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PubMed1997

Empowering research: statistical power in general practice research.

BACKGROUND: Statistical power is a measure of the extent to which a study is capable of discerning differences or associations which exist within the population under investigation, and is of critical importance whenever a hypothesis is tested by statistics. Conventionally, studies should reach a power level of 0.8, such that four times out of five a false null hypothesis will be rejected by a study. Statistical power may most easily be increased by increasing sample size. OBJECTIVE: We aimed to assess the level of statistical power of general practice research. METHODS: A total of 1422 statistical tests in 85 quantitative original papers in the British Journal of General Practice were analysed for statistical power. RESULTS: The median power of tests analysed was 0.71, representing a slightly greater than two-thirds likelihood of rejecting false null hypotheses. Of 85 studies, 37 (44%) attained power of 0.8 or more. Ten studies had power of more than 0.99 suggesting 'over-powering'. Twenty-one of the papers surveyed (25%) had a likelihood of gaining significant results poorer than that obtained by tossing a coin when a null hypothesis is false. CONCLUSION: While achieving higher power than studies in similar surveys of other disciplines, the power of general practice research falls short of the 0.8 convention. Adequate power is essential so that effects which exist are not missed. Recommendations are made concerning power calculations prior to the start of research and reporting of results in journal articles.

Bias↗
PubMed2002

Group interviews in primary care research: advancing the state of the art or ritualized research?

BACKGROUND: Focus groups have become an important data gathering technique in primary care research. OBJECTIVES: This study provides an integrated review of recent articles that used focus groups as a data collection method to gather information from family physicians. METHODS: Medline was searched for articles that used focus groups with family physicians in a North American setting during the 1990s. Articles that met this criteria were critically evaluated to determine who participated, the number of groups conducted, setting, length, inclusion and exclusion criteria, sampling technique and whether the groups were used as part of a larger study. RESULTS: The twenty articles discussed herein revealed tremendous variation in how focus group research is conducted and reported. CONCLUSIONS: Focus group research is a popular form of qualitative research in primary care research. Journals reporting qualitative research should require that certain basic information be present, thereby advancing the state of the art and permitting readers to better evaluate these articles.

Canada↗
PubMed2002

Qualitative research and the problem of judgement: lessons from interviewing fellow professionals.

BACKGROUND: Qualitative research methods are recognized increasingly as valuable tools for primary care research, and add an extra dimension to quantitative work. OBJECTIVE: The aim of this study was to illustrate the benefits and problems attending the dual role of clinician/qualitative researcher. METHODS: As part of two studies employing semi-structured interviews of GPs in a North-West conurbation, about the topics of consultations on chronic low back pain and drug misuse in primary care, respondents' views on their interaction with a GP researcher were explored. RESULTS: Access to the GP by the interviewing GP was easier when the GP researcher was known to the respondent. Such prior knowledge, however, may then influence the content of the data and the manner in which the GP researcher is perceived. During the interview itself, where respondents recognized the researcher as a clinician, interviews were broader in scope and provided richer and more personal accounts of attitudes and behaviour in clinical practice. The GP was also identified as an expert and judge, not just of clinical decision making but also about moral judgements made by GPs in their work. This will impact on the data obtained at interview and must be taken into consideration when the data are interpreted and analysed. CONCLUSION: Qualitative research techniques increasingly are advocated as appropriate for research on and in general practice. The professional identity of the researcher plays an important part in constructing the kind of data obtained in such studies, and this must be made apparent in reporting and discussions of such qualitative work.

Effect Modifier, Epidemiologic↗
PubMed1996

Social support in the context of caregiving: husbands' provision of support to wives involved in parent care.

The purpose of this study was to identify ways in which social support is related to the caregiving stress and well-being experienced by adult daughter caregivers. The study focused on a specific source of support, caregivers' husbands, and included reports from 126 caregivers and their husbands. Main and buffering effects of four types of support (emotional and instrumental support provided to the caregiver and to her parent) were tested, and caregiver's level of optimism was controlled. Results were similar for caregivers' and husbands' accounts of support. Buffering effects were found only for physical health, whereas effects opposite those predicted by the buffering hypothesis were detected for positive affect. A main effect was found in nearly all analyses of marital satisfaction. No main or buffering effects of support were detected for depression. Findings highlight the complexity of supportive exchanges by illustrating the simultaneous operation of different types of support and their distinctive impact on the caregiving stress and well-being relationship.

Adult↗
PubMed1989

On randomized controlled trials and lifestyle interventions.

Randomized controlled trials (RCT) are viewed as the ultimate method for evaluation. The author claims that RCT do not enable full evaluation of lifestyle interventions in particular. Lifestyle interventions usually affect several diseases not measured by RCTs and the people who have undergone these interventions also have an impact on the lifestyle in their immediate environment. These potential biases indicate that RCTs underestimate the value of lifestyle interventions.

Bias↗
PubMed1994

Statistical modelling and prediction of lung cancer mortality in the Czech and Slovak Republics, 1960-1999.

BACKGROUND: The aim of the study was to analyse the pattern of lung cancer mortality from 1960 to 1989 and to predict lung cancer mortality for 1990-1999 for males and females aged > or = 30 years in the Czech and Slovak Republics. METHOD: The mortality pattern of lung cancer was examined and predicted using republic-age-period-cohort models. RESULTS: Trends in lung cancer mortality were upward for both sexes over the study period. In the early 1960s, lung cancer mortality in Slovak males was much lower than that in Czech males, but since the late 1960s lung cancer mortality in males increased more rapidly in Slovakia than in the Czech Republic. It was predicted that mortality due to lung cancer in Slovak males would exceed that in Czech males during the last 5 years of the 20th century. Slovak female lung cancer mortality was lower than that for Czech females throughout the study period, and the trends in both republics were similar.

Adult↗
PubMed1994

Is Trichomonas vaginalis a cause of cervical neoplasia? Results from a combined analysis of 24 studies.

BACKGROUND: We conducted this combined analysis of available data from studies with information on this issue to clarify the association between Trichomonas vaginalis infection and cervical neoplasia. METHODS: We performed MEDLINE searches (1966-1993) using the key words and phrases 'trichomonas vaginitis' and 'neoplasms, cervix' for articles published in English, and searched citations of the articles obtained from MEDLINE: A total of 24 articles (two cohort studies and 22 case-control) were included in this data analysis. In the analysis, the studies were evaluated for heterogeneity using Breslow-Day tests for homogeneity of the odds ratios and of rate ratios. If the odds ratios from studies are heterogeneous, it is not appropriate to combine them using the Mantel-Haenszel method. Also, publication bias was evaluated by assessing the association between the observed effect size and the variance of the effect size using a rank correlation test. RESULTS: The combined summary relative risk for the two cohort studies was 1.93 (95% confidence interval: 1.22-2.65) indicating an approximate doubling of the risk of cervical neoplasia in the presence of T. vaginalis infection. The attributable risks among exposed subjects and among the source population were 47.4% and 2.1% respectively. Results of the 22 retrospective studies were much less consistent. However, most of them demonstrated a significant positive association. CONCLUSIONS: This combined analysis suggests that there is an association between T. vaginalis and the risk of cervical neoplasia, but that such infections account for only 2% of cervical neoplasia.

Adolescent↗
PubMed1995

Differential response to early nutrition supplementation: long-term effects on height at adolescence.

BACKGROUND: The classical risk approach to predicting who benefits from an intervention is unsound because it relies on the theoretical assumption that those at risk will necessarily benefit. A better approach to systematically test who benefits from nutrition supplementation is proposed using interactive models. METHODS: Differential effects of nutrition supplementation during early childhood on stature at adolescence were studied in 245 males and 215 females to identify determinants of long-term benefit from food supplementation. Factors studied included family socioeconomic status (SES) and children's home diet and diarrhoea during the first 3 years of life. To determine whether a factor conferred benefit, the statistical significance of the interaction between this factor and the intervention was tested. Data from the INCAP supplementation trial in Guatemala and from the follow-up of the same subjects at adolescence were used. RESULTS: Ordinary least squares (OLS) showed that high rates of diarrhoea in males and poor SES in females were significant determinants of benefit from supplementation at adolescence, and that the effects were mediated by length at 3 years old. Results of two-stage least squares (2SLS) analysis showed that length at 36 months, maturation and maternal height were significant determinants of height at adolescence but SES was not. CONCLUSIONS: Nutrition supplementation in early childhood has long-lasting effects on body size and the larger benefits acquired by some groups of children remain throughout early adulthood. The relevance of these findings for screening and targeting of nutritional interventions is discussed.

Adolescent↗
PubMed1996

Sudden infant death syndrome: insulation from bedding and clothing and its effect modifiers. The National Cot Death Study Group.

BACKGROUND: Thermal stress related to excessive insulation from bedding and clothing has been postulated to be associated with sudden infant death syndrome (SIDS). METHODS: The parents of 393 (81%) of the infants who died of SIDS in the post neonatal period were interviewed at home. Interviews were also completed with the parents of 1592 (88.4% of total) controls, a representative sample of all hospital births. The study was conducted in regions of the North and South Island of New Zealand in which 78% of all New Zealand births occurred in 1987-1990. Temperatures for the infant's bedroom estimated from the outside temperature and a model were used to predict the appropriate insulation for lower critical temperature (temperature below which the metabolic rate is likely to increase). RESULTS: Sudden infant death syndrome was associated with extra thermal insulation of > 2 tog above the lower critical value, the odds ratio (OR) was 1.70 (95% confidence interval [Cl] : 1.3-2.20) after adjusting for season. After adjusting for a number of confounding factors the CR was reduced to 1.35 (95% Cl: 0.97-1.87). Also associated with SIDS was too little thermal insulation OR = 1.67(95% Cl: 1.13-2.48; and 2.63 (95% Cl: 1.61-4.30) when adjustments were made for the confounding factors. The interaction effect between infants sleeping prone and >2 tog extra thermal insulation was significant (OR = 6.07, 95% Cl: 3.83-9.60). Infants with too little thermal insulation were at increased risk if they were not tightly wrapped (OR = 3.81, 95% Cl: 2.04-7.09). There were also small additive interaction effects if the mother smoked and the infants had > 2 tog extra thermal insulation, or they were ill and had > 4 tog extra insulation. Interaction effects between thermal insulation and other factors were not significant. CONCLUSION: More thermal insulation than was necessary to maintain the lower critical temperature increased the risk of SIDS primarily among infants in the prone sleep position, and to a lesser degree in infants whose mothers smoked and in infants who were unwell.

Bedding and Linens↗
PubMed1996

Characteristics of non-insulin-dependent diabetes mellitus in elderly men: effect modification by family history.

BACKGROUND: Heredity, obesity and fat distribution may interact with each other in their association with diabetes risk. Therefore we tried to elucidate the role of familial diabetes as effect modifier in the association of obesity, glucose metabolism and lipoproteins with non-insulin-dependent diabetes mellitus. METHODS: A cross-sectional study was carried out among 468 elderly men. Within strata of family history, men with diabetes and normal glucose tolerance were compared with respect to anthropometry, characteristics of glucose metabolism and serum lipids. RESULTS: Of the participants, 14.5 percent were diabetic. In diabetic men a family history of diabetes occurred more often (22.1 percent) than in men with normal (6.8 percent, P < 0.001) or impaired glucose tolerance (8.5 percent). In diabetic men with a family history, the ratio of fasting insulin to glucose and the ratio of areas under the insulin and glucose curves during oral glucose tolerance testing were lower compared to men with normal glucose tolerance. In men without a family history, these differences were smaller (interaction P = 0.06). In diabetic men without a family history, fasting insulin levels were markedly elevated (P < 0.001), whereas in men with a family history there was only a slight elevation. The presence of a family history resulted in more severe deteriorations in lipids, especially in fasting triglycerides (interaction P = 0.075). No interaction between indices of obesity and a family history was observed. CONCLUSIONS: Our findings suggest that elderly diabetic men with a family history of diabetes represent a different subgroup than elderly men without such a history, characterized by larger deteriorations in indices for beta-cell function and higher triglyceride levels.

Aged↗
PubMed2002

Meat and dairy food consumption and breast cancer: a pooled analysis of cohort studies.

BACKGROUND: More than 20 studies have investigated the relation between meat and dairy food consumption and breast cancer risk with conflicting results. Our objective was to evaluate the risk of breast cancer associated with meat and dairy food consumption and to assess whether non-dietary risk factors modify the relation. METHODS: We combined the primary data from eight prospective cohort studies from North America and Western Europe with at least 200 incident breast cancer cases, assessment of usual food and nutrient intakes, and a validation study of the dietary assessment instrument. The pooled database included 351,041 women, 7379 of whom were diagnosed with invasive breast cancer during up to 15 years of follow-up. RESULTS: We found no significant association between intakes of total meat, red meat, white meat, total dairy fluids, or total dairy solids and breast cancer risk. Categorical analyses suggested a J-shaped association for egg consumption where, compared to women who did not eat eggs, breast cancer risk was slightly decreased among women who consumed < 2 eggs per week but slightly increased among women who consumed > or = 1 egg per day. CONCLUSIONS: We found no significant associations between intake of meat or dairy products and risk of breast cancer. An inconsistent relation between egg consumption and risk of breast cancer merits further investigation.

Animals↗
PubMed2002

Role of ancillary variables in the design, analysis, and interpretation of animal experiments.

During the course of an experiment using animals, many variables (e.g., age, body weight at several times, food and water consumption, hematology, and clinical biochemistry) and other characteristics are often recorded in addition to the primary response variable(s) specified by the experimenter. These additional variables have an important role in the design and interpretation of the experiment. They may be formally incorporated into the design and/or analysis and thus increase precision and power. However, even if these variables are not incorporated into the primary statistical design or into the formal analysis of the experiment, they may nevertheless be used in an ancillary or exploratory way to provide valuable information about the experiment, as shown by various examples. Used in this way, ancillary variables may improve analysis and interpretation by providing an assessment of the randomization process and an approach to the identification of outliers, lead to the generation of new hypotheses, and increase generality of results or account for differences in results when compared across different experiments. Thus, appropriate use of additional variables may lead to reduction in the number of animals required to achieve the aims of the experiment and may provide additional scientific information as an extra benefit. Unfortunately, this type of information is sometimes effectively discarded because its potential value is not recognized. Guidelines for use of animals include, in addition to the obligation to follow humane procedures, the obligation to use no more animals than necessary. Ethical experimental practice thus requires that all information be properly used and reported.

Animals↗
PubMed1996

Effects of Brazelton demonstrations on later parenting: a meta-analysis.

Meta-analysis of parenting interventions based on the Neonatal Behavioral Assessment Scale (NBAS) was conducted. Only published studies (n = 13) were included in this analysis, with one effect size entered for each study. The studies contained a total of 668 families, an average of about 51 per study. Effect sizes are reported in terms of the correlation coefficient (r) as well as the difference between experimental and control group means divided by the pooled standard deviation (Cohen's d). Analyses were conducted by weighting each study equally (unit weighting) and also by sample size. Similar average effect size were obtained for both weighting procedures (r's of about.2, d's of about.4), indicating that Brazelton-based interventions during the neonatal period have a small-moderate beneficial effect on the quality of later parenting. The probability of obtaining these findings by chance approached zero. The potential factors influencing these results are discussed, as well as directions for future research.

Effect Modifier, Epidemiologic↗
PubMedDate not supplied

Post-hoc probing of significant moderational and mediational effects in studies of pediatric populations.

OBJECTIVE: To provide examples of post-hoc probing of significant moderator and mediator effects in research on children with pediatric conditions. METHODS: To demonstrate post-hoc probing of moderational effects, significant two-way interaction effects (dichotomous variable x continuous variable; continuous variable x continuous variable) were probed with regressions that included conditional moderator variables. Regression lines were plotted based on the resulting regression equations that included simple slopes and y-intercepts. To demonstrate probing of mediational effects, the significance of the indirect effect was tested (i.e., the drop in the total predictor --> outcome effect when the mediator is included in the model), using Sobel's (1988) equation for computing the standard error of the indirect effect. RESULTS: All significant moderator and mediator effects are presented in figure form. CONCLUSIONS: The computational examples demonstrate the importance of conducting post-hoc probes of moderational and mediational effects.

Adolescent↗