Quartile Method

It was shown later that a mass transfer rate sufficiently high to measure the rate constant of potassium transfer [reaction (10a)] under steady-state conditions can be obtained using nanometer-sized pipettes (r < 250 nm) [8a]. Assuming uniform accessibility of the ITIES, the standard rate constant (k°) and transfer coefficient (a) were found by fitting the experimental data to Eq. (7) (Fig. 8). (Alternatively, the kinetic parameters of the interfacial reaction can be evaluated by the three-point method, i.e., the half-wave potential, iii/2, and two quartile potentials, and ii3/4 [8a,27].) A number of voltam-mograms obtained at 5-250 nm pipettes yielded similar values of kinetic parameters, = 1.3 0.6 cm/s, and a = 0.4 0.1. Importantly, no apparent correlation was found between the measured rate constant and the pipette size. The mass transfer coefficient for a 10 nm-radius pipette is > 10 cm/s (assuming D = 10 cm /s). Thus the upper limit for the determinable heterogeneous rate constant is at least 50 cm/s. 

This method gives those subjects who withdraw for positive reasons the best possible outcome value for the endpoint and those who withdraw for negative reasons, the worst value. This may seem a little extreme and a lesser position would be to look at the distribution of the endpoint for the completers and to use say the upper quartile (the value that cuts off the best 25 per cent of values) for those subjects withdrawing for positive reasons and the lower quartile (the value that cuts off the worst 25 per cent of values) for those subjects who withdraw for negative reasons. 

Method No. Bond Distances Mean Median Minimum Maxiumum Range Lower Quartile Upper Quartile Interquartile Range Standard Deviation... 

The second quartile (median) and inter-quartile range can be used as an alternative method for describing the central tendency and dispersion of a set of measured data. Both are robust and can be useful where there are occasional extreme values. 

The box plot has proved to be a popular graphical method for displaying and summarizing univariate data, to compare parallel batches of data, and to supplement more complex displays with univariate information. Its appeal is due to the simplicity of the graphical construction (based on quartiles) and the many features that it displays (location, spread, skewness, and potential outliers). Box plots are useful for summarizing distributions of treatment outcomes. A good example would be the comparison of the distribution of response to treatment at different dose levels or exposure (as measured by area under the plasma concentration-time curve) as in Figure 37.3. 

It can be noted that in all versions of Excel , the method defined by Eq. (1.7) is available (as either the function quartile or quartile. inc). Newer versions of Excel (2010 or newer) also support option 1 (as quartile.exe). All versions of MATLAB implement option 2. 

The results of one case control study of 69 women suggests that serum BPA levels may be associated with the occurrence of endometriosis (Cobellis et al. 2009) but the smdy was limited by a small sample size and the selected methods for measurement of serum BPA. Future studies of endometriosis risk should evaluate BPA exposure using 24-h urine samples. In a study of 137 women undergoing IVF, higher quartiles of urinary BPA concentrations were associated with increased odds of implantation failure (Ehrlich et al. 2012a). 

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