Study Characteristics (study + characteristic)

Distribution by Scientific Domains


Selected Abstracts


Outcome of secondary root canal treatment: a systematic review of the literature

INTERNATIONAL ENDODONTIC JOURNAL, Issue 12 2008
Y.-L. Ng
Abstract Aims, (i) To investigate the effects of study characteristics on the reported success rates of secondary root canal treatment (2°RCT or root canal retreatment); and (ii) to investigate the effects of clinical factors on the success of 2°RCT. Methodology, Longitudinal human clinical studies investigating outcome of 2°RCT which were published upto the end of 2006 were identified electronically (MEDLINE and Cochrane database 1966,2006 Dec, week 4). Four journals (Dental Traumatology, International Endodontic Journal, Journal of Endodontics, Oral Surgery Oral Medicine Oral Pathology Endodontics Radiology), bibliographies of all relevant papers and review articles were hand-searched. Two reviewers (Y-LN, KG) independently assessed and selected the studies based on specified inclusion criteria and extracted the data onto a pre-designed proforma, independently. The criteria were: (i) Clinical studies on 2°RCT; (ii) Stratified analyses available for 2°RCT where 1°RCT data included; (iii) Sample size given and larger than 10; (iv) At least 6-month post-operative review; (v) Success based on clinical and/or radiographic criteria (strict = absence of apical radiolucency; loose = reduction in size of radiolucency); and (vi) Overall success rate given or could be calculated from the raw data. Three strands of evidence or analyses were used to triangulate a consensus view. The reported findings from individual studies, including those excluded for quantitative analysis, were utilized for the intuitive synthesis which constituted the first strand of evidence. Secondly, the pooled weighted success rates by each study characteristic and potential prognostic factor were estimated using the random effect model. Thirdly, the effects of study characteristics and prognostic factors (expressed as odds ratios) on success rates were estimated using fixed and random effects meta-analysis with DerSimonean and Laird's methods. Meta-regression models were used to explore potential sources of statistical heterogeneity. Study characteristics considered in the meta-regression analyses were: decade of publication, study-specific criteria for success (radiographic, combined radiographic & clinical), unit of outcome measure (tooth, root), duration after treatment when assessing success (,at least 4 years' or ,<4 years'), geographic location of the study (North American, Scandinavian, other countries), and qualification of the operator (undergraduate students, postgraduate students, general dental practitioners, specialist or mixed group). Results, Of the 40 papers identified, 17 studies published between 1961 and 2005 were included; none were published in 2006. The majority of studies were retrospective (n = 12) and only five prospective. The pooled weighted success rate of 2°RCT judged by complete healing was 76.7% (95% CI 73.6%, 89.6%) and by incomplete healing, 77.2% (95% CI 61.1%, 88.1%). The success rates by ,decade of publication' and ,geographic location of study' were not significantly different at the 5% level. Eighteen clinical factors had been investigated in various combinations in previous studies. The most frequently and thoroughly investigated were ,periapical status' (n = 13), ,size of lesion' (n = 7), and ,apical extent of RF' (n = 5) which were found to be significant prognostic factors. The effect of different aspects of primary treatment history and re-treatment procedures has been poorly tested. Conclusions, The pooled estimated success rate of secondary root canal treatment was 77%. The presence of pre-operative periapical lesion, apical extent of root filling and quality of coronal restoration proved significant prognostic factors with concurrence between all three strands of evidence whilst the effects of 1°RCT history and 2°RCT protocol have been poorly investigated. [source]


Outcome of secondary root canal treatment , Systematic review of the literature

INTERNATIONAL ENDODONTIC JOURNAL, Issue 5 2007
Y.-L. Ng
Aims, To assess the success rates of secondary root canal treatment (2oRCT) and identify factors influencing outcome. Methodology, Longitudinal clinical studies investigating outcome of 2oRCT were identified by electronic (medline) and hand searches. Inclusion criteria were data on: number of samples, those successful and definition of success. Two reviewers independently assessed the studies and extracted the data onto a proforma. The pooled weighted success rates by each potential prognostic factor were estimated using the binomial random effect model (MLwiN version 2.02) whilst their pooled effects (expressed as odds ratio) on success rates were estimated using fixed and random effects meta-analysis with DerSimonean and Laird's methods (Stata version 9.2). Meta-regression models were used to explore potential sources of statistical heterogeneity. Study characteristics considered in the meta-regression analyses were: decade of publication, study-specific criteria for success (radiographic, combined radiographic & clinical), unit of outcome measure (tooth and root), duration after treatment when assessing success (at least 4 years or shorter), geographic location of the study (North American, Scandinavian and other countries), and qualification of the operator (undergraduate students, postgraduate students, general dental practitioners, specialist or mixed group). Results, Of the 41 studies identified, 18 studies published between 1921 and 2005 were included. The majority of studies were retrospective (n = 13) and only five prospective. The pooled weighted success rate of 2oRCT judged by complete healing was 77.6% (95% CI 73.2%, 81.4%) and by incomplete healing, 77.4% (95% CI 64.1%, 86.7%). The success rates were similar by ,year of publication' and ,country of study'. Eighteen clinical factors were investigated in various combinations in previous studies. The most frequently investigated were ,periapical status' (n = 13), ,size of lesion' (n = 7), ,culture results prior to RF' (n = 5), and ,apical extent of root filling (RF)' (n = 4). The effect of different aspects of previous treatment and re-treatment technique has been poorly tested. Conclusions, The pooled weighted estimated success rate of 2oRCT was 77%, which was significantly (P , 0.001) influenced by the presence and size of pre-operative periapical lesion. The effects of existing canal content, procedural error and re-treatment technique were poorly investigated. [source]


Outcome of secondary root canal treatment: a systematic review of the literature

INTERNATIONAL ENDODONTIC JOURNAL, Issue 12 2008
Y.-L. Ng
Abstract Aims, (i) To investigate the effects of study characteristics on the reported success rates of secondary root canal treatment (2°RCT or root canal retreatment); and (ii) to investigate the effects of clinical factors on the success of 2°RCT. Methodology, Longitudinal human clinical studies investigating outcome of 2°RCT which were published upto the end of 2006 were identified electronically (MEDLINE and Cochrane database 1966,2006 Dec, week 4). Four journals (Dental Traumatology, International Endodontic Journal, Journal of Endodontics, Oral Surgery Oral Medicine Oral Pathology Endodontics Radiology), bibliographies of all relevant papers and review articles were hand-searched. Two reviewers (Y-LN, KG) independently assessed and selected the studies based on specified inclusion criteria and extracted the data onto a pre-designed proforma, independently. The criteria were: (i) Clinical studies on 2°RCT; (ii) Stratified analyses available for 2°RCT where 1°RCT data included; (iii) Sample size given and larger than 10; (iv) At least 6-month post-operative review; (v) Success based on clinical and/or radiographic criteria (strict = absence of apical radiolucency; loose = reduction in size of radiolucency); and (vi) Overall success rate given or could be calculated from the raw data. Three strands of evidence or analyses were used to triangulate a consensus view. The reported findings from individual studies, including those excluded for quantitative analysis, were utilized for the intuitive synthesis which constituted the first strand of evidence. Secondly, the pooled weighted success rates by each study characteristic and potential prognostic factor were estimated using the random effect model. Thirdly, the effects of study characteristics and prognostic factors (expressed as odds ratios) on success rates were estimated using fixed and random effects meta-analysis with DerSimonean and Laird's methods. Meta-regression models were used to explore potential sources of statistical heterogeneity. Study characteristics considered in the meta-regression analyses were: decade of publication, study-specific criteria for success (radiographic, combined radiographic & clinical), unit of outcome measure (tooth, root), duration after treatment when assessing success (,at least 4 years' or ,<4 years'), geographic location of the study (North American, Scandinavian, other countries), and qualification of the operator (undergraduate students, postgraduate students, general dental practitioners, specialist or mixed group). Results, Of the 40 papers identified, 17 studies published between 1961 and 2005 were included; none were published in 2006. The majority of studies were retrospective (n = 12) and only five prospective. The pooled weighted success rate of 2°RCT judged by complete healing was 76.7% (95% CI 73.6%, 89.6%) and by incomplete healing, 77.2% (95% CI 61.1%, 88.1%). The success rates by ,decade of publication' and ,geographic location of study' were not significantly different at the 5% level. Eighteen clinical factors had been investigated in various combinations in previous studies. The most frequently and thoroughly investigated were ,periapical status' (n = 13), ,size of lesion' (n = 7), and ,apical extent of RF' (n = 5) which were found to be significant prognostic factors. The effect of different aspects of primary treatment history and re-treatment procedures has been poorly tested. Conclusions, The pooled estimated success rate of secondary root canal treatment was 77%. The presence of pre-operative periapical lesion, apical extent of root filling and quality of coronal restoration proved significant prognostic factors with concurrence between all three strands of evidence whilst the effects of 1°RCT history and 2°RCT protocol have been poorly investigated. [source]


Prevalence of alcohol use disorders in schizophrenia , a systematic review and meta-analysis

ACTA PSYCHIATRICA SCANDINAVICA, Issue 2 2009
J. Koskinen
Objective:, Our aim was to present recent studies of alcohol use disorders (AUDs) in patients with schizophrenia, estimate overall prevalence and characteristics affecting the prevalence of AUDs. Method:, We conducted a search using three literature databases and a manual search on articles published in 1996,2008. Meta-regression was used to study how prevalence is affected by different study characteristics. Articles that reported diagnoses according to DSM or ICD diagnostic systems were included. Results:, Altogether 60 studies met our criteria. The median of current AUD prevalence was 9.4% (inter-quartile range, IQR 4.6,19.0, 18 studies) and median of lifetime AUD prevalence 20.6% (IQR 12.0,34.5, 47 studies). In studies using DSM-III-R median prevalence was higher than that in studies using DSM-IV, ICD-9 or ICD-10 (32/17/11/6%). Conclusion:, Approximately every fifth patient with schizophrenia had lifetime AUD diagnosis. When contrasted with the most recent review, there might be a descending trend in AUD prevalence in patients with schizophrenia. [source]


Self-injurious behavior and the efficacy of naltrexone treatment: A quantitative synthesis

DEVELOPMENTAL DISABILITIES RESEARCH REVIEW, Issue 3 2004
Frank J. Symons
Abstract People with mental retardation, autism, and related developmental disabilities who self-injure are treated with a wide array of behavioral techniques and psychotropic medications. Despite numerous reports documenting short-term and some long-term changes in self-injury associated with the opiate antagonist naltrexone hydrochloride, no quantitative review of its efficacy has been reported. We conducted a quantitative synthesis of the peer-reviewed published literature from 1983 to 2003 documenting the use of naltrexone for the treatment of self-injurious behavior (SIB). Individual-level results were analyzed given subject and study characteristics. A sample of 27 research articles involving 86 subjects with self-injury was reviewed. Eighty percent of subjects were reported to improve relative to baseline (i.e., SIB reduced) during naltrexone administration and 47% of subjects SIB was reduced by 50% or greater. In studies reporting dose levels in milligrams, males were more likely than females to respond. No significant relations were found between treatment outcomes and autism status or form of self-injury. Results are discussed with respect to future efficacy work related to study outcomes and the pharmacological treatment of self-injury. © 2004 Wiley-Liss, Inc. MRDD Research Reviews 2004;10:193,200. [source]


Effects of beverage alcohol price and tax levels on drinking: a meta-analysis of 1003 estimates from 112 studies

ADDICTION, Issue 2 2009
Alexander C. Wagenaar
ABSTRACT Aims We conducted a systematic review of studies examining relationships between measures of beverage alcohol tax or price levels and alcohol sales or self-reported drinking. A total of 112 studies of alcohol tax or price effects were found, containing1003 estimates of the tax/price,consumption relationship. Design Studies included analyses of alternative outcome measures, varying subgroups of the population, several statistical models, and using different units of analysis. Multiple estimates were coded from each study, along with numerous study characteristics. Using reported estimates, standard errors, t -ratios, sample sizes and other statistics, we calculated the partial correlation for the relationship between alcohol price or tax and sales or drinking measures for each major model or subgroup reported within each study. Random-effects models were used to combine studies for inverse variance weighted overall estimates of the magnitude and significance of the relationship between alcohol tax/price and drinking. Findings Simple means of reported elasticities are ,0.46 for beer, ,0.69 for wine and ,0.80 for spirits. Meta-analytical results document the highly significant relationships (P < 0.001) between alcohol tax or price measures and indices of sales or consumption of alcohol (aggregate-level r = ,0.17 for beer, ,0.30 for wine, ,0.29 for spirits and ,0.44 for total alcohol). Price/tax also affects heavy drinking significantly (mean reported elasticity = ,0.28, individual-level r = ,0.01, P < 0.01), but the magnitude of effect is smaller than effects on overall drinking. Conclusions A large literature establishes that beverage alcohol prices and taxes are related inversely to drinking. Effects are large compared to other prevention policies and programs. Public policies that raise prices of alcohol are an effective means to reduce drinking. [source]


Estimation of the burden of active and life-time epilepsy: A meta-analytic approach

EPILEPSIA, Issue 5 2010
Anthony K. Ngugi
Summary Purpose:, To estimate the burden of lifetime epilepsy (LTE) and active epilepsy (AE) and examine the influence of study characteristics on prevalence estimates. Methods:, We searched online databases and identified articles using prespecified criteria. Random-effects meta-analyses were used to estimate the median prevalence in developed countries and in urban and rural settings in developing countries. The impact of study characteristics on prevalence estimates was determined using meta-regression models. Results:, The median LTE prevalence for developed countries was 5.8 per 1,000 (5th,95th percentile range 2.7,12.4) compared to 15.4 per 1,000 (4.8,49.6) for rural and 10.3 (2.8,37.7) for urban studies in developing countries. The median prevalence of AE was 4.9 per 1,000 (2.3,10.3) for developed countries and 12.7 per 1,000 (3.5,45.5) and 5.9 (3.4,10.2) in rural and urban studies in developing countries. The estimates of burden for LTE and AE in developed countries were 6.8 million (5th,95th percentile range 3.2,14.7) and 5.7 million (2.7,12.2), respectively. In developing countries these were 45 (14,145) million LTE and 17 (10,133) million AE in rural areas and 17 (5,61) million LTE and 10 (5,17) million AE in urban areas. Studies involving all ages or only adults showed higher estimates than pediatric studies. Higher prevalence estimates were also associated with rural location and small study size. Conclusions:, This study estimates the global burden of epilepsy and the proportions with AE, which may benefit from treatment. There are systematic differences in reported prevalence estimates, which are only partially explained by study characteristics. [source]


Outcome of secondary root canal treatment: a systematic review of the literature

INTERNATIONAL ENDODONTIC JOURNAL, Issue 12 2008
Y.-L. Ng
Abstract Aims, (i) To investigate the effects of study characteristics on the reported success rates of secondary root canal treatment (2°RCT or root canal retreatment); and (ii) to investigate the effects of clinical factors on the success of 2°RCT. Methodology, Longitudinal human clinical studies investigating outcome of 2°RCT which were published upto the end of 2006 were identified electronically (MEDLINE and Cochrane database 1966,2006 Dec, week 4). Four journals (Dental Traumatology, International Endodontic Journal, Journal of Endodontics, Oral Surgery Oral Medicine Oral Pathology Endodontics Radiology), bibliographies of all relevant papers and review articles were hand-searched. Two reviewers (Y-LN, KG) independently assessed and selected the studies based on specified inclusion criteria and extracted the data onto a pre-designed proforma, independently. The criteria were: (i) Clinical studies on 2°RCT; (ii) Stratified analyses available for 2°RCT where 1°RCT data included; (iii) Sample size given and larger than 10; (iv) At least 6-month post-operative review; (v) Success based on clinical and/or radiographic criteria (strict = absence of apical radiolucency; loose = reduction in size of radiolucency); and (vi) Overall success rate given or could be calculated from the raw data. Three strands of evidence or analyses were used to triangulate a consensus view. The reported findings from individual studies, including those excluded for quantitative analysis, were utilized for the intuitive synthesis which constituted the first strand of evidence. Secondly, the pooled weighted success rates by each study characteristic and potential prognostic factor were estimated using the random effect model. Thirdly, the effects of study characteristics and prognostic factors (expressed as odds ratios) on success rates were estimated using fixed and random effects meta-analysis with DerSimonean and Laird's methods. Meta-regression models were used to explore potential sources of statistical heterogeneity. Study characteristics considered in the meta-regression analyses were: decade of publication, study-specific criteria for success (radiographic, combined radiographic & clinical), unit of outcome measure (tooth, root), duration after treatment when assessing success (,at least 4 years' or ,<4 years'), geographic location of the study (North American, Scandinavian, other countries), and qualification of the operator (undergraduate students, postgraduate students, general dental practitioners, specialist or mixed group). Results, Of the 40 papers identified, 17 studies published between 1961 and 2005 were included; none were published in 2006. The majority of studies were retrospective (n = 12) and only five prospective. The pooled weighted success rate of 2°RCT judged by complete healing was 76.7% (95% CI 73.6%, 89.6%) and by incomplete healing, 77.2% (95% CI 61.1%, 88.1%). The success rates by ,decade of publication' and ,geographic location of study' were not significantly different at the 5% level. Eighteen clinical factors had been investigated in various combinations in previous studies. The most frequently and thoroughly investigated were ,periapical status' (n = 13), ,size of lesion' (n = 7), and ,apical extent of RF' (n = 5) which were found to be significant prognostic factors. The effect of different aspects of primary treatment history and re-treatment procedures has been poorly tested. Conclusions, The pooled estimated success rate of secondary root canal treatment was 77%. The presence of pre-operative periapical lesion, apical extent of root filling and quality of coronal restoration proved significant prognostic factors with concurrence between all three strands of evidence whilst the effects of 1°RCT history and 2°RCT protocol have been poorly investigated. [source]


Outcome of primary root canal treatment: systematic review of the literature , Part 2.

INTERNATIONAL ENDODONTIC JOURNAL, Issue 1 2008
Influence of clinical factors
Abstract Aims, (i) To carry out meta-analyses to quantify the influence of the clinical factors on the efficacy of primary root canal treatment and (ii) to identify the best treatment protocol based on the current evidence. Methodology, The evidence for the effect of each clinical factor on the success rate (SR) of primary root canal treatment was gathered in three different ways: (i) intuitive synthesis of reported findings from individual studies; (ii) weighted pooled SR by each factor under investigation was estimated using random-effect meta-analysis; (iii) weighted effect of the factor under investigation on SR were estimated and expressed as odds ratio for the dichotomous outcomes (success or failure) using fixed- and random-effects meta-analysis. Statistical heterogeneity amongst the studies was assessed by Cochran's (Q) test. Potential sources of statistical heterogeneity were investigated by exploring clinical heterogeneity using meta-regression models which included study characteristics in the regression models. Results, Out of the clinical factors investigated, pre-operative pulpal and periapical status were most frequently investigated, whilst the intra-operative factors were poorly studied in the 63 studies. Four factors were found to have a significant effect on the primary root canal treatment outcome, although the data heterogeneity was substantial, some of which could be explained by some of the study characteristics. Conclusions, Four conditions (pre-operative absence of periapical radiolucency, root filling with no voids, root filling extending to 2 mm within the radiographic apex and satisfactory coronal restoration) were found to improve the outcome of primary root canal treatment significantly. Root canal treatment should therefore aim at achieving and maintaining access to apical anatomy during chemo-mechanical debridement, obturating the canal with densely compacted material to the apical terminus without extrusion into the apical tissues and preventing re-infection with a good quality coronal restoration. [source]


International Differences in Nursing Research, 2005,2006

JOURNAL OF NURSING SCHOLARSHIP, Issue 1 2009
Denise F. Polit PhD
Abstract Purpose: To compare the characteristics of nursing research being done in different countries, using data from studies published in nonspecialty, English-language nursing journals. Design: Data for this cross-sectional analysis were retrieved from a consecutive sample of 1,072 studies published in eight leading English-language research journals in 2005 and 2006. Methods: For each study, data were extracted on the characteristics of the study participants and authors, study focus-specialty area, funding, and methodologic attributes. Studies from 15 countries or regional groupings were compared. Findings: International differences in authors, participants, and study characteristics were typically large and statistically significant. Studies that were focused on nurses were especially prevalent in Europe, Australia, and Canada, whereas patient-centered studies were most common in Asian countries and the US. Qualitative studies were predominant in Norway, Sweden, and the UK. Asian nurse researchers, by contrast, undertook mostly quantitative studies, and were especially likely to conduct intervention research. Significant country differences existed in the omission of demographic (age and sex) information about participants, with omissions most prevalent in the UK and Ireland and least prevalent in Asian countries. Research funding was reported for 62% of all studies, ranging from 13% in Turkey to over 75% in Canada and the US. Conclusions: Although this study had several limitations, especially with regard to potential biases in the sample of studies from non-English-speaking countries, this analysis of over 1,000 nursing studies indicates many important inter-country differences in the focus, methods, and authorship patterns of nursing research published in leading journals. Clinical Relevance: Because research "informs" practice, international differences that exist in the focus and methods of nursing research have implications for nursing practice in the respective countries. [source]


Effective Methods to Improve Recruitment and Retention in School-Based Substance Use Prevention Studies

JOURNAL OF SCHOOL HEALTH, Issue 9 2009
Jean-Marie Bruzzese PhD
ABSTRACT BACKGROUND: Poor recruitment and high attrition may invalidate results of research studies. This paper describes successful recruitment and retention strategies in a school-based substance use prevention trial and explores factors associated with intervention attendance and retention. METHODS: A total of 384 parent-child dyads from 15 schools in the New York Metropolitan area participated in a control trial, testing the efficacy of parent-training to prevent youth substance use. Assessments were completed immediately post-intervention and 6-, 12-, and 24-month postintervention. Logistic regression analyses were used to determine which familial and study characteristics predicted attendance in the intervention and retention by parents and youth. RESULTS: 84% of intervention parents attended 4 of the 5 workshops; 83% of control parents attended their single workshop. Intervention attendance was predicted by parent job status, but this was not significant after controlling for other family factors. Retention rates ranged from 87% to 91% over the 2 years. No family characteristics predicted retention, but time since baseline and attendance at treatment workshops and the control workshop did. For children, age at baseline and ethnicity predicted retention, but this did not remain significant in the adjusted model. CONCLUSION: Intervention attendance was high and retention rates far exceeded the minimum standard of 70% retention in behavioral studies. Recruitment and retention strategies were effective for different family constellations. Efforts to maximize participation in both treatment and control interventions are critical to retention in longitudinal trials. [source]


Diagnostic accuracy of D-dimer test for exclusion of venous thromboembolism: a systematic review

JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 2 2007
M. DI NISIO
Summary.,Background: The reported diagnostic accuracy of the D-dimer test for exclusion of deep vein thrombosis (DVT) and pulmonary embolism (PE) varies. It is unknown to what extent this is due to differences in study design or patient groups, or to genuine differences between D-dimer assays. Methods: Studies evaluating the diagnostic accuracy of the D-dimer test in the diagnosis of venous thromboembolism were systematically searched for in the MEDLINE and EMBASE databases up to March 2005. Reference lists of all included studies and of reviews related to the topic of the present meta-analysis were manually searched for other additional potentially eligible studies. Two reviewers independently extracted study characteristics using standardized forms. Results: In total, 217 D-dimer test evaluations for DVT and 111 for PE were analyzed. Several study design characteristics were associated with systematic differences in diagnostic accuracy. After adjustment for these features, the sensitivities of the D-dimer enzyme-linked immunofluorescence assay (ELFA) (DVT 96%; PE 97%), microplate enzyme-linked immunosorbent assay (ELISA) (DVT 94%; PE 95%), and latex quantitative assay (DVT 93%; PE 95%) were superior to those of the whole-blood D-dimer assay (DVT 83%; PE 87%), latex semiquantitative assay (DVT 85%; PE 88%) and latex qualitative assay (DVT 69%; PE 75%). The latex qualitative and whole-blood D-dimer assays had the highest specificities (DVT 99%, 71%; PE 99%, 69%). Conclusions: Compared to other D-dimer assays, the ELFA, microplate ELISA and latex quantitative assays have higher sensitivity but lower specificity, resulting in a more confident exclusion of the disease at the expense of more additional imaging testing. These conclusions are based on the most up-to-date and extensive systematic review of the topic area, including 184 articles, with 328 D-dimer test evaluations. [source]


Influences of study design and location on the relationship between particulate matter air pollution and birthweight

PAEDIATRIC & PERINATAL EPIDEMIOLOGY, Issue 3 2008
Jennifer D. Parker
Summary A large number of studies have identified a relationship between particulate matter air pollution and birthweight. Although reported associations are small and varied, they have been identified in studies from places around the world. Exposure assignment, covariates and study inclusion criteria vary among studies. To examine the effect of these and other study characteristics on associations between particulate matter and birthweight, US birth records for singletons delivered at 40 weeks gestation in 2001,03 during the months of March, June, September and December were linked to quarterly estimates of pollution exposure, both particulate matter exposure and exposure to multiple pollutants, by county of residence and month of birth. Annual, 9-month and trimester-specific exposures were assigned. Among births linked to particulate matter exposure there was a small association between coarse particle exposure and birthweight (beta ,13 g per 10 µg/m3 increase [95% CI ,18.3 g, ,7.6 g]) after controlling for maternal factors; this association was attenuated slightly and remained statistically significant after further adjustment for contextual factors, year of birth, region, or urban,rural status. The associations were slightly weaker among births linked to multiple pollutant exposure than among births linked to just particulate matter exposure. The association varied markedly by region, ranging from a decrement of 43 g per 10 µg/m3[95% CI ,58.6 g, ,27.6 g] in the north-west to a null association in the south-west. Trimester findings were smaller, yet remained significant and varied regionally. The association between fine particle exposure and birthweight varied considerably, with an overall small positive association that became null after control for region. This study found that wide regional differences in association may contribute to the varied published findings. The association between coarse particle exposure and birthweight appeared robust, if small; fine particles had no overall association with birthweight. [source]


Replication of the Scandinavian Simvastatin Survival Study using a primary care medical record database prompted exploration of a new method to address unmeasured confounding

PHARMACOEPIDEMIOLOGY AND DRUG SAFETY, Issue 7 2008
Mark G. Weiner M.D.
Abstract Purpose To examine whether identifiable study characteristics and/or analytic methods used determine observational study validity, as assessed by replicating randomized controlled trials using observational data. Methods A cohort from the United Kingdom General Practice Research Database (GPRD) was used to replicate the Scandinavian Simvastatin Survival Study RCT, which investigated statin treatment of hypercholesterolemic subjects with coronary heart disease. All aspects of the RCT except randomization were replicated to the extent possible in the GPRD study, which included 2,871 Unexposed and 1,280 statin-treated Exposed subjects. Results Overall mortality [adjusted hazard ratio 0.71 (0.53,0.96)] and myocardial infarction [adjusted HR 0.79 (0.61,1.02)] decreased in the GPRD study similar to the RCT. Coronary revascularization increased two-fold in the GPRD study, whereas it decreased significantly in the RCT [0.63 (0.54,0.74)]. This latter disparity prompted use of a new methodology to adjust for unmeasured confounding, which yielded an adjusted HR [1.0 (0.75,1.33)] more comparable to the RCT. Conclusions This study provides additional evidence that a replicated GPRD observational study can yield results reasonably similar to a RCT. More important, it provides preliminary evidence suggesting that a new analytic methodology may adjust for unmeasured confounding, the major limitation to research using observational data. Copyright © 2008 John Wiley & Sons, Ltd. [source]


The income elasticity of meat: a meta-analysis

AUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 4 2010
Craig A. Gallet
The demand for meat has been estimated by many studies utilizing various data and estimation methods. In this study, we perform a meta-analysis of the income elasticity of meat that involves regressing 3357 estimated income elasticities, collected from 393 studies, on variables that control for study characteristics. Across several meta-regression specifications, we find significant differences in income elasticities tied to the type of meat being studied, as well as a few functional forms, data aggregations, publication characteristics, and locations of demand. However, many study characteristics do not significantly influence reported income elasticities. Less concern should be given to such characteristics when choosing an income elasticity from the literature. [source]


The demand for alcohol: a meta-analysis of elasticities,

AUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 2 2007
Craig A. Gallet
Numerous studies have estimated elasticities of alcohol demand using different procedures. Because of widespread differences in demand estimates, however, it is difficult to synthesise the literature into coherent meaning. This study improves our understanding of alcohol demand by reporting results from a meta-analysis of 132 studies. Specifically, regressing estimated price, income and advertising elasticities of alcohol on variables accounting for study characteristics, we find alcohol elasticities to be particularly sensitive to demand specification, data issues and various estimation methods. Furthermore, compared to other alcoholic beverages, beer elasticities tend to be more inelastic. [source]


The role of microarthropods in terrestrial decomposition: a meta-analysis of 40 years of litterbag studies

BIOLOGICAL REVIEWS, Issue 3 2009
Christian Kampichler
ABSTRACT Litterbags have been utilized in soil ecology for about 50 years. They are useful because they confine organic material and thus enable the study of decomposition dynamics (mass loss and/or nutrient loss through time, colonization by soil biota) in situ, i.e. under field conditions. Researchers can easily restrict or permit access to certain size classes of soil fauna to determine their contribution to litter mass loss by choosing adequate mesh size or applying specific biocides. In particular, the mesofauna has received much attention since it comprises two very abundant and diverse microarthropod groups, the Collembola (springtails) and Acari (mites). We comprehensively searched the literature from the mid-1960s to the end of 2005 for reports on litterbag experiments investigating the role of microarthropods in terrestrial decomposition. Thirty papers reporting 101 experiments satisfied our selection criteria and were included in the database. Our meta-analysis revealed that microarthropods have a moderate but significant effect on mass loss. We discuss in detail the interactions of the microarthropod effect with study characteristics such as experimental design (e.g. number of bags, duration of experiment), type of exposed organic matter, climatic zone and land use of the study site. No publication bias was detected; however, we noticed a significant decrease in the microarthropod effect with publication year, indicating that, in the first decades of litterbag use, soil zoologists may have studied "promising" sites with a higher a priori probability of positive microarthropod effects on litter mass loss. A general weakness is that the treatments differ not only with respect to the presence or absence of microarthropods, but also with regard to mesh size (small to exclude microarthropods, wide to permit their access) or presence (to exclude microarthropods) and absence (to permit their access) of an insecticide. Consequently, the difference between the decomposition rates in the treatments is not a pure microarthropod effect but will be influenced by the additive effects of mesh size and insecticide. The relative contribution of the "true" microarthropod effect remains unknown without additional treatments controlling for the differential mesh size/insecticide effect. A meta-analysis including only those studies using different mesh size and for which the data were corrected by subtracting an estimated mesh size effect based on data from the literature yielded a significantly negative microarthropod effect on litter decomposition. These results cast doubt on the widely accepted hypothesis that microarthropods generally exert a positive effect on litter mass loss. We conclude that after 40 years of litterbag studies our knowledge on the role of microarthropods in litter mass loss remains limited and that the inclusion of a third treatment in future studies is a promising way to retain litterbags as a meaningful tool of soil biological studies. [source]