Australian records for most of the present century are suitable for examining secular trends in suicide and unemployment by age group and gender to gain an indication of the extent to which both parameters may be causally related. An aggregate/ecological study was designed to incorporate quantitative and qualitative strategies. Annual age-adjusted male and female suicide rates and annual unemployment rates were derived for the period 1907-1990. Female suicide rates were generally stable throughout the period, whereas those for males demonstrated sharp fluctuations with the peaks coinciding with times of high unemployment. The association between suicide and unemployment for 15-24 year old males was comparatively high for the recent period, 1966-1990. The increasingly youthful contribution to male suicide was demonstrated by a rise in the loss of life years during 1973-1984. Despite the inability of any investigation based on aggregate data to establish an unequivocable causal relationship, no evidence was detected to suggest that relatively high population levels of unemployment were not related to the occurrence of suicide.

Adolescent↗

PubMed2001

Using aggregate geographic data to proxy individual socioeconomic status: does size matter?

OBJECTIVES: This study assessed whether aggregate-level measures of socioeconomic status (SES) are less biased as proxies for individual-level measures if the unit of geographic aggregation is small in size and population. METHODS: National Health Interview Survey and census data were used to replicate analyses that identified the degree to which aggregate proxies of individual SES bias interpretations of the effects of SES on health. RESULTS: Ordinary least squares regressions on self-perceived health showed that the coefficients for income and education measured at the tract and block group levels were larger than those at the individual level but smaller than those estimated by Geronimus et al. at the zip code level. CONCLUSIONS: Researchers should be cautious about use of proxy measurement of individual SES even if proxies are calculated from small geographic units.

Data Collection↗

PubMed2005

Independent component analysis of fMRI group studies by self-organizing clustering.

Independent component analysis (ICA) is a valuable technique for the multivariate data-driven analysis of functional magnetic resonance imaging (fMRI) data sets. Applications of ICA have been developed mainly for single subject studies, although different solutions for group studies have been proposed. These approaches combine data sets from multiple subjects into a single aggregate data set before ICA estimation and, thus, require some additional assumptions about the separability across subjects of group independent components. Here, we exploit the application of similarity measures and a related visual tool to study the natural self-organizing clustering of many independent components from multiple individual data sets in the subject space. Our proposed framework flexibly enables multiple criteria for the generation of group independent components and their random-effects evaluation. We present real visual activation fMRI data from two experiments, with different spatiotemporal structures, and demonstrate the validity of this framework for a blind extraction and selection of meaningful activity and functional connectivity group patterns. Our approach is either alternative or complementary to the group ICA of aggregated data sets in that it exploits commonalities across multiple subject-specific patterns, while addressing as much as possible of the intersubject variability of the measured responses. This property is particularly of interest for a blind group and subgroup pattern extraction and selection.

Adult↗

PubMed2005

Ensuring the Quality of Aggregated General Practice Data: Lessons from the Primary Care Data Quality Programme (PCDQ).

BACKGROUND: There are large numbers of schemes that collect and aggregate data from primary care computer systems into large databases. These data are then used for market and academic research. How the data is aggregated, cleaned and processed is usually opaque. Making the method transparent allows researchers to compare methods, and users of the output to better understand the strengths and weaknesses of the data.Objectives To define the stages of the process of aggregating, processing and cleaning clinical data from multiple data sources. METHODS: Identify errors in design, collection, staging, integration and analysis. RESULTS: An eight step process defined: (1) Design (2) DATA: entry, (3) Extraction, (4) Migration, (5) Integration, (6) Cleaning, (7) Processing, and (8) Analysis. CONCLUSIONS: This eight step method provides a taxonomy to enable researchers to compare their methods of data process and aggregation.

Computer Systems↗

PubMed2002

Detailed postal feedback about prescribing to asthma patients combined with a guideline statement showed no impact: a randomised controlled trial.

OBJECTIVE: To evaluate the effects of postal feedback with clinically relevant data on general practitioners' prescribing compared with feedback with aggregate data on prescribing patterns of asthma drugs. METHODS: The study was a randomised, controlled trial. The general practitioners (GPs) in the County of Funen, Denmark (292 GPs representing 178 practices) were randomised to one of three groups receiving different forms of prescriber feedback. The first group received detailed and clinically relevant data on asthma drug prescribing patterns and a guideline statement. These data included tables with counts of asthma patients following classification of each individual's consumption of inhaled beta2-agonists and use of inhaled steroids. The second group received aggregate data on asthma drug prescribing patterns and a guideline statement, and the third group received feedback on an unrelated subject and served as control for the other groups. Each GP received prescriber feedback three times within a 6-month period. The last two letters with prescriber feedback had updated information with the purpose of showing changes in prescribing patterns. Effects were followed for a period of 1 year. The main outcome measures were change in fraction of asthmatics treated with inhaled steroids and incidence rate of treatment with inhaled steroids. RESULTS: The three groups had similar baseline characteristics. None of the two types of feedback on prescribing of asthma drugs had a statistically significant impact on GPs' prescribing patterns. CONCLUSION: Mailed prescriber feedback of detailed and clinically relevant data with a guideline statement, without revealing patient identities, has little or no impact on prescribing patterns.

Adolescent↗

PubMed1996

Focus groups: collecting aggregate-level data to understand community health phenomena.

Focus-group method is an apt strategy for studying community health phenomena at the aggregate level. Not only can its use facilitate the inclusion of segments of the population who have been underserved by previous research, but it can generate a depth of understanding about public health problems, community strengths, and potential interventions that have local meaning and utility. Advantages and potential uses of focus groups are explored, as well as purposes and processes of focus-group interviewing, strategies for analysis, methodological limitations, and implications for practice and policy. The author presents investigatory examples to illustrate how focus-group method expands on the possibilities of individual interviewing to explore community interpretations and understand the health needs and experiences of an aggregate.

Adult↗

PubMed2000

Clinical information systems.

Clinical information systems are the computer and information systems used by health care personnel to facilitate patient care. These systems have evolved from financial systems to true patient care systems with variable levels of functionality. Early systems provided laboratory and radiology results, and modern systems now provide copies of the radiology images and decision support for therapeutic orders. The rapidly changing technological infrastructure has created barriers to implementation of the electronic medical record, while coding schemes continue to be refined to enable data access and aggregate data analysis. Further refinement of clinical information systems is required before the potential value of these systems is realized in the clinical management of patients.

Child↗