Various types of bias

Judging environmental and health hazards objectively is a very difficult task because of the numerous ways bias can affect decisions. The misjudgments may be caused by insufficient scientific methods, by influence from media and organized groups fighting for a better environment, or from industry lobbyists. We shall summarize some of these problems in this chapter. 

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Various types of BIAs are produced from L-tyrosine via (5)-reticuline in plants. (5)-Reticuline is a key intermediate of the biosynthesis of BIAs. The biosynthetic pathway of (5)-reticuline from L-tyrosine is shown in Scheme 1.1 and has nine steps ... 

Bias. (1) A point of view that prevents impartial judgement on issues relating to that point of view. Clinical trials attempt to control this through double blinding. (2) Any tendency for a value to deviate in one direction from the tme value. Statisticians attempt to prevent this type of bias by various techniques, including randomization. 

In this review we point out briefly the various instrumentation factors important in obtaining mass spectra of inorganic and organometallic compounds and in affecting the quality of spectra observed. Selected examples are chosen, admittedly with a personal bias, to illustrate the various types of information available from mass spectra. We have... 

Fig. 2.1 The influence of the various types of errors on the flnal result of the measurement Ax y bias, Ax random error for a single measurement, o,- gross error, /ix expected (true) value, x,-measurement result, x mean value of the series of measurement results, and Ax random error for a series of measurements...

When chance, bias and confounding are considered unlikely, causation is possible but still cannot be assumed as an explanation for an association based on non-randomised data. Often there may be a series of studies or various types of data which bear on this question. In this context, nine criteria first described by Bradford-Hill in the 1960s are stiU used. These may be summarised as follows ... 

Fuel feeder/distributors that evenly feed the fuel over the entire grate surface are necessary for even energy rerelease. These feeder/distributors can be mechanical, pneumatic, or a combination of both and must be placed across the width of the front of the stoker in sufficient quantity to achieve even lateral distribution of the fuel and have the means to longitudinally adjust fuel distribution for various types of fuels and sizing. They should be able to bias the feed rate one feeder to another, and to adjust for segregation of fuel sizing from one feeder to another. The performance of the fuel feeder/ distributors can adapt to the different characteristics of solid fuels which plays a major part in the ability to operate at lowest possible emissions and highest combustion efficiency (Johnson, 2002). 

Systematic errors arise not only from procedures or apparatus they can also arise from human bias. Some chemists suffer from astigmatism or colour-blindness (the latter is more common amongst men than women) which might introduce errors into their readings of instruments and other observations. Many authors have reported various types of number bias, for example a tendency to favour even over odd numbers, or 0 and 5 over other digits, in the reporting of results. It is thus apparent that systematic errors of several kinds are a constant, and often hidden, risk for the analyst, so the most careful steps to minimize them must be considered. 

Fig. 3.40 Spatial distribution of noise generation density in an extraction-type diode for various values of bias...

Fig. 9 (a) Three types of single conductance traces for Au atomic contacts as observed in the presence of specifically adsorbed anions characterized by well-developed plateaus (curves A), noisy plateaus (curves B), and abrupt steps with no plateaus (curves C), respectively. The stretching rate was 60 nm s 1. and bias voltage applied was 0.100 V. (b,c) All data-point conductance histograms at various electrode potentials in the presence of specifically adsorbed S042- (b) and Cl- (c), respectively... 

Much of the discussion of this subsection has been based on the behavior of hydrogenated diodes annealed under reverse bias. Annealing under forward bias has also been studied, though less extensively, and some of the observations have suggested the possibility of a new type of thermal breakup of BH complexes, namely BH + e— B + H° (Tavendale et al., 1985, 1986a). These authors reported breakup of BH in a few hours at 300 K under forward bias, both in Schottky diodes and in n+-p junctions. However, in a similar experiment with an n+-p junction, Johnson (1986) found a slight buildup of BH under forward-bias anneal. Available details of the various experiments are too sketchy to allow useful speculation on the reasons for the different outcomes or possible mechanisms for accelerated breakup. 

The last type of precision study is reproducibility, which is determined by testing homogeneons samples in mnltiple laboratories, often as part of interlaboratory crossover stndies. The evalnation of reprodncibility results often focuses more on measnring bias in resnlts than on determining differences in precision alone. Statistical eqnivalence is often nsed as a measnre of acceptable interlaboratory resnlts. An alternative, more practical approach is the nse of analytical equivalence, in which a range of acceptable resnlts is chosen prior to the study and used to judge the acceptability of the results obtained from the various laboratories. 

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