Sigma divided measures

Problems in using and interpreting sigma divided measures... 

Sigma divided measures should be avoided except where the problems with the data are so extreme (as for example in a meta-analysis combining different outcomes) that there is little alternative (Senn, 2006b). 

Determination of Alkaline Phosphatase Activity. Vomeronasal and olfactory epithelia were removed and transferred to 0.9% NaCl solution where they were maintained at 4°C. All soluble forms of enzymes were washed out from the surface of the receptor tissue (see Chukhrai et al., 1992 for details). Using procedures that are described in detail in Chukhrai et al. (1992), alkaline phosphatase activity in olfactory and vomeronasal epithelia was determined at pH=8.3 in 0.9% bicarbonate buffer. Disodium p-ni-trophenol phosphate (Sigma) was used as a substrate its initial concentration was 8.1 x 10" M in the buffer. The increase of p-nitrophenol (the product of p-nitrophenylphosphate hydrolysis) was measured with a double-beam spectrophotometer at 400 nm every 30 sec. The velocity of the reaction was determined by estimating the angle of the slope (optical units [OU]/min). The obtained values were divided into the extinction coefficient (C ) under corresponding pH values to obtain the reaction velocity values in pM/min. Effective parameters of the Michaelis-Menten equation were compared using standard procedures (Chukhrai et al., 1992). 

The basics rely on the assumption that outcomes of most processes will follow a normal distribution, the bell-shaped curve shown in Figure 28.11. Each normal distribution is specified by a mean and a standard deviation symbolized by the Greek letter sigma, o. The mean (called X-bar) is the average of all the process outcomes the standard deviation is a measure of the variation from the mean. The mean is calculated by adding all the outcomes and dividing by the number of observations. The mean of 1, 2, and 3 is (l+2+3)/3 = 2. 

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