Test-retest reliability in EEG frequency analysis.

This study was performed to gain a better understanding of EEG frequency analysis test-retest reliability in normal healthy adults, and to evaluate factors which could influence the measured inter-record differences. Nineteen subjects underwent serial EEG recordings at 5 min and 12-16 week intervals. Records were visually edited using a standardized protocol, and FFT frequency analysis performed on segments of 60, 40, or 20 sec total length. Correlation coefficients for broad band features averaged 0.92 over the 5 min retest interval and 0.84 over the 12-16 week interval. There was essentially no difference between correlation coefficients of absolute and relative power features. Coefficients based on 60 sec records were marginally higher than those of 40 or 20 sec records. On the other hand, test-retest percent differences were typically lower for relative as opposed to absolute power features, and 60 sec records showed consistently lower percent differences than did 40 or particularly 20 sec records. Peak alpha frequency and mean frequency were the most stable EEG features at either interval. Montage had significant effects on test-retest differences at the 12-16 week interval. A significant association between intra-record and inter-record variability could not be demonstrated.     

Maternal weight gain, infant birth weight, and diet: causal sequences

The causal sequence maternal nutrition----maternal weight gain----infant birth weight is not sustained by available evidence except under extreme nutritional deprivation. For maternal weight change, diet effects of near starvation are unequivocal. With chronic undernutrition or social deprivation, diet effects are inapparent or modest (conditional on pregnancy stage, diet supplement, and prepregnancy weight). For birth-weight change, diet effects of near starvation are likewise unequivocal and modest with chronic undernutrition or social deprivation. The complete causal sequence has been demonstrated only below a famine threshold. Outside famine, effects are modest (conditional on baseline nutrition, timing, and content of diets, possibly also on infant sex and energy expenditure). High-protein concentrations have produced adverse effects. Micronutrients and consequent fluid retention could have favorable effects. Diet effects on birth weight apparently bypass maternal weight change. Hence, to enhance birth weight, maternal diet appears to deserve more attention than does weight gain.