Bias, concept

The fluid mechanics origins of shock-compression science are reflected in the early literature, which builds upon fluid mechanics concepts and is more concerned with basic issues of wave propagation than solid state materials properties. Indeed, mechanical wave measurements, upon which much of shock-compression science is built, give no direct information on defects. This fluids bias has led to a situation in which there appears to be no published terse description of shock-compressed solids comparable to Kormer s for the perfect lattice. Davison and Graham described the situation as an elastic fluid approximation. A description of shock-compressed solids in terms of the benign shock paradigm might perhaps be stated as ... 

This concept is demonstrated schematically in Figure 1.11. It can be seen that the initial bias in a system of proteins containing two conformations (square and spherical) lies far toward the square conformation. When a ligand (filled circles) enters the system and selectively binds to the circular conformations, this binding process removes the circles driving the backward reaction from circles back to squares. In the absence of this backward pressure, more square conformations flow into the circular state to fill the gap. Overall, there is an enrichment of the circular conformations when unbound and ligand-bound circular conformations are totaled. 

It is probably fair to say that the academic studies conducted on the differences between formal and informal mentoring have an American bias. You might not perceive this as a big deal, but when you think back to the section in Chapter 1 regarding the different concepts of mentoring in America and Europe, you will appreciate the significance. Just to remind you, the American view of mentoring emphasizes protection and sponsorship, whilst the European view favours the mentee s insight and... 

The most intriguing aspect of the self-spreading lipid bilayer is that any molecule in the bilayer can be transported without any external bias. The unique characteristic of the spreading layer offers the chance to manipulate molecules without applying any external biases. This concept leads to a completely non-biased molecular manipulation system in a microfluidic device. For this purpose, the use of nano-space, which occasionally offers the possibility of controlling molecular diffusion dynamics, would be a promising approach. 

Fraser has extensively discussed this relationship between laboratory work and clinical needs (Fraser and Hyltoft Peterson 1993) and has recently addressed the role of documented analytical quality as derived from measurements of RMs (Fraser and Hyltoft Peterson 1999). Among the concepts proposed by Fraser and his colleagues, it is suggested that analytical imprecision should be <0.50 CVi and bias should be <0.25 (CVi + where CVj is the within-subject biological variation (i.e. changes from day to... 

There are other trial design concepts for you to be aware of. A clinical trial can be carried out at a single site or it can be a multi-center trial. In a single-site trial all of the patients are seen at the same clinical site, and in a multi-center trial several clinical sites are used. Multi-center trials are needed sometimes to eliminate site-specific bias or because there are more patients required than a single site can enroll. 

Accuracy and trueness have been defined above and it was mentioned that these terms base on qualitative concepts (ISO 3534-1 [1993]). If it is necessary to have quantitative information, the bias, which is a measure of inaccuracy, should not be used to quantify accuracy and trueness, respectively. Instead of this, the following measures might be applied... 

We will begin by taking a look at the detailed aspects of a basic problem that confronts most analytical laboratories. This is the problem of comparing two quantitative methods performed by different operators or at different locations. This is an area that is not restricted to spectroscopic analysis many of the concepts we describe here can be applied to evaluating the results from any form of chemical analysis. In our case we will examine a comparison of two standard methods to determine precision, accuracy, and systematic errors (bias) for each of the methods and laboratories involved in an analytical test. As it happens, in the case we use for our example, one of the analytical methods is spectroscopic and the other is an HPLC method. 

The concepts of precision, bias and accuracy were introduced in Chapter 4. However, as they are important in the context of evaluating measurement uncertainty it is worth revisiting them. 

In spite of the numerous strengths that assessment brings to the treatment of a drug problem, many measures are culturally limited. Cultural bias of measures may be one of the most poorly understood concepts in the treatment community. Researchers have discovered over time that assessment can be culturally biased in a number of ways, some that are quite obvious and others that are much more subtle. These biases can negatively affect the treatment of minority clients by producing false information about the clients and their drug problems, which in turn... 

Cultural bias. The concept that assessment is biased, either overtly or covertly, by the cultural values and language in which it is developed. 

If a large number of readings of the same quantity are taken, then the mean (average) value is likely to be close to the true value if there is no systematic bias (i.e., no systematic errors). Clearly, if we repeat a particular measurement several times, the random error associated with each measurement will mean that the value is sometimes above and sometimes below the true result, in a random way. Thus, these errors will cancel out, and the average or mean value should be a better estimate of the true value than is any single result. However, we still need to know how good an estimate our mean value is of the true result. Statistical methods lead to the concept of standard error (or standard deviation) around the mean value. 

Here the concept of statistical control is not applicable. It is assumed, however, that the materials in the run are of a single type. Carry out duplicate analysis on all of the test materials. Carry out spiking or recovery tests or use a formulated control material, with an appropriate number of insertions (see above), and with different concentrations of analyte if appropriate. Carry out blank determinations. As no control limits are available, compare the bias and precision with fitness-for-purpose limits or other established criteria. 

Receive briefings from the PMACWA technical staff concerning the EDS II testing plan and the Blue Grass demilitarization program status. Develop concept draft for the Pueblo letter report. Continue development of the EDS II first full message draft. Conduct a bias discussion update. 

Rigorous correction for instrumental mass bias is required if the precision of an isotope ratio measurement needs to be greater than l%o per mass unit. This concept is well illustrated by the definitive Ca isotope work of Russell et al. (1978), which used a double-spike approach. Prior to the Ca isotope investigation of Russell et al. (1978), natural mass-dependent Ca... 

The purpose of utilising an ITT analysis population is to minimise the bias that can occur by excluding patients who do not complete a trial. The late Prof Ken McRae iUustrated the concept using the following simple example. 

As in the above example in which the wine quality is a somewhat ill-defined concept subject to individual taste, many classification schemes are often heavily biased by the viewpoint of the researcher (and this can influence the performance). Unsupervised learning (e.g. Ritter et al., 1992) largely avoids this bias but at the cost of often less powerful methods and the missing interpretation of the arising classes, where often it is not obvious what these classes represent. 

Bias The systematic or persistent distortion of an estimate from the true value. From sampling theory, bias is a characteristic of the sample estimator of the sufficient statistics for the distribution of interest. Therefore, bias is not a function of the data, but of the method for estimating the population statistics. For example, the method for calculating the sample mean of a normal distribution is an unbiased estimator of the true but unknown population mean. Statistical bias is not a Bayesian concept, because Bayes theorem does not relay on the long-term frequency expections of sample estimators. 

Thus, Lind showed the importance of the comparative trial and Evans and Hoyle showed the importance of the placebo effect in evaluating drug response. Gold et at. then showed the importance of observer bias and introduced the concept of the double-blind study in 1937 in a study of treatments for angina patients. They wrote ... 

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