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.      

The temporal pattern of recovery of myocardial perfusion and metabolism delineated by positron emission tomography after coronary thrombolysis

Recovery of mechanical function by ischemic myocardium is dependent on the restoration of nutritive blood flow and oxidative metabolism subsequent to reperfusion. To characterize the time course and extent of recovery of perfusion and metabolism, we used positron emission tomography with 15O-labeled water and 11C-labeled palmitate to sequentially study six dogs after 2 hr of ischemia followed by reperfusion for 4 wk. Myocardial blood flow in the ischemic region increased from 15 +/- 8% of normal during coronary occlusion to 82 +/- 25% 1 hr after reperfusion. Despite maintained coronary patency documented angiographically, flow was reduced after 24 hr to 37 +/- 16% of normal. This decrease was temporary, with flow returning to 66 +/- 11%, 62 +/- 7%, and 64 +/- 18% of normal after 1, 2, and 4 wk of reperfusion, respectively. Uptake of 11C-labeled palmitate paralleled alterations in perfusion during ischemia and early reperfusion, averaging 32 +/- 15% of normal during ischemia, and 67 +/- 22% and 36 +/- 10% after 1 and 24 hr of reperfusion. After that, palmitate uptake was more variable. Flow and fatty acid uptake after 4 wk of reperfusion were not related to collateral flow during ischemia or the extent of initial reperfusion. However, uptake of palmitate 1 hr after reperfusion was a strong predictor of the uptake of palmitate 4 wk after reperfusion (r = 0.86, p less than 0.03). The results indicate that positron emission tomography with 15O-labeled water and 11C-labeled palmitate may be useful for assessing the success of recanalization in restoring nutritive perfusion and fatty acid metabolism and that the uptake of [11C]palmitate early after reperfusion predicts the ultimate salvage of myocardium.     

Brain dysfunction in social drinkers

Thirty-four social drinkers who had referred themselves to the Regional Brain Damage Unit for assessment of the effects of drinking alcohol were compared with 42 volunteer control subjects of equivalent age but with low alcohol intake, using two 'learning' tests — the Rey Auditory Verbal Learning Test (RAVLT) and the Austin Button Maze. The Maze Test gave no evidence of disorder, but the two groups were significantly different on the RAVLT. No abnormalities in standard cognitive tests were apparent. These results suggest that a deficit in learning ability may be an early feature of the brain dysfunction associated with excessive alcohol consumption.     

Interventional dysrhythmia management and the role of laser

Drug-resistant dysrhythmias may require interventional management. Laser energy can be used for interruption or destruction of dysrhythmia-generating foci or conductive pathways. Lasers may, therefore, be useful tools for interventional management of supraventricular or ventricular dysrhythmias and preexcitation syndromes. Although the role of lasers in interventional dysrhythmia management is not clearly defined, the advantages may be substantial.     

Petit Mal-Grand Mal ECT: A Method to Induce Seizures Without Barbiturate Anesthesia

Petit mal-grand mal (PM-GM) electroconvulsive therapy (ECT) is a technique developed by Impastato to elicit unconsciousness with a subconvulsive electrical stimulus, rather than with barbiturate anesthesia. Muscle relaxation is produced with succinylcholine chloride before stimulus is applied. The cases reported here illustrate applications of the technique to depressed patients with severe cardiac and pulmonary disease, and the use of PM-GM ECT in a patient in whom seizures could not be elicited by the usual ECT technique is described.     

Impact of clinical history on fracture detection with radiography

The effect of knowledge of localizing symptoms and signs in the detection of fractures was studied. Forty radiographs of the extremities were examined twice by seven radiologists; the sessions were separated by 4 months. In 26 cases, a subtle fracture was present; 14 cases were normal. In half of the cases at each session, the precise location of pain, tenderness, or swelling was provided. The observer was asked to determine if the case was normal or abnormal (provide the exact location of the fracture) and to indicate the degree of confidence in the diagnosis. Responses were converted to a numeric scale for analysis. Analysis of receiver operator characteristic parameters indicates that clues regarding location of trauma facilitate detection of fractures. The improvement is based largely on an increased true-positive rate without an increased false-positive rate, regardless of the decision criteria of the radiologist (overall willingness to "overread" or "underread"). This has direct clinical applicability and reinforces the plea of radiologists for precise clinical information.