Over- and underestimations

Figure 27 Errors in electron affinities (as compared to experiment) for self-consistent B3LYP/aug-cc-pVTZ calculations, and also for cases where the B3LYP energies for the neutral molecule and the anion were evaluated using Hartree-Fock densities (HF-B3LYP). The dashed horizontal lines are mean errors, which include considerable cancellation between over- and underestimation of the experimental EAs. The data set is except that the CN molecule is removed because of spin contamination in the Hartree-Fock determinant. Adapted with permission from Ref. 313 copyright 2011 American Institute of Physics.

In radiation protection and risk assessment linear extrapolations are commonly used. Linearity, however, is not based on experimental evidence in the very low dose range and a departure from it would imply an over- or underestimation of risks. There are both theoretical and experimental indications wich contradict the linearity at doses considered here (e.g. Brown, 1977 ... 

If the objective of measuring FMs, or other consumer product chemicals for that matter, in wastewater treatment is to understand FM removal and mechanisms of removal across wastewater treatment processes, then it is important to collect samples at least every 2 h and composite these samples into a single, flow-based 24-h sample. Otherwise, the results may be significantly over- or underestimated depending on the time of the day the sample was collected. However, if the objective is to monitor FMs in only final effluent or sludge, representative grab sampling may be sufficient. 

The Amb a 1 concentration of the final purified intermediate bulk is determined by an absorbance method chosen for its precision, accuracy, and simplicity. Because Amb a 1 bulk intermediate will now be conjugated to 1018 ISS (and the number of linked 1018 ISS affects the activity of the resulting AIC), it is essential to quantitate the Amb a 1 concentration accurately and precisely. A significant over- or underestimation of protein concentration will result in an over- or underestimation of the heterobifunctional linker required to activate the protein for coupling to 1018 ISS. The absorbance method, more dependent on well-calibrated instrumentation than lab technique, was chosen because it is an easy procedure to transfer to the production site. Dilution skills are the only requirement for robust performance of a well-developed and validated absorbance method. Hence a contract manufacturing site could readily quantitate Amb a 1 without the... 

Bias Occurs when there is a tendency to produce results that differ in a systematic manner from the true values. A study with small systematic bias is said to have high accuracy. Bias may lead to over- or underestimation of the strength of an association. The sources of bias in epidemiology are many and over 30 specific types of bias have been identified. The main biases are selection bias, information bias, and bias due to confounding. 

For example, finished-product release specifications such as content uniformity are rarely correlated to clinical evidence rather, they are set according to compendial test standards. Furthermore, the functional relationship between in-process material characteristics and finished-product quality is seldom known at a high level hence, the assigned in-process specifications for some operations may over- or underestimate the true level of process capability. As the level of process understanding in the pharmaceutical industry increases, development of science- and evidence-based in-process and release specifications will improve the reliability of Cpk as a tool for process characterization. 

Figure 3 compares the results obtained for the Matisse bronze samples with LA-ICP-MS and ICP-MS for six elements zinc, tin, lead, arsenic, bismuth and silver. The best correlations between ICP-MS and LA-ICP-MS occur for silver, arsenic and tin. For zinc, lead and bismuth, the results by ICP-MS and LA-ICP-MS concur quite well for some samples. For the other samples, the values are either over or underestimated. Immiscibility of lead in copper, even at low concentrations, could explain the non-agreement for some samples between the ICP-MS and the LA-ICP-MS results (13). However, zinc and bismuth are miscible in copper at the concentrations encountered in the Matisse bronze sculptures. 

Crosstalk An unwanted contribution to a LC-MS/MS transition from a previous LC-MS/MS transition. The potential for crosstalk is higher when multiple analytes with identical product ion mass-to-charge ratios are being monitored and when sufficient time is not provided for emptying the collision cell between MRM or SRM transitions. Crosstalk leads to over- or underestimation of an analyte of interest (Tong et al., 1999). 

HF/3-21G 1 bond angles are not consistently over- or underestimated. Dihedrals do not seem to be consistently over-or underestimated by any of the three levels. The HF/3-21G 1 level breaks down completely for HOOH, where a dihedral angle of 180°, far from the experimental 119.1°, is calculated omitting this error of 61° and the ClCH2CH2OH HOCC dihedral error of 7.6° lowers the HF/3-210 error from 8.8 to 2.5°. The experimental value of 58.4° for the ClCH2CH2OH HOCC dihedral is suspect because of its anomalously large... 

C-X (X=0, N, F, Cl, S) bond lengths appear to be consistently neither over- nor underestimated by AMI, while PM3 tends to underestimate them as stated above, the PM3 lengths seem to be the more accurate (mean errors 0.013 versus 0.028 A for AMI). Both AMI and PM3 give quite good bond angles (largest error ca. 4°, except for HOF for which the AMI error is 7.1°). 

The yields of SO2 and DMS02 were, on a molar basis, 60 10% and approximatly 30%, respectively. Because of a series of difficulties in calibration, wall loss, and aerosol formation it is not possible to indicate whether the observed yield of DMSO is being over- or underestimated. As stated above the observed products snow that both abstraction and addition reaction pathways are operative,... 

The rate constant obtained for G + DMSO in air is slightly more than a factor of 2 slower than the value of (2.0 0.3) xlO 10 cm3 s 1 for the reactiom G + DMS (this laboratory, unpublished results). No effect of the O2 concentration was observed for the reaction of G with DMS. However, this rate constant is already close to the collision frequency and a small O2 effect could remain undetected within the precision of the present experimental method. In air the reaction of G with DMSO leads to the formation of SO , DMSO-), CO, HCHO, and HOOOH with yields of approximately 42% (S), 14% (S), 15% (C), 18% (C), and 2% (C), respectively. As discussed earlier it is not known whether the yield of DMS02 is being over- or underestimated. The total sulfur yield was 56% indicating that probably a major sulfur containing product has not been detected. With the inclusion of the contribution from DMSO the total carbon yield was 63%. The formation of DMSO and SO2 as products indicates that both, addition (13) and abstraction (14) pathways are operative,... 

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