Accuracy of Estimates

At each phase of a project cost information is required to enable decisions to be taken. In the conceptual phase these estimates may be very approximate (e.g. + 35% accuracy), reflecting the degree of uncertainty regarding both reservoir development and surface options. As the project becomes better defined the accuracy of estimates should improve. 

Types and Accuracy of Estimates Capital-cost estimates may be required for a variety of reasons, among others to enable feasibility studies to be carried out, to enable a manufacturing company to select from alternative investments, to assist in selection from alternative designs, to provide information for planning the appropriation of capital, and to enable a contractor to bid on a new project. It is therefore essential to achieve the greatest accuracy of estimation with a minimum expenditure of time and money. 

Greater accuracy of estimation may be achieved, within limits, by the expenditure of more time and money. The greater the accuracy required, the greater the time and effort needed to obtain the design and cost data prior to making the estimate. 

W. R. Park investigated the cost and accuracy of estimates for a projec t with a total cost of 1 million as shown in Fig. 9-41 Co.st Engi-... 

The experimental reaction rate computations based on equation (4) are primarily functions of the computed average solution temperature (T ). The kinetic model rate computations based on equation (1) or (2) are primarily functions of both "T " as well as the estimated conversion(s). Earlier we explained why we expected decreasing accuracies of estimating both the conversions and the average solution temperature in Tests 1, 2 and 3 respectively. 

We present a general approach for estimating relative permeability and capillary pressure functions from displacement experiments. The accuracy with which these functions are estimated will depend on the information content of the measurements, and hence on the experimental design. We determine measures of the accuracy with which the functions are estimated, and use these measures to evaluate different experimental designs. In addition to data measured during conventional displacement experiments, we show that the use of multiple injection rates and saturation distributions measured with MRI can substantially increase the accuracy of estimates of multiphase flow functions. 

We also use a linearized covariance analysis [34, 36] to evaluate the accuracy of estimates and take the measurement errors to be normally distributed with a zero mean and covariance matrix Assuming that the mathematical model is correct and that our selected partitions can represent the true multiphase flow functions, the mean of the error in the estimates is zero and the parameter covariance matrix of the errors in the parameter estimates is ... 

Results of the covariance analysis for the accuracy of estimates of the relative permeability of water and capillary pressure functions, along with the specified true functions, are shown in Figures 4.1.9 and 4.1.10 (the results for the relative permeability of oil are not included here). The accuracy measures are presented as 95 % confidence intervals. 

In the work described earlier, the applicability of the Weibull model was further tested by assessing the precision of estimation [expressed by the CV defined as the standard error of estimates divided by the estimated value] and the relative accuracy of estimation of the model parameters (based on the difference of the estimates from the actual value, divided by the actual value). Regarding the precision of estimates, for data with SD = 2 the maximum CV value for Wo, b, and c was 13%, 52%, and 16%, respectively, whereas the corresponding numbers for data with SD = 4 were 33%, 151%, and 34%, respectively. As expected, the precision of the estimates decreases as the SD of the data increases, with the poorest precision for the b estimates and the best for the Wo estimates. Additionally, the maximum CV values were associated with low c values (c = 0.5). 

The relative accuracy of estimation is illustrated in Figure 3 by the box plots obtained from the individual data sets. On the basis of Figure 3, the accuracy of the estimates decreases with the data variability. 

In general, the accuracy of estimating temperatures by measuring the kinetic isotope effect may be influenced by the following factors (1) the accuracy of the semiclassical model, (2) the lesser sensitivity of the isotope effect at higher temperatures, and (3) the reactions of H (and D) atoms competing with spin trapping. 

Shor, R. The accuracy of estimating the relative difficulty of typi cal... 

According to the National Research Council of the National Academy of Science, risk assessment consists of four broad but interrelated components hazard identification, dose-response assessment, exposure assessment, and risk characterization, as depicted in Figure 24.1. The reader should, however, be aware that these risk assessment activities can provide research needs that improve the accuracy of estimating the risk or probability of an adverse outcome. 

The analyzed approach to finding the optimum indicates that the model must have a possibility to estimate the direction of further design points with associated precision. Since we are unaware of the direction of movement towards the optimum before defining the model, the accuracy of estimation of the mathematical model must be the same in all directions. This is to say that estimated values in experiment region may differ from the real, measured response values for the previously given magnitude. The model which fulfills this requirement is called adequate, to be discussed in a separate section. 

Studies by Kondratyev et al. (2004a, b) showed that consideration of the spatial heterogeneity of sinks and sources of atmospheric carbon and specification of the parameters of its fluxes at the atmosphere-land and atmosphere-ocean boundaries raised the accuracy of estimates, but did little to remove either imbalances or differences between carbon fluxes and the dynamics of the change in C02 partial pressure in the terrestrial atmosphere. 

All of this suggests the conclusion that Arctic waters remove carbon dioxide from the atmosphere. Therefore, once again a detailed study of this process is needed before a global model of carbon cycle can be specified, thereby improving the accuracy of estimation of the greenhouse effect due to emissions of anthropogenic... 

Study estimate also called factored estimate . When studies are more advanced, the factored estimate may take into account the detailed equipment characteristics. Once the individual costs are determined, they may be multiplied by a number of factors for installation, piping and services, instrumentation and control and eventually by date and geographic location factors. Probable accuracy of estimate is about +25-30%. 

Detailed estimate (contractor s estimate) based on complete engineering drawings, specifications and site surveys. Probable accuracy of estimate is about +5%. 

For exposure assessors, uncertainty analysis increases transparency and, thereby, the credibility of the process. Consequently, reliance on worst-case assumptions can be reduced and decision support improved. Uncertainty analysis also identifies important data gaps, which can be filled to improve the accuracy of estimation. 

To seek a reasonable accurate analytical approximation for the available area, as a function of 6S = Nsnr /A and 6y = Nynr /A one should have accurate values for a reasonable number of coefficients in the low-density expansion of the binaiy RSA model, which is not a trivial task. Even for binaiy mixtures of disks at equilibrium, a problem that received much more attention than RSA, analytical expressions are known only for the first three terms of the virial expansion [21], The values of the fourth and fifth terms, obtained using laborious numerical calculations, were reported only for a few values of y and molar fractions of the two types of disks [22], In the non-equilibrium RSA of binaiy particles, one should take into account, when calculating the higher terms of the series, not only various y and molar fractions, but also the order of deposition of particles. Furthermore, as already noted, it is not clear whether the involved calculations needed to obtain the next unknown terms of the low-density expansion would improve much the accuracy of estimating the jamming coverage. 

Figure 3. Accuracy of estimation of the selectivities for styrene (ST), benzaldehyde (BA), benzene + toluene (B + T), CO and COj by a neural network (left) in comparison with the selectivity for styrene as estimated by an expert system, INCAP (right) (reproduced by kind permission of T. Hattori).

Order-of-magnitude estimate (ratio estimate) based on similar previous cost data probable accuracy of estimate over 30 percent. 

Study estimate (factored estimate) based on knowledge of major items of equipment probable accuracy of estimate up to 30 percent. 

Preliminary estimate (budget authorization estimate scope estimate) based on sufficient data to permit the estimate to be budgeted probable accuracy of estimate within +20 percent. 

Definitive estimate (project control estimate) based on almost complete data but before completion of drawings and specifications probable accuracy of estimate within 10 percent. 

Probable accuracy of estimate-Net profit after % taxes ... 

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