Two new reliability indices, ordinal coefficient alpha and ordinal coefficient theta, are introduced. A simulation study was conducted in order to compare the new ordinal reliability estimates to each other and to coefficient alpha with Likert data. Results indicate that ordinal coefficients alpha and theta are consistently suitable estimates of the theoretical reliability, regardless of the magnitude of the theoretical reliability, the number of scale points, and the skewness of the scale point distributions. In contrast, coefficient alpha is in general a negatively biased estimate of reliability. The use of ordinal coefficients alpha and theta as alternatives to coefficient alpha when estimating the reliability based on Likert response items are recommended. The choice between the two ordinal coefficients depends on whether one is assuming a factor analysis model (ordinal coefficient alpha) or a principal components analysis model (ordinal coefficient theta).

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Background It is well established that alcohol consumption is associated with an increased risk of injury. This systematic review and meta-analysis addresses important methodological issues commonly encountered in the alcohol and injury field by delineating the effect of study design and alcohol consumption recall period on effects size magnitude and by conducting gender-specific analyses. Methods Meta-analyses using random effect models. Data sources were peer-reviewed studies on alcohol and injury from 1970 to 2009 from MEDLINE, Psych Info and on-line journals. Case-control or case crossover ED studies reporting injury risk and alcohol consumed six hours before injury were included. Results The overall odds of injury were 2.799 (2.214–3.538, p<0.001). For case-crossover studies, the odds were 3.815 (2.646–5.499, p<0.001), for ED case-control studies the odds were 1.977 (1.385–2.821, p<0.001) and for population case-control designs the odds were 3.145 (1.583–6.247, p<0.005). The ‘usual frequency’ recall period yielded an odds ratio of 4.235 (2.541–7.057, p<0.001), compared to 2.320 (1.789–3.008, p<0.001) for all other methods. There were significant differences in odds ratio magnitude when comparing studies by design and recall period. Females had higher odds of injury than males, 2.285 (1.361–3.836, p<0.005) vs. 1.071 (0.715–1.605, p=0.737). Conclusions Study design and alcohol consumption recall period have significant effects on effect size magnitude in estimating risk of injury from alcohol consumption six hours prior to injury. For the ‘usual frequency’ case-crossover design, significant moderator effects were found, resulting in over-estimates of injury risk from alcohol. ED case-crossover designs tend to overestimate risk and ED case-control designs tend to under-estimate. We provide recommendations for future ED research.

Background While alcohol consumption has been linked to breast cancer in women, few studies have controlled for possible biases created by including former or occasional drinkers in the abstainer reference group. We explored the potential for such misclassification errors as sources of bias in estimates of the alcohol-breast cancer relationship. Methods Meta-analyses of population case-control, hospital case-control, and cohort studies to examine relationships between level of alcohol use and breast cancer morbidity and/or mortality in groups of studies with and without different misclassification errors. Results Of 60 studies identified, only 6 were free of all misclassification errors. The abstainer reference group was biased by the inclusion of former drinkers in 49 studies, occasional drinkers (<10g ethanol per week) in 22 and by both these groups in 18. Occasional drinkers were also mixed with light or hazardous level drinkers in 21 studies. Unbiased estimates of the OR for breast cancer were 1.011 (95% CI: 0.891-1.148) among former drinkers (n = 11) and 1.034 (95% CI: 1.003-1.064) among occasional drinkers (n=17). Hazardous level drinking (>20g<41g ethanol/day) was not significantly associated with breast cancer in studies with occasional drinker bias. However, in studies free from occasional drinker bias, the OR for breast cancer was 1.085 (95% CI: 1.015-1.160) for low level (<21g/day) drinkers (n=17), 1.374 (95% CI: 1.319-1.431) for hazardous level drinkers (n=26) and 1.336 (95% CI: 1.228-1.454) for harmful level (>40g/day) drinkers (n=9). Conclusions While the great majority of studies of the alcohol-breast cancer link include misclassification errors, only misclassification of occasional drinkers was found to bias risk estimates significantly. Estimates based on error free studies confirmed that low, hazardous and harmful levels of alcohol use each significantly increase the risk of breast cancer.

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