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Biomedical subjects

James Carpenter

Publications and source records attributed to James Carpenter.

10 recordsLinked to original sources
PubMed2006

The relationship between quality of research and citation frequency.

BACKGROUND: Citation counts are often regarded as a measure of the utilization and contribution of published articles. The objective of this study is to assess whether statistical reporting and statistical errors in the analysis of the primary outcome are associated with the number of citations received. METHODS: We evaluated all original research articles published in 1996 in four psychiatric journals. The statistical and reporting quality of each paper was assessed and the number of citations received up to 2005 was obtained from the Web of Science database. We then examined whether the number of citations was associated with the quality of the statistical analysis and reporting. RESULTS: A total of 448 research papers were included in the citation analysis. Unclear or inadequate reporting of the research question and primary outcome were not statistically significantly associated with the citation counts. After adjusting for journal, extended description of statistical procedures had a positive effect on the number of citations received. Inappropriate statistical analysis did not affect the number of citations received. Adequate reporting of the primary research question, statistical methods and primary findings were all associated with the journal visibility and prestige. CONCLUSION: In this cohort of published research, measures of reporting quality and appropriate statistical analysis were not associated with the number of citations. The journal in which a study is published appears to be as important as the statistical reporting quality in ensuring dissemination of published medical science.

Bibliometrics↗
PubMed2006

A brief measure of perceived understanding of informed consent in a clinical trial was validated.

BACKGROUND AND OBJECTIVE: To develop and evaluate an Informed Consent Questionnaire (ICQ) for measuring self-reported perceived understanding of informed consent in a randomized clinical trial. METHODS: The study was embedded in a Department of Veterans Affairs randomized clinical trial of Gulf War veterans' illnesses (CSP#470). The trial was initiated in May 1999 at 20 hospitals and concluded in September 2001; 1,092 participants were enrolled and followed for 12 months. The reliability and validity sample included 1,086 participants evaluated at baseline, 906 at 3 months, 929 at 6 months, and 910 at 12 months. The psychometric evaluations included tests of acceptability (based on missing data, endorsement frequencies, and floor/ceiling effects), item reduction, internal consistency, and construct validity (based on Cronbach's alpha coefficients, item-total correlations, and principal components analysis). RESULTS: The ICQ had >5% missing information on some questions at baseline, indicating poor acceptability prior to the initiation of the trial; however, the scale had good acceptability at each of the follow-up visits. Psychometric evaluation following standard item reduction techniques confirmed the reliability and validity of a four-item subscale of the ICQ (ICQ-4). CONCLUSIONS: The ICQ-4 is a simple and psychometrically sound self-report measure of perceived understanding of informed consent.

Adult↗
PubMed2006

Consumer involvement in consent document development: a multicenter cluster randomized trial to assess study participants' understanding.

BACKGROUND: Despite widespread agreement on the importance of informed consent in clinical research, uncertainty remains about the adequacy of current consent procedures and documentation. METHODS: The objective of the study was to compare an informed consent document developed by a consumer group of potential study participants to one developed by the study investigators. The study was a cluster randomized, controlled study embedded in a 'parent' randomized controlled trial of 1092 participants with Gulf War veterans' illnesses recruited in 1999-2000 at 20 US medical centers. Centers were randomized to the investigator-developed or participant-developed consent document. The primary outcome measure was an Informed Consent Questionnaire-4 (ICQ-4), a validated four-item scale measuring self-reported participant understanding scored from 0 to 1. Secondary outcomes included the Client Satisfaction Questionnaire-8 and measures of study refusal and adherence to the parent trial protocol. RESULTS: There were no significant differences between consent documents on the ICQ-4 score overall or at any of the time points. Mean (95% CI) treatment differences ranged from +0.020 (-0.015, 0.055) (better understanding) at entry to -0.021 (-0.054, 0.012) (worse understanding) at three-months for the participant versus the investigator document group. There were also no significant differences in satisfaction, adherence to the protocol, or in the proportion of patients who refused to participate in the trial. LIMITATIONS: The consumer group may not have been representative of the study participants and they did not suggest dramatic changes to the consent document. The outcome assessment questionnaire was not validated prior to the trial's initiation. CONCLUSIONS: Consumer modification of the consent document did not lead to either benefit or harm in understanding, satisfaction, or study refusal and adherence rates. This study did demonstrate, however, that embedding consent studies in a clinical trial is feasible and can address important questions about informed consent without disrupting the primary study.

Adult↗
PubMed2004

Comparison of imputation and modelling methods in the analysis of a physical activity trial with missing outcomes.

BACKGROUND: Longitudinal studies almost always have some individuals with missing outcomes. Inappropriate handling of the missing data in the analysis can result in misleading conclusions. Here we review a wide range of methods to handle missing outcomes in single and repeated measures data and discuss which methods are most appropriate. METHODS: Using data from a randomized controlled trial to compare two interventions for increasing physical activity, we compare complete-case analysis; ad hoc imputation techniques such as last observation carried forward and worst-case; model-based imputation; longitudinal models with random effects; and recently proposed joint models for repeated measures data and non-ignorable dropout. RESULTS: Estimated intervention effects from ad hoc imputation methods vary widely. Standard multiple imputation and longitudinal modelling agree closely, as they should. Modifying the modelling method to allow for non-ignorable dropout had little effect on estimated intervention effects, but imputing using a common imputation model in both groups gave more conservative results. CONCLUSIONS: Results from ad hoc imputation methods should be avoided in favour of methods with more plausible assumptions although they may be computationally more complex. Although standard multiple imputation methods and longitudinal modelling methods are equivalent for estimating the treatment effect, the two approaches suggest different ways of relaxing the assumptions, and the choice between them depends on contextual knowledge.

Bias↗
PubMed2004

Injury patterns in big ten conference football.

BACKGROUND: In 1998, the National Collegiate Athletic Association legislated a decrease in the number of scrimmages and full-contact practices allowed during the spring season. HYPOTHESIS: A significantly increased risk of injury faced by the same player during the spring versus fall practice sessions does exist, but the National Collegiate Athletic Association regulations will not have the intended effect of reducing injury rates to equal or below those of the fall practice sessions. STUDY DESIGN: Retrospectively analyzed, descriptive study of prospectively collected injury surveillance data followed by a prospective, controlled, repeated-measures study after the rule change. METHODS: Phase 1: the Big Ten Conference Sports Injury Surveillance System database was reviewed from spring 1992 through fall 1997 for all reportable injuries. Phase 2: a prospective investigation was instituted from spring 1998 through fall 2000. This protocol was modified to also document updated individual player position descriptions and string as well as exposures for the old fall and spring practice categories (scrimmages, full contact, and limited contact) and the new spring practice designations (full pads with and without tackling, helmets only, spring game, and other scrimmages). RESULTS: Phase 1: There were 3950 fall injuries and 1007 spring injuries, with 469 of the 1007 attributable to the "spring risk factor." There was a statistically significant increase in injury rate in the spring (19.8) versus fall (10.6). Scrimmages (incidence density ratio = 2.4) and limited-contact practices (incidence density ratio = 2.5) showed more than twice the fall injury rate. Phase 2: There were 1502 fall injuries and 648 spring injuries, with 192 attributable to the spring risk factor. There was a 3-fold increase in injury rate in the spring (incidence density ratio = 3.2). Although the noncontact, helmets-only practices produced the lowest injury rates, the nonspring game scrimmages and the limited-contact practices defined as "practice with pads but without tackling" displayed the highest injury rates. In both spring and fall, nonplayers exhibited the highest injury rates for all string groups. CONCLUSIONS: There was and still is a statistically significant increase in spring practice injury risk. The 1998 rule change resulted in an even greater increase in spring practice injury risk. If the goal is to minimize the number of spring practice injuries, it will be best accomplished by limiting the number of scrimmages and limited-contact sessions.

Adult↗
PubMed2004

Effects of training on quality of peer review: randomised controlled trial.

OBJECTIVE: To determine the effects of training on the quality of peer review. DESIGN: Single blind randomised controlled trial with two intervention groups receiving different types of training plus a control group. SETTING AND PARTICIPANTS: Reviewers at a general medical journal. Interventions Attendance at a training workshop or reception of a self taught training package focusing on what editors want from reviewers and how to critically appraise randomised controlled trials. MAIN OUTCOME MEASURES: Quality of reviews of three manuscripts sent to reviewers at four to six monthly intervals, evaluated using the validated review quality instrument; number of deliberate major errors identified; time taken to review the manuscripts; proportion recommending rejection of the manuscripts. RESULTS: Reviewers in the self taught group scored higher in review quality after training than did the control group (score 2.85 v 2.56; difference 0.29, 95% confidence interval 0.14 to 0.44; P = 0.001), but the difference was not of editorial significance and was not maintained in the long term. Both intervention groups identified significantly more major errors after training than did the control group (3.14 and 2.96 v 2.13; P < 0.001), and this remained significant after the reviewers' performance at baseline assessment was taken into account. The evidence for benefit of training was no longer apparent on further testing six months after the interventions. Training had no impact on the time taken to review the papers but was associated with an increased likelihood of recommending rejection (92% and 84% v 76%; P = 0.002). CONCLUSIONS: Short training packages have only a slight impact on the quality of peer review. The value of longer interventions needs to be assessed.

Education, Professional↗
PubMed2003

The use of regression models for medians when observed outcomes may be modified by interventions.

Some outcomes used in epidemiological studies and clinical trials are prone to modification by interventions, for example, individuals with high blood pressure are likely to receive antihypertensive medication. Often the scientific interest is in the relationship of covariates (exposures or randomized treatment) to the outcomes that would have been observed in the absence of intervention. We compare three approaches to the analysis of such data: ignoring the intervention; excluding individuals who receive the intervention, and assuming that individuals who receive the intervention have underlying outcomes above the median. The latter approach requires comparison of median outcomes between groups. In many situations it is plausible that neither the probability of intervention nor the effect of intervention depend on the covariates. In this case we show that analysis of medians is unbiased in general, that the other approaches are biased towards the null but that ignoring the intervention typically has the greatest power for detecting an effect. In other situations, ignoring the intervention and excluding individuals who receive the intervention may be biased towards or away from the null, and we recommend analysis of medians. We illustrate practical analysis of medians in a study of the association between adult blood pressure and birth weight. Adjustment for confounders is performed by median regression. We show that the significance levels are comparable to those derived from logistic regression. We also discuss the effect of grouping of blood pressure and the need for bootstrap standard errors.

Antihypertensive Agents↗
PubMed2003

Adjusting treatment comparisons to account for non-randomized interventions: an example from an angina trial.

In a clinical trial where some subjects receive one or more non-randomized interventions during follow-up, primary interest is in the effect of the overall treatment strategies as implemented, but it may also be of interest to adjust treatment comparisons for non-randomized interventions. We consider non-randomized interventions, especially surgical procedures, which only occur when the outcome would otherwise have been poor. Focusing on an outcome measured repeatedly over time, we describe the variety of questions that may be addressed by an adjusted analysis. The adjusted analyses involve new outcome variables defined in terms of the observed outcomes and the history of non-randomized intervention. We also show how to check the assumption that the outcome would otherwise have been poor, and how to do a sensitivity analysis. We apply these methods to a clinical trial comparing initial angioplasty with medical management in patients with angina. We find that the initial benefit of a single angioplasty in reducing angina tends to disappear with time, but a policy of additional interventions as required yields a benefit that is maintained over 4 years. Such methods may be of interest to many pragmatic randomized trials in which the effects of the initial randomized treatments and the effects of the overall treatment strategies as implemented are both of interest.

Adult↗
PubMed2002

Coping with missing data in clinical trials: a model-based approach applied to asthma trials.

In most clinical trials, some patients do not complete their intended follow-up according to protocol, for a variety of reasons, and are often described as having 'dropped out' before the conclusion of the trial. Their subsequent measurements are missing, and this makes the analysis of the trial's repeated measures data more difficult. In this paper we briefly review the reasons for patient drop-out, and their implications for some commonly used methods of analysis. We then propose a class of models for modelling both the response to treatment and the drop-out process. Such models are readily fitted in a Bayesian framework using non-informative priors with the software BUGS. The results from such models are then compared with the results of standard methods for dealing with missing data in clinical trials, such as last observation carried forward. We further propose the use of a time transformation to linearize an asymptotic pattern of repeated measures over time and therefore simplify the modelling. All these ideas are illustrated using data from a five-arm asthma clinical trial.

Asthma↗