Meta-analysis may be used to estimate an overall effect across a number of similar studies. A number of statistical techniques are currently used to combine individual study results. The simplest of these is based on a fixed effects model, which assumes the true effect is the same for all studies. A random effects model, however, allows the true effect to vary across studies, with the mean true effect the parameter of interest. We consider three methods currently used for estimation within the framework of a random effects model, and illustrate them by applying each method to a collection of six studies on the effect of aspirin after myocardial infarction. These methods are compared using estimated coverage probabilities of confidence intervals for the overall effect. The techniques considered all generally have coverages below the nominal level, and in particular it is shown that the commonly used DerSimonian and Laird method does not adequately reflect the error associated with parameter estimation, especially when the number of studies is small.

Muscle wasting occurs rapidly in the ICU setting. Ultrasonography is a useful surrogate measure for identifying future impairment. Vastus intermedius may be an important muscle to monitor in the future because it demonstrated the greatest change in muscle quality and had the strongest relationship to volitional measures.

Objective To test the effectiveness of, and explore interactions between, three interventions to prevent falls among older people. Design A randomised controlled trial with a full factorial design. Setting Urban community in Melbourne, Australia. Participants 1090 aged 70 years and over and living at home. Most were Australian born and rated their health as good to excellent; just over half lived alone. Interventions Three interventions (group based exercise, home hazard management, and vision improvement) delivered to eight groups defined by the presence or absence of each intervention. Main outcome measure Time to first fall ascertained by an 18 month falls calendar and analysed with survival analysis techniques. Changes to targeted risk factors were assessed by using measures of quadriceps strength, balance, vision, and number of hazards in the home. Results The rate ratio for exercise was 0.82 (95% confidence interval 0.70 to 0.97, P=0.02), and a significant effect (P < 0.05) was observed for the combinations of interventions that involved exercise. Balance measures improved significantly among the exercise group. Neither home hazard management nor treatment of poor vision showed a significant effect. The strongest effect was observed for all three interventions combined (rate ratio 0.67 (0.51 to 0.88, P=0.004)), producing an estimated 14.0% reduction in the annual fall rate. The number of people needed to be treated to prevent one fall a year ranged from 32 for home hazard management to 7 for all three interventions combined. Conclusions Group based exercise was the most potent single intervention tested, and the reduction in falls among this group seems to have been associated with improved balance. Falls were further reduced by the addition of home hazard management or reduced vision management, or both of these. Cost effectiveness is yet to be examined. These findings are most applicable to Australian born adults aged 70-84 years living at home who rate their health as good.

This study examined used, discarded rotary nickel-titanium instruments obtained from 14 endodontists in four countries, and identified factors that may influence defects produced during clinical use. A total of 7,159 instruments were examined for the presence of defects. Unwinding occurred in 12% of instruments and fractures in 5% (1.5% torsional, 3.5% flexural). The defect rates varied significantly among endodontists. Instrument design factors also influenced defect rate, but to a lesser extent. The mean number of uses of instruments with and without defects was 3.3 +/- 1.8 (range: 1-10), and 4.5 +/- 2.0 (range: 1-16), respectively. The most important influence on defect rates was the operator, which may be related to clinical skill or a conscious decision to use instruments a specified number of times or until defects were evident.