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Biomedical subjects

D G Altman

Publications and source records attributed to D G Altman.

At least 127 records · Page 7Linked to original sources
PubMed1996

Tobacco promotion and susceptibility to tobacco use among adolescents aged 12 through 17 years in a nationally representative sample.

OBJECTIVES: The purpose of this study was to examine whether youth participation in tobacco promotion campaigns is associated with susceptibility to tobacco use. METHODS: Data were collected from telephone interviews of a national random sample of 1047 adolescents 12 to 17 years of age. RESULTS: A proportional odds model was used to estimate the effects of age, gender, presence of a tobacco user in the household, awareness of tobacco promotions, knowledge of a young adult or adolescent friend owning a promotional item, participation in tobacco promotions, and receipt of free tobacco samples or direct mail from tobacco companies on susceptibility to tobacco use. All of the covariates, except for receiving direct mailings and knowing a young adult friend who owned a promotional item, were significantly associated with susceptibility. CONCLUSIONS: There is a strong association between an awareness of and involvement with tobacco promotions and being susceptible to tobacco use or a user of tobacco products.

Adolescent↗
PubMed1995

Estimating sample sizes for binary, ordered categorical, and continuous outcomes in two group comparisons.

Sample size calculations are now mandatory for many research protocols, but the ones useful in common situations are not all easily accessible. This paper outlines the ways of calculating sample sizes in two group studies for binary, ordered categorical, and continuous outcomes. Formulas and worked examples are given. Maximum power is usually achieved by having equal numbers in the two groups. However, this is not always possible and calculations for unequal group sizes are given.

Data Interpretation, Statistical↗
PubMed1995

Comparing methods of measurement: why plotting difference against standard method is misleading.

When comparing a new method of measurement with a standard method, one of the things we want to know is whether the difference between the measurements by the two methods is related to the magnitude of the measurement. A plot of the difference against the standard measurement is sometimes suggested, but this will always appear to show a relation between difference and magnitude when there is none. A plot of the difference against the average of the standard and new measurements is unlikely to mislead in this way. We show this theoretically and by a practical example.

Bias↗
PubMed1995

The methodologic quality of randomization as assessed from reports of trials in specialist and general medical journals.

OBJECTIVE: To assess the quality of randomization from reports of trials in a sample of specialist journals, and to compare those results with a similar assessment from a sample of general medical journals. DESIGN: Evaluation of all 206 reports of parallel-group randomized trials published in the 1990 and 1991 volumes of four journals of obstetrics and gynecology and of 81 reports of trials published during 1987 in four general medical journals. RESULTS: Of the reports published in the specialist and in the general medical journals, only 32% and 48%, respectively, reported having used an adequate method to generate random numbers; only 23% and 26%, respectively, contained information showing that steps had been taken to conceal assignment until the point of treatment allocation; and merely 9% and 15%, respectively, described adequate methods of both sequence generation and allocation concealment. In those reports of trials that had apparently used unrestricted randomization, the differences in sample sizes between treatment and control groups were much smaller than would be expected by chance, and that feature was more marked in the specialist journals. In reports of trials in which hypothesis tests had been used to compare baseline characteristics, only 2% of tests reported in specialist journals and 4% of tests reported in general journals were statistically significant, lower than the expected rate of 5%. CONCLUSIONS: Generating unbiased comparison groups requires proper randomization, yet the reports in these specialist and general journals usually provided inadequate or unacceptable information. Additional analyses suggest that nonrandom manipulation of comparison groups and selective reporting of baseline comparisons may have occurred.

Gynecology↗
PubMed1995

Empirical evidence of bias. Dimensions of methodological quality associated with estimates of treatment effects in controlled trials.

OBJECTIVE: To determine if inadequate approaches to randomized controlled trial design and execution are associated with evidence of bias in estimating treatment effects. DESIGN: An observational study in which we assessed the methodological quality of 250 controlled trials from 33 meta-analyses and then analyzed, using multiple logistic regression models, the associations between those assessments and estimated treatment effects. DATA SOURCES: Meta-analyses from the Cochrane Pregnancy and Childbirth Database. MAIN OUTCOME MEASURES: The associations between estimates of treatment effects and inadequate allocation concealment, exclusions after randomization, and lack of double-blinding. RESULTS: Compared with trials in which authors reported adequately concealed treatment allocation, trials in which concealment was either inadequate or unclear (did not report or incompletely reported a concealment approach) yielded larger estimates of treatment effects (P < .001). Odds ratios were exaggerated by 41% for inadequately concealed trials and by 30% for unclearly concealed trials (adjusted for other aspects of quality). Trials in which participants had been excluded after randomization did not yield larger estimates of effects, but that lack of association may be due to incomplete reporting. Trials that were not double-blind also yielded larger estimates of effects (P = .01), with odds ratios being exaggerated by 17%. CONCLUSIONS: This study provides empirical evidence that inadequate methodological approaches in controlled trials, particularly those representing poor allocation concealment, are associated with bias. Readers of trial reports should be wary of these pitfalls, and investigators must improve their design, execution, and reporting of trials.

Bias↗
PubMed1995

Randomised consent designs in cancer clinical trials.

In 1977, Zelen proposed a new design for clinical trials with the aim of increasing recruitment by avoiding some of the problems associated with obtaining informed consent. These 'randomised consent' designs have proved controversial, and have not often been used. This paper explains the statistical aspects of single and double randomised consent designs and reviews some of the ethical issues. All identified published cancer treatment trials using a randomised consent design are considered in some detail. Reasons for and against the use of these designs are summarised.

Ethics, Medical↗
PubMed1995

Sustaining interventions in community systems: on the relationship between researchers and communities.

Important goals of research-based community interventions include the long-term maintenance of effects and fostering of collaboration between researchers and community leaders. This article reviews the challenges associated with transferring innovations to community systems, changing program delivery from an experimental context controlled by researchers to program delivery controlled by community organizations, and sustaining long-term effects of interventions. It is suggested that researchers who develop and implement community interventions in diverse health areas need to confront several issues: (a) fostering effective long-term relationships between researchers and the communities they study and in which they intervene and (b) designing and implementing interventions that are useful to community systems after the formal phase of research ends.

California↗
PubMed1995

Assessment of and intervention for psychosocial problems in routine oncology practice.

An audit was carried out of 51 oncology patients referred to a clinical psychology service to identify the characteristics of patients selected for referral and to assess change following psychological intervention. A survey was conducted of an unselected sample of oncology patients representative of the workload of the oncology department from which the referrals came, to determine the prevalence of comparable psychosocial problems among patients who were not referred for help and to assess whether doctors were aware of the problems patients reported. Data were collected using the Hospital Anxiety and Depression (HAD) and Mental Adjustment to Cancer (MAC) scales and a problem checklist devised for this study. Referred patients were significantly more anxious and depressed (P < 0.001) and showed poorer adjustment on MAC scales than the surveyed sample, but 30% of the latter group warranted assessment for anxiety and 23% for depression. The number of psychosocial problems of their severity. Intervention was clinically significant mood disorder irrespective of the specific problems of their severity. Intervention was associated with a significant improvement in distress and problems for referred patients by the time of discharge. Psychosocial problems were often undetected by staff even in referred patients. The checklist is a feasible screening method for potentially remediable problems which are cumulatively a significant contributor to cancer patients' distress.

Adaptation, Psychological↗
PubMed1995

Review of survival analyses published in cancer journals.

Survival analysis has found widespread applications in medicine in the last 10-15 years. However, there has been no published review of the use and presentation of survival analyses. We have carried out a systematic review of the research papers published between October and December 1991 in five clinical oncology journals. A total of 132 papers were reviewed. We looked at several aspects of study design, data handling, analysis and presentation of the results. We found that almost half of the papers did not give any summary of length of follow-up; that in 62% of papers at least one end point was not clearly defined; and that both logrank and multivariate analyses were frequently reported at most only as P-values [63/84 (75%) and 22/47 (47%) respectively]. Furthermore, although many studies were small, uncertainty of the estimates was rarely indicated [in 13/84 (15%) logrank and 16/47 (34%) multivariate results]. The procedure for categorisation of continuous variables in logrank analyses was explained in only 8/49 (16%) papers. The quality of graphs was felt to be poor in 43/117 (37%) papers which included at least one survival curve. To address some of the presentational inadequacies found in this review we include new suggested guidelines for the presentation of survival analyses in medical journals. These would complement the statistical guidelines recommended by several clinical oncology journals.

Analysis of Variance↗
PubMed1995

Repeatability of measurement of fetal nuchal translucency thickness.

The aim of this prospective study was to assess the repeatability of measurement of fetal nuchal translucency thickness at 10-14 weeks' gestation. The nuchal translucency was measured by two of four operators in 200 pregnant women attending the Harris Birthright Research Centre for Fetal Medicine at 10-14 weeks' gestation. To assess repeatability of different components of variability, six measurements of nuchal translucency were made on each fetus, with a total of 1200 measurements. The data of this study demonstrate that 95% of the time the intraobserver, interobserver and caliper placement repeatability of measuring fetal nuchal translucency were less than 0.54 mm, 0.62 mm and 0.58 mm, respectively. In addition, the repeatability was unrelated to the size of the nuchal translucency. The findings of this study demonstrate that, when the nuchal translucency thickness is measured by well-trained operators, the measurement is highly reproducible.

Chromosome Aberrations↗