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PubMed2006

A survey of laboratory and statistical issues related to farmworker exposure studies.

Developing internally valid, and perhaps generalizable, farmworker exposure studies is a complex process that involves many statistical and laboratory considerations. Statistics are an integral component of each study beginning with the design stage and continuing to the final data analysis and interpretation. Similarly, data quality plays a significant role in the overall value of the study. Data quality can be derived from several experimental parameters including statistical design of the study and quality of environmental and biological analytical measurements. We discuss statistical and analytic issues that should be addressed in every farmworker study. These issues include study design and sample size determination, analytical methods and quality control and assurance, treatment of missing data or data below the method's limits of detection, and post-hoc analyses of data from multiple studies. Key words: analytical methodology, biomarkers, laboratory, limit of detection, omics, quality control, sample size, statistics.

Agriculture↗

PubMed1997

Empirical modeling of an in vitro activity of polychlorinated biphenyl congeners and mixtures.

The goal of this research is to predict an in vitro activity of polychlorinated biphenyl (PCB) congeners and their mixtures and to describe the relationship between this activity and chemical structure. The test system used multiple PCB concentrations on each cell culture plate in a repeated measures design, which improved precision for comparing between concentration levels. A weighted regression that accounted for this experimental design feature was used in fitting a nonlinear dose-response exponential model to the PCB concentration-activity data from an in vitro test system in which 3H-phorbol ester binding was measured in cerebellar granule cells exposed to different PCB congeners to test for their effects on protein kinase C translocation. The model allowed for the minimum level to be less than control, a common slope, and the estimation of the log of the concentration that produces an activity 50% above the control activity (E50) for 36 congeners and 3 commercial mixtures. Next, a weighted logistic regression using a second order response model in the variables Clortho, Clpara, and Clmeta was used to relate the estimated log E50s to indicators of chemical structure. This model was preferred over models that might seem more mechanistically based because in internal validation, it attained a smaller PRESS statistic (the sum of squares between all observed and predicted observations) than other models. Evidently, this second order model makes more efficient use of parameters than other models considered. Plots of the predictions of the logistic second order response model versus log Kow confirm the usual pattern that congeners with intermediate levels of log Kow are the more active. The data of three commercial mixtures were included in this regression by assuming a common combination index (ratio of observed E50 to predicted E50, assuming dose addition). The logistic model suggests that congeners with one, two, or three chlorine substitutions at the ortho position are more active than other congeners. Also, congeners with log Kow between 5.2 and 6.6 are generally more active. The estimated combination index indicated that the joint action of PCB congeners in the three commercial mixtures was less than dose additive. The error sum of squares was significantly large, which may indicate a lack of fit of the logistic model. Empirical Bayes estimates (EBE) are weighted averages of model predictions and observations of E50s and can be better estimates than the fitted model when there is a lack of fit. The PRESS statistic for the EBE indicated larger prediction error than for the logistic model, but the EBE provided better estimates of commercial mixture E50s based on dose addition. This may indicate that the logistic model is not incorporating all the information in the single congener data needed to predict mixtures.

Animals↗

PubMedDate not supplied

Causality and control: key to the experiment.

The main aim of the experimental approach in research is to discover causal relationships between variables. This article describes the concept of causality and discusses common and important aspects and factors related to causality, manipulation and control. The four principles which underpin the inference of causality in experiments are highlighted and the role of 'control' in achieving the aim of experimental studies is discussed. Some methods of control such as manipulation, randomization, matching subjects, and holding extraneous variables constant are considered. Experimental designs are underpinned by these concepts. Indication is given of the threats to internal validity, which will be discussed in detail in the next article in this series.

Causality↗

PubMed2006

Can a urinary tract symptom score predict the development of postoperative urinary retention in patients undergoing lower limb arthroplasty under spinal anaesthesia? A prospective study.

INTRODUCTION: There is no general consensus amongst orthopaedic surgeons on how best to manage the urinary tract and its complications after lower limb arthroplasty. This prospective audit investigates whether postoperative urinary retention can be predicted pre-operatively using the validated International Prostate Symptom Severity score (IPSS). PATIENTS AND METHODS: A total of 182 patients undergoing lower limb arthroplasty under spinal anaesthetic were given the IPSS questionnaire to complete pre-operatively and an audit into numbers catheterised postoperatively was performed. RESULTS: Overall, 69% of males and 39% of females required catheterisation. Following logistic regression analysis there was 0.85 predicted probability that males over 70 years would require catheterisation. The IPSS score was not useful in predicting retention in either sex at any age. CONCLUSIONS: We propose that all males over 70 years undergoing this type of surgery should be catheterised pre-operatively and all other patients should be catheterised postoperatively with close monitoring of bladder volumes to prevent established urinary retention.

Aged↗

PubMed2003

Pharmacologic treatment of poststroke depression: a systematic review of the literature.

UNLABELLED: CLINICAL QUESTION/OBJECTIVE: A systematic evaluation of the literature published from 1966 until December 2001 on pharmacologic interventions for poststroke depression (PSD). DESIGN: Articles were selected from a computer-based search and were independently reviewed by three evaluators using a standardized criteria including internal validity items as well as descriptive and quantitative items. RESULTS: Fifty studies were preliminarily reviewed and 10 randomized controlled trials (RCTs) were included for systematic analysis. CONCLUSION: Selective serotonin reuptake inhibitors (citalopram and fluoxetine) may be effective in the treatment of PSD. There is some evidence for a beneficial effect of the tricyclic antidepressant nortriptyline, however, the RCTs for this medication lack sufficient validity, and reports on side effects are contradictory.

Antidepressive Agents↗

PubMed2006

Behavioral treatment of challenging behaviors in individuals with mild mental retardation: meta-analysis of single-subject research.

A meta-analytic study on effectiveness of behavioral and psychotherapeutic treatments for challenging behaviors in individuals with mild mental retardation is reported. Eighty articles were examined. For each comparison, several study variables and two effect sizes (percentage of nonoverlapping data-PND and percentage of zero data-PZD) were evaluated (Ms = 75% and 35%, respectively). Studies in which experimental designs and methods of experimental functional analysis were used had significantly larger PNDs than those with AB designs and descriptive methods, respectively. Functional analysis, reliability of recording, generalization, and internally valid designs resulted in larger PZDs. We found that behavioral interventions for challenging behaviors are effective with people with mild mental retardation.

Humans↗

PubMed2005

Migration and relationship power among Mexican women.

Our study drew on original data collected in Durham, NC, and four sending communities in Mexico to examine differences in women's relationship power that are associated with migration and residence in the United States. We analyzed the personal, relationship, and social resources that condition the association between migration and women's power and the usefulness of the Relationship Control Scale (RCS) for capturing these effects. We found support for perspectives that emphasize that migration may simultaneously mitigate and reinforce gender inequities. Relative to their nonmigrant peers, Mexican women in the United States average higher emotional consonance with their partners, but lower relationship control and sexual negotiation power. Methodologically, we found that the RCS is internally valid and useful for measuring the impact of resources on women's power. However, the scale appears to combine diverse dimensions of relationship power that were differentially related to migration in our study.

Acculturation↗

PubMed2001

Management of acute exacerbations of COPD: a summary and appraisal of published evidence.

STUDY OBJECTIVES: To critically review the available data on the diagnostic evaluation, risk stratification, and therapeutic management of patients with acute exacerbations of COPD. DESIGN, SETTING, AND PARTICIPANTS: English-language articles were identified from the following databases: MEDLINE (from 1966 to week 5, 2000), EMBASE (from 1974 to week 18, 2000), HealthStar (from 1975 to June 2000), and the Cochrane Controlled Trials Register (2000, issue 1). The best available evidence on each subtopic then was selected for analysis. Randomized trials, sometimes buttressed by cohort studies, were used to evaluate therapeutic interventions. Cohort studies were used to evaluate diagnostic tests and risk stratification. Study design and results were summarized in evidence tables. Individual studies were rated as to their internal validity, external validity, and quality of study design. Statistical analyses of combined data were not performed. MEASUREMENT AND RESULTS: Limited data exist regarding the utility of most diagnostic tests. However, chest radiography and arterial blood gas sampling appear to be useful, while short-term spirometry measurements do not. In terms of the risk of relapse and the risk of death after hospitalization for an acute exacerbation, there are identifiable clinical variables that are associated with these outcomes. Therapies for which there is evidence of efficacy include bronchodilators, corticosteroids, and noninvasive positive-pressure ventilation. There is also support for the use of antibiotics in patients with more severe exacerbations. Based on limited data, mucolytics and chest physiotherapy do not appear to be of benefit, and oxygen supplementation appears to increase the risk of respiratory failure in an identifiable subgroup of patients. CONCLUSIONS: Although suggestions for appropriate management can be made based on available evidence, the supporting literature is spotty. Further high-quality research is needed and will require an improved, generally acceptable, and transportable definition of the syndrome "acute exacerbation of COPD" and improved methods for observing and measuring outcomes.

Acute Disease↗

PubMed2001

Description of a generally applicable model for the evaluation of uncertainty of measurement in clinical chemistry.

There is a growing pressure on clinical chemistry laboratories to conform to quality standards that require the evaluation and expression of the uncertainty of results of measurement. Nevertheless, there is some reluctance to accept the uncertainty concept in the analytical community due to difficulty in evaluating uncertainty in practice. For example, often the uncertainty of some uncertainty components is not known very well in clinical chemistry measurements, such as those associated with matrix effects or with the values of the calibrators. Moreover, it is not clear how to interpret uncertainty in relation to diagnostic criteria, reference ranges and other decision limits in clinical chemistry practice. Hence, the value of reporting the uncertainty of the measurement result is not obvious. In this paper it is suggested a relatively simple, logical procedure for evaluating measurement uncertainty based on the principles in the Guide for the Expression of Uncertainty of Measurement (GUM). The measurement process is partitioned into elements that are well known to the analyst, namely sampling, calibration, and analysis. The corresponding model function expresses the result of a measurement as the value obtained by the analytical procedure multiplied by the correction factors for sampling bias, for bias caused by the calibrators, and for other types of bias. Under normal conditions, when the measurement procedure is validated and corrected for all known bias, the expected value of each correction factor is one. The uncertainty that remains with regard to sampling, manufacturing of calibrators and other types of bias is combined with the analytical imprecision to yield a combined uncertainty of a result of measurement. The advantages of this approach are: (i) Data from the method validation, internal quality control and from participation in external quality control schemes can be used as input in the uncertainty evaluation process. (ii) The partition of the measurement into well-defined tasks highlights the different responsibilities of the clinical chemistry laboratory and of the manufacturer of reagents and calibrators. (iii) The approach can be used to harmonize the uncertainty evaluation process, which is particularly relevant for laboratories seeking accreditation under ISO 17025. The application of the proposed model is demonstrated by evaluating the uncertainty of a result of a measurement of prolactin in human serum. In the example it is shown how to treat the uncertainty associated with a calibrator supplied with a commercial analytical kit, and how to evaluate the uncertainty associated with matrix effects.

Bias↗

PubMed1984

Content and effects of alcohol advertising: comment on NTIS pub. no. PB82-123142.

Atkin and Block's study on the content and effects of alcohol advertising is discounted. The substudies involved in the research are described and their methodologies are criticized. Weaknesses are found in the following areas: coding procedures; definitions and interpretations of categories of advertising content; sampling procedures; and measures of exposure to advertising. It is felt that causal interpretations from such weak measures should not be made. The diversity of research methods used is deemed commendable. However, since all of the substudies use the same basic sample, it is of little surprise that convergent evidence results. Also, since all research methods used are felt to be inadequate, such convergence does not necessarily show external and internal validity.

Advertising↗

PubMed1993

Alcohol surveys with high and low coverage rate: a comparative analysis of survey strategies in the alcohol field.

Two Swedish alcohol surveys were compared in a search for a reasonable explanation of the large difference in their coverage rates, namely 75% and 28%. In many respects both surveys conducted in the late 1980s by large, well-known institutes, are of a similar type with rather large samples of Swedes. The technique used in the survey with a very high coverage rate (Survey A) takes into consideration the actual drinking pattern of the population studied (i.e., the concentration of drinking on weekends). By dividing a "normal week's consumption" into four units (Monday-Thursday, Friday, Saturday and Sunday), the technique allows one to average periods with varying drinking habits. In the survey with a low coverage rate (Survey B) a "normal week's consumption" was not so divided. A test of internal validity within Survey A underlined the general finding that its higher coverage rate was due to this division. A test of the external validity at aggregate level did not support assumptions about "telescoping" effects in A. Both A and B had a normal week as a basis of measurement for investigating typical drinking habits. The literature concerning differences in coverage rates focuses on the measurement of modal habits versus mean habits. The main explanation of differences is that methods that focus on modal habits (i.e., the Quantity-Frequency Scale) generate a lower coverage rate than do methods that elicit the arithmetic mean (i.e., the last-week recall). Since A and B both belong to the former type of scale, this does not explain our results.

Adolescent↗

PubMed1996

The Driving Expectancy Questionnaire: development, psychometric assessment and predictive utility among young drink-drivers.

OBJECTIVE: The primary objective of this research was to develop a Driving Expectancy Questionnaire (DEQ) that reflects a model in which a distinction is made between driving skill and driving style. The second objective was to study young drivers across the spectrum of drink-driving practices, from non-drivers to convicted drink-drivers, and to examine the relationship between their expectancies about driving and their drink-driving practices. METHOD: The data from two separate samples, recruited through availability sampling, were used for the purpose of exploratory (n = 224; 122 men) and confirmatory factor analyses (n = 191; 101 men), respectively. RESULTS: The results revealed two factors of expectancies, driving skill and driving style, supporting the proposed model. The reliability, internal validity and relative independence of the factors were largely confirmed. Furthermore, criterion-related validity was demonstrated: expectancies about driving varied with drink-driving practices. Expectancies also contributed additional predictive power in relation to drink-driving practices beyond that afforded by several well-validated variables. CONCLUSIONS: The results are encouraging in terms of the ability of the DEQ to identify individual differences in expectancies about driving skill and driving style that are closely related to variations in drink-driving practices. The practical implications of these findings, as well as the potential research possibilities, are discussed.

Adolescent↗

PubMed2002

Randomized versus nonrandomized studies of alcohol treatment: participants, methodological features and posttreatment functioning.

OBJECTIVE: Randomized trials are widely acknowledged to be the most rigorous method to estimate the comparative efficacy of treatments. Concerns have been raised, however, about the generalizability of findings from randomized trials of alcohol treatments to actual treatment circumstances, and about the internal validity of randomized trials. The purpose of this review was to compare the participants, methodological features and posttreatment functioning in randomized and nonrandomized studies of alcohol treatment. METHOD: Using systematic literature search techniques, 232 randomized and 92 nonrandomized trials published between 1970 and 1998 were identified. Each investigation was scored on a methodological quality scale, participant characteristics were recorded and participants' follow-up abstinence and improvement rates were calculated. RESULTS: Randomized investigations were more likely to use participant selection criteria, to use recognized diagnostic criteria to characterize participants and to stringently implement treatment and assess outcomes. Nonrandomized investigations were more likely to assess outcomes in higher proportions of participants over longer follow-up periods and to have greater statistical power t o detect treatment effects. Abstinence and improvementrates following active treatment were similar for the two types of design (proportion abstinent: 0.35 and 0.39, and proportion improved: 0.52 and 0.54, for randomized and nonrandomized trials, respectively), even when differences in study features were controlled. CONCLUSIONS: The contrasting strengths and weaknesses of randomized and nonrandomized studies suggest that they should be considered as complementary forms of treatment evaluation, in the alcohol treatment field and perhaps more generally.

Alcoholism↗

PubMed2002

Treating alcohol problems with self-help materials: a population study.

OBJECTIVE: An experimental trial was used to assess the effectiveness of a self-help book and a personalized assessment-feedback intervention, both separately and in combination with each other, in a general population survey. METHOD: Participants (N = 86; 66.3% male) were recruited through a random digit dialing telephone survey conducted by the Centre for Addiction and Mental Health, Toronto, Ontario, Canada. Respondents were randomly assigned to one of four conditions in a two-by-two factorial design: "no-intervention" control group, "personalized feedback only," "self-help book only" and "both personalized feedback and self-help book." Respondents were followed up in 6 months' time, and differences in drinking status were compared between experimental conditions using a multivariate analysis of covariance with baseline drinking severity as the covariate. RESULTS: Support was provided for an interaction hypothesis in which respondents who received both interventions reported significantly improved drinking outcomes at 6-month follow-up, compared with respondents who received just one of the interventions or who received no intervention. CONCLUSIONS: Because respondents were recruited from a representative sample of the general population into a randomized trial with a no-intervention control group, this research design maximized both external and internal validity in examining the effectiveness of self-help interventions.

Alcohol Drinking↗

PubMed2005

Cross-cultural adaptation of the quality of life assessment scale on Alzheimer disease.

OBJECTIVE: To present the internal validation of the quality of life (QOL) evaluation scale for patients with Alzheimer's disease (AD) and their caregivers/family members, proposed by Logsdon et al. METHOD: The scale was adapted through translation, back translation and equivalence evaluation. The Portuguese version was administered to a sample of 40 patients with mild to moderate AD according to NINCDS ADRDA and DSM-III-R criteria, and also to their respective caregivers/family members. RESULTS: The reliability of the instrument was excellent, both in the intra and the inter-examiner test-retest. The correlation coefficients for the intra-examiner assessment were 0.87/0.95/0.95 (p < 0.001)) for the patient, family and caregiver versions, respectively. The correlation coefficients for the inter-examiner assessment were 0.76/0.96/0.93 (p < 0.001) for the patients, family and caregiver versions, respectively. The reliability was excellent for both the patient and the relatives' versions in relation to the patient's QOL (alpha = 0.81 and 0.85, respectively), and also in relation to the caregiver's QOL (alpha = 0.84). CONCLUSION: The adapted version of the instrument proved to be straightforward and brief, presenting excellent stability and reliability. The Portuguese version can be obtained by contacting the first author.

Adult↗

PubMed2005

[Participatory evaluation in health programs: a proposal for the Adolescent Health Care Program].

This article presents a model for participatory evaluation of the Adolescent Health Program (PROSAD) in Brazil. The study focuses on the concept of participation, with a review of internationally validated planning methodologies (RAP, logFRAME, ZOPP, PCM) and the programmatic characteristics of PROSAD. The proposed model comprises 4 steps, involving the constitution of the analytical matrix, a self-evaluation workshop, a summary of results, and graphic representation. The model promotes participatory practice in health program management by using techniques that allow a workshop to be held in 70 minutes (mean time), producing results that are recognized and easily grasped by the local team.

Adolescent↗

PubMed2000

Efficacy in treatment of subclinical cervical HPV infection without intraepithelial neoplasia: systematic review.

CONTEXT: The treatment of the subclinical Human papillomavirus (HPV) infection of the uterine cervix is controversial. OBJECTIVE: To assess the efficacy of any therapy for subclinical HPV infection of the cervix without intraepithelial neoplasia, via a search in the medical literature. METHOD: We performed a systematic review with a comprehensive reference search in Medline, LILACS, Excerpta Medica, AIDSLINE, Popline, Cochrane Library and other authors' reference lists to identify experimental studies of therapy for subclinical HPV infection without intraepithelial neoplasia of the uterine cervix. In order to identify unpublished studies, we also contacted experts in the area, clinical trial registries, pharmaceutical industries, government and research institutions. We also searched on the Internet and in the book-of-abstracts of some medical conferences. The studies identified were masked and selected by inclusion criteria to help ascertain their internal validity. The data about regression or progression of HPV infection were extracted from the studies included. RESULTS: We identified 67 studies related to the treatment of subclinical HPV infection without intraepithelial neoplasia of the uterine cervix. Only five clinical trials matched the inclusion criteria and none demonstrated significant differences between the experimental group and the control group concerning regression of HPV infection (with or without CIN I) or progression to higher grades of CIN. CONCLUSION: The evidence we found in the medical literature regarding the efficacy of any therapy for subclinical HPV infection without intraepithelial neoplasia of the uterine cervix was unsatisfactory.

Clinical Trials as Topic↗

PubMed2004

Evidence from clinical trials: can we do better?

Randomized clinical trials provide the most internally valid evidence for medical decision-making. In many areas of neurology, results from clinical trials showing which therapies are and are not effective have had a substantial impact on patient care. Relative to observational methods, the central advantage of clinical trials is control of bias attributable to unmeasured differences between patients. However, trials also have clear limitations, including a historical failure to include a representative cross-section of patients with a given disease, and highly structured treatment regimes that are difficult to replicate in normal practice settings. These limitations tend to reduce the generalizability of results from clinical trials. This article reviews some ways in which the design and application of clinical trials could be improved so that the evidence produced would be more relevant to health-care providers and other decision makers.

Biomedical Research↗