Calibration of (109)Cd KXRF systems for in vivo bone lead measurements: weighted least-squares regression with different weighting functions.

The use of iteratively reweighted least squares (IRLS) has recently been described as an alternative to ordinary least squares with heteroscedastic data, in the calibration of (109)Cd KXRF systems for in vivo bone lead measurements. This work addresses the use of weighted least squares (WLS) with two different weighting functions and no iteration, with that same data set. The functions are defined as the inverse of the variance of observed ratios of lead to coherent peak amplitudes and the inverse of the square of the error reported by the Marquardt fitting program for these ratios. The results show that if no iteration is implemented when using WLS, then the two weighting functions are highly inefficient in homogenizing the residual variance. Moreover, both methods estimate much more imprecise calibration intercepts and slopes than did the IRLS method. Work is in progress to investigate the implementation of IRLS with these weighting functions, with the focus on the selection of the best function for residuals to be used in each iteration stage.

Calibration of (109)Cd KXRF systems for in vivo bone lead measurements: the guiding role of the assumptions for least-squares regression in practical problem solving.

The use of least-squares regression to probe the level of lead contamination of plaster of Paris standards in the calibration of (109)Cd KXRF systems for bone lead measurement, as well as the use of iteratively reweighted least-squares (IRLS) in the case of violation of the assumptions for ordinary least-squares (OLS), is discussed here. One common violation is non-uniform residual variance, which makes the use of OLS inappropriate due to strong influence of points with large variance on the calibration line and variance of the slope and intercept. Comparison between OLS and IRLS in that case showed that IRLS estimates of the intercept are significantly smaller and more precise than OLS estimates, while a less marked increase in the calibration slope is observed when IRLS is used. Moreover, OLS underestimates bone lead concentrations at low levels of lead exposure and overestimates those concentrations at higher levels. These discrepancies are smaller in magnitude than the measurement uncertainty of conventional systems, except for high concentrations. For the newly developed cloverleaf systems, the suggested differences at bone lead concentrations below 17 ppm are comparable to the minimum detection limit, but are larger than the measurement uncertainty for bone lead concentrations above 60 ppm.

Oral theophylline for chronic obstructive pulmonary disease.

BACKGROUND: Oral theophylline has, for many years, been used as a bronchodilator in patients with COPD. Despite the introduction of new drugs, and its narrow therapeutic index, theophylline is still recommended for COPD treatment. OBJECTIVES: To determine the effectiveness of oral theophylline when compared to placebo in patients with stable COPD. SEARCH STRATEGY: The Cochrane Airways Review Group and Cochrane Controlled Clinical Registers were searched. SELECTION CRITERIA: All studies were randomised controlled trials (RCTs). DATA COLLECTION AND ANALYSIS: Data were independently abstracted and the methodological quality assessed by two reviewers. MAIN RESULTS: Twenty RCTs met the inclusion criteria. Concomitant therapy varied from none to any other bronchodilator plus corticosteroid (oral and inhaled). The following outcomes were significantly different when compared to placebo. FEV1 improved with treatment: Weighted Mean Difference (WMD) 100 ml; 95% Confidence Interval (95%CI) 40, 160 ml. Similarly for FVC: WMD 210 ml 95%CI 100, 320. Two studies reported an improvement in VO2max; WMD 195 ml/min, 95%CI 113,27). At rest, PaO2 and PaCO2 both improved with treatment (WMD 3.2 mmHg; 95%CI = 1.2, 5., and WMD -2.4 mmHg; 95%CI = -3.5, -1.2, respectively). Walking distance tests did not improve (4 studies, Standardised Mean Difference 0.30, 95%CI -0.01, 0.62), neither did Visual Analogue Score for breathlessness isn two small studies (WMD 3.6, 95%CI -4.6, 11.8). The Relative Risk (RR) of nausea was greater with theophylline (RR 7.7; 95%CI 1.5, 39.9). However, patients' preference for theophylline was greater than that for placebo (RR 2.27; 95%CI = 1.26, 4.11). Very few patient withdrew from these studies for any reason. REVIEWER'S CONCLUSIONS: Theophylline has a modest effect on FEV1 and FVC and slightly improves arterial blood gas tensions in moderate to severe COPD. These benefits were seen in patients receiving a variety of different concomitant therapies. Improvement in exercise performance depended on the method of testing. There was a very low dropout rate in the studies that could be included in this review, which suggests that recruited patients may have been known by the investigators to be theophylline tolerant. This may limit the generalisability of these studies.

Effects of Tropical Rotation Crops on Meloidogyne arenaria Population Densities and Vegetable Yields in Microplots.

The effects of 12 summer crop rotation treatments on population densities of Meloidogyne arenaria race 1 and on yields of subsequent spring vegetable crops were determined in microplots. The crop sequence was: (i) rotation crops during summer 1991 ; (ii) cover crop of rye (Secale cereale) during winter 1991-92; (iii) squash (Cucurbita pepo) during spring 1992; (iv) rotation crops during summer 1992; (v) rye during winter 1992-93; (vi) eggplant (Solanum melongena) during spring 1993. The 12 rotation treatments were castor (Ricinus communis), cotton (Gossypium hirsutum), velvetbean (Mucuna deeringiana), crotalaria (Crotalaria spectabilis), fallow, hairy indigo (Indigofera hirsuta), American jointvetch (Aeschynomene americana), sorghum-sudangrass (Sorghum bicolor x S. sudanense), soybean (Glycine max), horsebean (Canavalia ensiformis), sesame (Sesamum indicum), and peanut (Arachis hypogaea). Compared to peanut, the first eight rotation treatments resulted in lower (P

Tropical rotation crops influence nematode densities and vegetable yields.

The effects of eight summer rotation crops on nematode densities and yields of subsequent spring vegetable crops were determined in field studies conducted in north Florida from 1991 to 1993. The crop sequence was as follows: (i) rotation crops during summer 1991; (ii) cover crop of rye (Secale cereale) during winter 1991-92; (iii) 'Lemondrop L' squash (Cucurbita pepo) during spring 1992; (iv) rotation crops during summer 1992; (v) rye during winter 1992-93; (vi) 'Classic' eggplant (Solanum melongena) during spring 1993. The eight summer crop rotation treatments were as follows: 'Hale' castor (Ricinus communis), velvetbean (Mucuna deeringiana), sesame (Sesamum indicum), American jointvetch (Aeschynomene americana), weed fallow, 'SX- 17' sorghum-sudangrass (Sorghum bicolor x S. sudanense), 'Kirby' soybean (Glycine max), and 'Clemson Spineless' okra (Hibiscus esculentus) as a control. Rotations with castor, velvetbean, American jointvetch, and sorghum-sudangrass were most effective in maintaining the lowest population densities of Meloidogyne spp. (a mixture of M. incognita race 1 and M. arenaria race 1), but Paratrichodorus minor built up in the sorghum-sudangrass rotation. Yield of squash was lower (P