Median Absolute Percentage Difference Research Articles

Increased dominance of terrestrial component in dissolved organic matter in Chinese lakes

The source composition of chromophoric dissolved organic matter (CDOM) in lakes is closely related to regional environmental changes, human activities, and the carbon cycle. The spectral slope ratio (SR) is an important parameter of CDOM optical components, and combined with remote sensing technology, the source composition of CDOM can be tracked comprehensively and efficiently in large regions. Here, we proposed a CDOM source tracking remote sensing model (CDOM-SR) based on the hue angle (α) to assess the spatial pattern and long-term trend of the CDOM source composition in Chinese lakes (surface area ≥ 1 km2) from 1986 to 2021. Validation results show that the CDOM-SR model has a good SR estimation performance with a median absolute percentage difference, root mean square deviation, median ratio, and median deviation of 17.91 %, 0.23, 1.02, and 0.03, respectively. We found that the average SR of Chinese lakes presents an obvious spatial pattern of high in the west and low in the east due to the difference in human activity intensity and the natural geographical environment. Additionally, we found that the average SR of Chinese lakes from 1986 to 2021 decreased at a rate of - 0.06/10 years, of which 64.37 % of lakes decreased significantly, 15.42 % of lakes had no significant change, and only 20.20 % of lakes increased. The widespread decrease in the average SR indicates that the increasing human activity discharge of terrestrial organic matter has had an important impact on the source composition of the CDOM in Chinese lakes. Our results provide a new resource for remote sensing monitoring of CDOM sources and important insights into lake carbon cycling under the influence of ongoing human activities.

Resolving phytoplankton pigments from spectral images using convolutional neural networks

AbstractMotivated by the need for rapid and robust monitoring of phytoplankton in inland waters, this article introduces a protocol based on a mobile spectral imager for assessing phytoplankton pigments from water samples. The protocol includes (1) sample concentrating; (2) spectral imaging; and (3) convolutional neural networks (CNNs) to resolve concentrations of chlorophyll a (Chl a), carotenoids, and phycocyanin. The protocol was demonstrated with samples from 20 lakes across Scotland, with special emphasis on Loch Leven where blooms of cyanobacteria are frequent. In parallel, samples were prepared for reference observations of Chl a and carotenoids by high‐performance liquid chromatography and of phycocyanin by spectrophotometry. Robustness of the CNNs were investigated by excluding each lake from model trainings one at a time and using the excluded data as independent test data. For Loch Leven, median absolute percentage difference (MAPD) was 15% for Chl a and 36% for carotenoids. MAPD in estimated phycocyanin concentration was high (102%); however, the system was able to indicate the possibility of a cyanobacteria bloom. In the leave‐one‐out tests with the other lakes, MAPD was 26% for Chl a, 27% for carotenoids, and 75% for phycocyanin. The higher error for phycocyanin was likely due to variation in the data distribution and reference observations. It was concluded that this protocol could support phytoplankton monitoring by using Chl a and carotenoids as proxies for biomass. Greater focus on the distribution and volume of the training data would improve the phycocyanin estimates.

Widespread decrease in chromophoric dissolved organic matter in Chinese lakes derived from satellite observations

Chromophoric dissolved organic matter (CDOM) can significantly influence underwater light fields, nutrient availability, and microbial activity; thus, it plays an essential role in physical, chemical, and biological processes in aquatic ecosystems. China has undergone significant changes in climate, water quality improvement, and human processes over the past few decades. However, the impact of these processes on CDOM in Chinese lakes is unclear. Therefore, in this study, we aimed to reconstruct long-term and high-resolution CDOM data from Landsat satellite images using a simple model to characterise changes in CDOM in 2462 Chinese lakes (surface area ≥ 1 km2) from 1986 to 2021. Validation results demonstrated that the model performed adequately in deriving the CDOM absorption coefficient at 350 nm, with a root mean square deviation, median deviation, median absolute percentage difference, and median ratio of 0.68 m−1, 0.02 m−1, 19.76%, and 1.01, respectively. We observed a distinct spatial pattern of CDOM, with higher CDOM in eastern China with intensive human activities but lower CDOM in western China with strong ultraviolet radiation. Temporally, mean aCDOM(350) of Chinese lakes from 1986 to 2021 decreased at a rate of - 0.25 m−1/10 years. We also revealed that increased regional vegetation coverage and improved water quality mainly drive CDOM decline in lakes on the Qinghai Tibet Plateau Region and Eastern Plain Region, respectively. The widespread decrease in CDOM, in turn, has contributed to changes in the optical properties and biogeochemical cycles of Chinese lakes. Our results provide valuable insights for lake environmental protection and water quality management in China.

Estimation of vertical size-fractionated phytoplankton primary production in the northern South China Sea

Modelling vertical changes of size-fractionated phytoplankton primary production (PP) offers a holistic route to describe marine ecosystems and constitutes an important part of remote sensing to accurately estimate the depth-integrated PP in the global oceans. However, there is no size-fractionated PP model established in the Northern South China Sea (NSCS) yet. In situ measured hyperspectral absorption and irradiance data were used to estimate vertical size-fractionated PP. Results demonstrated that the estimated size-fractionated PP showed good agreement with in-situ measurement. r2s are 0.41, 0.69, and 0.83, and median absolute percentage difference are 23.33%, 25.86%, and 31.05% for pico-, nano-, and micro-PP, respectively. The intercept from the linear relationship between ratio of phytoplankton absorption coefficient (aph(4 3 5)/aph(6 7 6)) and quantum yield of photosynthesis have the biggest impact on estimation of PP based on Monte Carlo approach. The model derived PP profiles showed an exponential attenuation shape curve from the surface to the bottom in coastal water of NSCS. In contrast, a decreasing pattern with increasing depth with a maximum in the subsurface layer or at the chlorophyll maximum depth was observed in the open ocean of NSCS. Such an approach can be utilized to depict the vertical variations of size-fractionated PP, which can serve as supplementary of remote sense to reveal their three-dimensional structure.

Estimating the water-leaving albedo from ocean color

Water-leaving albedo (αw), defined as the ratio of water-leaving irradiance to downwelling irradiance just above the surface, is a major component of ocean surface albedo (α) but has long been ignored or underrepresented. A semi-analytical scheme based on inherent optical properties (IOPs), termed IOPs-αw, is proposed in this study to estimate spectral αw(λ) from ocean color measurements. Evaluations with numerical simulations of radiative transfer show that IOPs-αw outperforms the conventional scheme based on chlorophyll-a (Chl) concentration. The median absolute percentage difference (MAPD) of derived αw(λ) from IOPs-αw is generally less than 3% in the blue-green spectral domain, in comparison to MAPD of over 40% for estimated αw(λ) from the Chl-based scheme. IOPs-αw is later implemented to monthly composite data of the Visible Infrared Imaging Radiometer Suite (VIIRS), where reasonable spatial distributions and seasonal patterns of αw(λ) are obtained. In particular, broadband αw in the visible domain, termed αw_VIS, obtained via IOPs-αw is over 50% higher than the previous estimation by the Chl-based scheme in most oceanic waters. Furthermore, this study concludes that αw_VIS could contribute up to 20% to α in oceanic waters under low solar-zenith angles. Thus, we suggest that neither the spatial variability of αw_VIS nor the contribution of αw_VIS to α shall be neglected, and it is necessary to incorporate IOPs-αw into current parameterizations of α in coupled ocean-atmosphere and climate models.

Global Estimation of Suspended Particulate Matter From Satellite Ocean Color Imagery.

The suspended particulate matter (SPM) concentration (unit: mg l−1) in surface waters is an essential measure of water quality and clarity. Satellite remote sensing provides a powerful tool to derive the SPM with synoptic and repeat coverage. In this study, we developed a new global SPM algorithm utilizing the remote sensing reflectance (R rs (λ)) at near‐infrared (NIR), red, green, and blue bands (NIR‐RGB) as input. The evaluations showed that the NIR‐RGB algorithm could predict SPM with the median absolute percentage difference of ∼35%–39% over a wide range from ∼0.01 to >2,000 mg l−1. The uncertainty is smaller (29%–37%) for turbid waters where R rs (671) ≥ 0.0012 sr−1 and slightly higher (41%–44%) for clear waters where R rs (671) < 0.0012 mg l−1. The algorithm was implemented with the global R rs (λ) data from the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar‐orbiting Partnership (SNPP) satellite. We provided a brief characterization of the spatial distribution and temporal trends of the SPM products in global waters based on the monthly SPM composites. Case studies of the SPM time series in coastal and inland waters suggest that the satellite SPM estimations registered spatial and seasonal variation and episodic events in regional scales as well. The VIIRS‐generated global SPM maps provide a valuable addition to the existing ocean color products for environmental and climate applications.

Thermodilution Cardiac Index Has Poor Agreement with That Measured by the Direct Fick Method in Low-Output States

<h3>Purpose</h3> The thermodilution (Td) method is routinely used for measurement of cardiac output although its accuracy in low-output states remains uncertain. Criteria for designating heart transplant listing status in the contemporary allocation system is incumbent on meeting strict cardiac index (CI) cutoffs. We aimed to assess the agreement between Td and direct Fick (dFick) CI in patients with low CI. <h3>Methods</h3> In this retrospective analysis of 535 patients who underwent right heart catheterization with dFick CI measurement as part of clinically indicated hemodynamic evaluation using the gold-standard Douglas bag technique, 253 patients had both Td/dFick CI measurements. Three saline injections were typically used and averaged in Td CI measurements. We included 118 patients who specifically had a CI of </= 2.2 L/min/m² by dFick method. Agreement between Td and dFick method was assessed by median absolute percentage difference, Spearman's rank correlation, and Bland-Altman Method. <h3>Results</h3> Among the 118 patients included (Mean [SD] age 60 [12.2] years, 42.3% female), Median (interquartile range, IQR) overall dFick and Td CI values differed significantly (1.86 [1.65, 2.1] and 2.03 [1.78, 2.31] L/min/m², respectively; P<0.001). The two measurements weakly correlated (r_s=0.31, P<0.001), with a systematic error introduced by Td CI expressed a mean difference of 0.21 (-0.61, 1.03) L/min/m² (Figure). Median (IQR) absolute percentage difference between Td and dFick was 16.9 (7.9, 27.9)%. Td and dFick CI's differed by >25% in 33.1% of patients. <h3>Conclusion</h3> The agreement of Td with the gold-standard dFick CI measurements in patients with low CI was suboptimal. These data are important consider in in clinical scenarios such as heart transplant listing status where strict hemodynamic cutoffs guide urgency.

285 Accuracy of estimated fetal weight in extremely preterm infants and the impact of obesity

Obesity is increasingly common among reproductive age women, placing them at increased risk for obstetrical complications including preterm birth. Our objective was to determine the accuracy of ultrasound derived estimated fetal weight (EFW) in preterm infants born less than 32 weeks and determine if accuracy varied by prepregnancy body mass index (BMI). We also sought to evaluate the accuracy of EFW among small for gestational age (SGA) versus appropriately grown (AGA) preterm infants. We included women who delivered between 230/7 and 316/7 weeks’ gestation who had an ultrasound EFW within 7 days of delivery. We excluded women with missing prepregnancy BMI data (n=13). Mean percentage difference and median absolute percentage difference between EFW and BW were calculated using the formula (EFW-BW)/BWx100%. We then used Anova or t-test to compare the accuracy of EFW between groups. A total of 641 women were included in our cohort with a mean gestational age of 28.3 ± 2.6 weeks and mean birthweight of 1110.3 ± 425.3g. Among women in the cohort, a total of 3.6% were underweight, 37.3% were of normal weight, 23.7% were overweight, and 35.4% were obese. The mean percentage difference between EFW and BW was 7.7 ± 11.2% among all infants. As can be seen in Fig 1, EFW is skewed toward overestimating BW. The median absolute percentage difference between EFW and BW was 9.2% (IQR: 4.3-15.2). The mean accuracy of EFW varied by BMI category (Fig 2) with a mean accuracy of 6.7 ± 11.3% in normal weight women and 9.5 ± 11.5 % in obese women (p=0.02). Among SGA infants (n=125), the mean percentage difference between EFW and BW was 12.6 ± 10.4%, versus 6.5 ± 11.0% among AGA infants (p<0.001). While ultrasound EFW overestimates birthweight in this cohort, most estimates were within 10% of actual birthweight. The accuracy of EFW was worse in obese women compared to normal weight women. Ultrasound EFW also significantly overestimated BW in SGA infants. This is important when counseling women facing preterm delivery, especially those who are predicted to be small for gestational age.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Accuracy of estimated fetal weight assessment in fetuses with congenital diaphragmatic hernia

Congenital diaphragmatic hernia is a congenital anomaly in which fetal abdominal organs herniate into the thoracic cavity through a diaphragmatic defect, which can impede fetal lung development. Standard formulas for estimated fetal weight include measurement of fetal abdominal circumference, which may be inaccurate in fetuses with congenital diaphragmatic hernia because of displacement of abdominal contents into the thorax. This study aimed to assess the accuracy of standard estimated fetal weight assessment in fetuses with congenital diaphragmatic hernia by comparing prenatal assessment of fetal weight with actual birthweight. A retrospective cohort study of fetuses diagnosed with congenital diaphragmatic hernia was performed at a single center from 2012 to 2018. Fetuses with multiple anomalies or confirmed chromosome abnormalities were excluded. Estimated fetal weight was calculated using the Hadlock formula. Published estimates of fetal growth rate were used to establish a projected estimated fetal weight at birth from the final growth ultrasound, and the percentage difference between projected estimated fetal weight at birth and actual birthweight was calculated. A Wilcoxan rank-sum test was used to examine the difference between projected estimated fetal weight and birthweight. We had complete data for 77 fetuses with congenital diaphragmatic hernia. The majority (76.6%, 55 of 77) had left-sided congenital diaphragmatic hernia. The median [interquartile range] projected estimated fetal weight was similar to median birthweight, at 3177 g [2691-3568] and 3180 g [2630-3500], respectively, which did not represent a statistically significant difference between projected estimated fetal weight and birthweight (P= .66). The median absolute percentage difference between projected birthweight and actual birthweight was 6.3% [3.2-7.0]. Estimated fetal weight was overall underestimated in a minority of cases (44.2%, 34 of 77). In fetuses with a congenital diaphragmatic hernia,standard measurements of fetal estimated fetal weight show accuracy that is at least comparable with previously established margins of error for ultrasound assessment of fetal weight. Standard estimated fetal weight assessment remains an appropriate method ofestimating fetal weight in fetuses with congenital diaphragmatic hernia.

Retrieval Algorithm of Chlorophyll-a Concentration in Turbid Waters from Satellite HY-1C Coastal Zone Imager Data

Chen, X.-Y.; Zhang, J.; Tong, C.; Liu, R.-J.; Mu, B., and Ding, J., 2019. Retrieval algorithm of chlorophyll-a concentration in turbid waters from satellite HY-1C coastal zone imager data. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 146-155. Coconut Creek (Florida), ISSN 0749-0208.The satellite HY-1C was successfully launched in September 2018 with the Coastal Zone Imager (CZI) onboard, which can provide optical images of 50-m resolution at four broad bands (blue, green, red and near-infrared). In this study, 305 sets of in-situ measurements collected between 2005 and 2015 in the Bohai, Yellow and East China seas were used to assess the performance of HY-1C in retrieving chlorophyll-a concentration in the coastal waters. The results showed that two algorithms based on blue-green band ratios (OC3 and OC3L) performed well. The median of the ratio of retrieved to in-situ values was about 1.1, and the median absolute percentage difference was about 40 %. After applying the two algorithms to HY-1C CZI data of Jiaozhou Bay (Qingdao, China), the spatial distribution of retrieved Chl-a data was found to be in good agreement with results based on data from another satellite (Landsat-8 OLI) with a median absolute percentage difference less than 15 %. The results showed that the broadband channels of the HY-1C CZI can retrieve Chl-a concentration in turbid waters, which indicates potential for its application in coastal water quality and eutrophication monitoring.

Semianalytical Derivation of Phytoplankton, CDOM, and Detritus Absorption Coefficients From the Landsat 8/OLI Reflectance in Coastal Waters

AbstractThe Operational Land Imager (OLI) onboard Landsat 8 has potential for mapping the water bio‐optical properties with high spatial resolution. Landsat 8/OLI generates the remote sensing reflectance (Rrs) at four visible bands (λ1‐4 = 443, 482, 561, and 655 nm) and is lack of a 412‐nm band commonly included for ocean color sensors. This spectral configuration has limited the use of Landsat 8/OLI reflectance product for analytical derivation of light absorption coefficients of phytoplankton, colored dissolved organic matter (CDOM), and detritus. In this study, we proposed a hybrid approach to fill this gap. First, we developed an algorithm to estimate the reflectance in a virtual band centered at λ0 = 412 nm from the OLI reflectance spectra Rrs(λ1‐4). Both the estimated Rrs(λ0) and measured Rrs(λ1‐4) were then used together to retrieve the water component absorption coefficients with existing algorithms including the quasi‐analytical algorithm. We assessed the model performance using in situ measurements from the global waters. It was found that the proposed approach could estimate Rrs(412) with a median absolute percentage difference of ~9%. The subsequent retrievals of the component absorption coefficients were satisfactorily accurate, with median absolute percentage difference roughly equal to 35%, 40%, and 60% for phytoplankton, CDOM, and detritus, respectively. The results suggest the feasibility to generate analytically the component absorption coefficients from the Landsat 8/OLI reflectance.

Evaluation of standard and regional satellite chlorophyll-a algorithms for moderate-resolution imaging spectroradiometer (MODIS) in the Bohai and Yellow Seas, China: a comparison of chlorophyll-a magnitude and seasonality

ABSTRACTRetrieval of satellite remotely sensed chlorophyll-a (chl-a) concentrations in coastal regions such as the Bohai and Yellow Seas (BYS) is challenging due to their complex oceanic and atmospheric optical properties. The standard OC3M (ocean chl-a three-band algorithm for MODIS (moderate-resolution imaging spectroradiometer)) algorithm has been widely used in the BYS, despite well-known uncertainties about its accuracy in terms of absolute magnitude. This was based on the belief that OC3M chl-a is capable of representing reliable relative spatial and temporal patterns of sea surface chl-a concentrations. In this study, the ability of the standard OC3M chl-a algorithm to reproduce accurate seasonality patterns was evaluated, based on comparisons with in situ chl-a measurements in the BYS. The results quantified the overestimation by the standard OC3M algorithm with a median absolute percentage difference of 98.48% and a median relative difference of 1.13 mg m−3.More importantly, the seasonality from OC3M chl-a was significantly biased relative to the seasonal patterns of in situ chl-a. In addition, a regional GAM (generalized additive model)-based satellite chl-a algorithm was evaluated and compared with OC3M chl-a. The results showed the GAM chl-a improved accuracy in both magnitude and seasonality when compared with in situ chl-a, relative to that from OC3M chl-a.

Accuracy of Ultrasound Estimated Fetal Weight in Small for Gestational Age and Appropriate for Gestational Age Grown Periviable Neonates.

Clinicians use estimated fetal weight (EFW) as a proxy for birth weight (BW) in the antenatal period. Our objective was to compare the accuracy of EFW obtained by ultrasound to BW among infants born during the periviable period and determine if accuracy of EFW varied among small for gestational age (SGA) versus appropriate for gestational age (AGA) grown neonates. We included women who delivered between 230/7 and 256/7 weeks' gestation and had an EFW within 7 days of delivery. Mean percentage difference and median absolute percentage difference between EFW and BW were calculated. Our cohort included 226 neonates with a mean gestational age of 241/7 ± 0.8 weeks and median BW of 653 g (interquartile range [IQR]: 580-750 g). The median absolute percentage difference between EFW and BW of fetal weight estimates was 9.2% (IQR: 3.6-17.2). EFW overestimated BW for 75% (n = 171) of the cohort. Among SGA infants, the mean percentage difference in EFW and BW was 16.2 ± 19.4% versus 6.9% ± 13.1% in AGA infants (p = 0.019). EFW overestimated BW in this cohort. In addition, ultrasound was less accurate among infants born SGA. These data are important to consider when counseling families facing periviable delivery.

National scale evaluation of the InVEST nutrient retention model in the United Kingdom

A wide variety of tools aim to support decision making by modelling, mapping and quantifying ecosystem services. If decisions are to be properly informed, the accuracy and potential limitations of these tools must be well understood. However, dedicated studies evaluating ecosystem service models against empirical data are rare, especially over large areas. In this paper, we report on the national-scale assessment of a new ecosystem service model for nutrient delivery and retention, the InVEST Nutrient Delivery Ratio model. For 36 river catchments across the UK, we modelled total catchment export of phosphorus (P) and/or nitrogen (N) and compared model outputs to measurements derived from empirical water chemistry data.The model performed well in terms of relative magnitude of nutrient export among catchments (best Spearman's rank correlation for N and P, respectively: 0.81 and 0.88). However, there was wide variation among catchments in the accuracy of the model, and absolute values of nutrient exports frequently showed high percentage differences between modelled and empirically-derived exports (best median absolute percentage difference for N and P, respectively: ±64%, ±44%). The model also showed a high degree of sensitivity to nutrient loads and hydrologic routing input parameters and these sensitivities varied among catchments.These results suggest that the InVEST model can provide valuable information on nutrient fluxes to decision makers, especially in terms of relative differences among catchments. However, caution is needed if using the absolute modelled values for decision-making. Our study also suggests particular attention should be paid to researching input nutrient loadings and retentions, and the selection of appropriate input data resolutions and threshold flow accumulation values. Our results also highlight how availability of empirical data can improve model calibration and performance assessment and reinforce the need to include such data in ecosystem service modelling studies.

Echocardiographic estimation of mean pulmonary artery pressure in critically ill patients.

BackgroundIndirect assessment of mean pulmonary arterial pressure (MPAP) may assist management of critically ill patients with pulmonary hypertension and right heart dysfunction. MPAP can be estimated as the sum of echocardiographically derived mean right ventricular to right atrial systolic pressure gradient and right atrial pressure; however, this has not been validated in critically ill patients.MethodsThis prospective validation study was conducted in patients undergoing pulmonary artery catheterisation during intensive care admission. Pulmonary artery catheter (PAC) measurements of MPAP were contemporaneously compared to MPAP estimated utilising transthoracic echocardiography (TTE)-derived mean right ventricular to right atrial systolic pressure gradient added to invasively measured right atrial pressure.ResultsOf 53 patients assessed, 23 had estimable MPAP using TTE. The mean difference between TTE- and PAC-derived MPAP was 1.9 mmHg (SD 5.0), with upper and lower limits of agreement of 11.6 and −7.9 mmHg, respectively. The median absolute percentage difference between TTE- and PAC-derived MPAP was 7.5%. Inter-rater reliability assessment was performed for 15 patients, giving an intra-class correlation coefficient of 0.96 (95% confidence intervals, 0.89 to 0.99).ConclusionsThis echocardiographic method of estimating MPAP in critically ill patients was not equivalent to invasively measured MPAP, based on our predefined clinically acceptable range (±5 mmHg). The accuracy of this method in critically ill patients was similar to the results obtained in ambulatory patients and compared favourably with regard to the accuracy with echocardiographic estimation of systolic pulmonary arterial pressure. The utility of this technique is limited by frequent inability to obtain an adequate tricuspid regurgitant time-velocity integral in critically ill patients.

Revised equations for estimating glomerular filtration rate based on the Lund-Malmö Study cohort

Objective. To increase the accuracy of estimated GFR (eGFR) from creatinine overall and at measured GFR ≥90 mL/min per 1.73 m2 by revising the Lund-Malmö (LM) equations, to elaborate on more complex forms to improve the LM and CKD-EPI equations further, and to assess benefits of adding lean body mass (LBM). Material and methods. Swedish Caucasians (n = 850, 376 women; median 60, range 18–95 years) referred for GFR measurement (plasma iohexol-clearance: median 55, range 5–173 mL/min/1.73 m2) constituted the Lund-Malmö Study cohort. Bias, precision, accuracy, expressed as median absolute percentage difference and percentage of estimates ±10% (P10) and ±30% (P30) of measured GFR, and classification ability with respect to five GFR stages were compared with the original LM, CKD-EPI and MDRD equations. Results. LM Revised overall performed better than LM Original without LBM due to increased accuracy at measured GFR ≥90 mL/min/1.73 m2. Further extensions of the CKD-EPI or LM equations did not substantially improve overall performance. In particular, the performance of LM Revised at measured GFR ≥90 mL/min/1.73 m2 could not be improved further without decreasing accuracy and classification ability at lower GFR-levels. Adding LBM to the equations had no strong effect on accuracy. Conclusion. Comparisons with the CKD-EPI and MDRD equations suggest that the LM equations are superior for the present Swedish population, due to markedly higher accuracy of the LM equations at measured GFR <30 mL/min/1.73 m2. However, the LM equations cannot be recommended for use in general clinical practice until validated in other populations.

An Alternative Echocardiographic Method to Estimate Mean Pulmonary Artery Pressure: Diagnostic and Clinical Implications

The aim of this study was to evaluated an alternative echocardiographic method to calculate mean pulmonary arterial pressure (MPAP). One hundred two patients were studied with simultaneous right-heart catheterization (RHC) and echocardiography. MPAP was calculated by adding the right ventricular-right atrial mean systolic gradient to right atrial pressure. The mean difference between MPAP calculated using this method and RHC-derived MPAP was -1.6 mm Hg, less than that of traditional systolic pulmonary arterial pressure (SPAP; -6.4 mm Hg) and MPAP estimated using the pulmonary regurgitation method (-13.9 mm Hg). The median absolute percentage difference of the MPAP calculations relative to RHC was significantly less with this method than with the pulmonary regurgitation method (18% vs 71%; P < .001) and similar to the SPAP method (both 18%; P = .30). MPAP calculated using the proposed method is as accurate as SPAP calculation and less variable than previous methods, thus allowing widespread clinical use.

Biases in Retrospective Self-Reports of Time Use: An Empirical Study of Computer Users

Research on information systems (IS) use has often relied upon retrospective self-reports. One example is when the amount of time spent using a system is reported, often as an indication of user acceptance. In this study, self-assessments of computer usage are compared with computer-monitored interactive use and connect time for 401 managers and professionals. When self-assessed use was compared with logged interactive use, there was a 32% difference in the average amount of use (3.9 vs. 2.7 hours/day). When the self-assessment was compared with total connect time, the averages were similar to each other (3.9 vs. 4.0 hours). In both comparisons, though, there were considerable differences between individual self-assessments and logged time (with a median absolute percentage difference of 47% when compared with logged connect time). Individual estimates of use tended to regress toward the population's mean use. Those whose use of the system was relatively light overestimated their use, while heavy users underestimated theirs. When a test of the relationship between user satisfaction and amount of use was conducted using self-assessments, the relationship was not statistically significant. When the same test was conducted using logged connect time, the relationship was significant. These results suggest that care should be exercised in operationalizing the user acceptance construct through self-reports of time use.