TREND ANALYSES

BPCS/SIS functions that produce a trend analysis of input and output functions. Graphic video displays set-up to indicate process conditions and valve positions assure that the status of the process conditions is announced to the board operator, who may then verify the conditions with the field operator. 

Rate of change is the most often used trend analysis. Since most of the microprocessor-based systems provide the ability to automatically display broadband and narrowband data trends, analysts tend to rely on this means of comparative analysis. 

Subcase bl This case is encountered, for example, when batch records from different production campaigns are compared and the same number of samples was analyzed in each campaign. (Note under GMP, trend analysis has to be performed regularly to stop a process from slowly, over many batches, drifting into a situation where each parameter on its own is within specifications, but collectively there is the risk of sudden, global loss of control. Catastrophe theory has gained a foothold in physical and biological literature to describe such situations cf. Section 4.14.)... 

Table 4.39. Excerpt from Trend Analysis Table for Product BFG ... 

Figure 4.41. Trend analysis over 12 batches of a bulk chemical. The sieve analysis shows that over time crystals larger than 250 /urn were reduced from a weight contribution in the range of a few percent of the total to about 1% in favor of smaller sizes. Impurity C appears to follow the trend given by the lead compound for the competing side reaction 1. The very low moisture found for sample 3 could be due to a laboratory error because during drying one would expect ethanol to be driven off before water. Methanol is always below the detection limit.

Figure 4.42. Trend analysis over 46 batches of a bulk chemical produced according to the same manufacturing procedure Small and scaled-up batch size [kg], HPLC and Titration assays [%], resp. individual HPLC impurity levels [%], versus batch number. The lack of full correlation between assays indicates that the titration is insensitive to some impurities detected by HPLC. The mass balance, where available, suggests that all relevant impurities are quantified. Impurities B and C, for instance, are highly correlated (r = 0.884, p = 0.0002).

Jorgensen LA, Pedersen B. 1994. Trace metals in fish used for time trend analysis and as environmental indicators. Marine Pollut Bull 28 235-243. 

Stability is then considered as known and defined when Rf Uj is not significantly different from one. However the uncertainty calculated for the ratio RT based on the sum of CVs of two measurements carried out at two temperatures is a CV and not a confidence interval. In fact it does not consider the number of measurements carried out at the two temperatures and the use of this combined CV is not correct. In many cases it is an underestimation, as usually only two or three replicates are made. However, stability should be determined on the basis of a trend analysis, which is of importance also for any shelf life quantification see below. 

Roose P, Cooreman K, Vyncke W (1998) PCBs in cod Gadus morhua), flounder (Platichthysflesus), blue mussel (Mytilus eduUs) and brown shrimp Crangon crangon) from the Belgian continental shelf relation to biological parameters and trend analysis. Chemosphere 37 2199-2210. 

Of the various methods of data presentation, the one with which starting analysts may be least familiar is trend analysis and statistical quality control. In an industrial environment, analysis is often centered around the production of batches of material. The properties of those batches may change over time due to random effects or to subtle changes in the production process. In either case, the quality of the product may change. Analysis is used to track the change in the properties of batches over time. Industrial analytical methods, therefore, need to be extremely rugged. Millions of dollars may depend on the analyst s judgment as to batch equivalence. 

All deviations from the preset data should be documented, even if they are within the given tolerances. For the important process data, not only a comparison of the actual with the preset data is recommended, but also a trend analysis should be installed. This permits the recognition of systematic deviations long before the tolerances are exceeded. 

Consider the operations of a service company that markets and delivers seminars. Different aspects of this business, and hence its software requirements, can be described separately allocation of instructors and facilities to a seminar, on-time production of seminar materials for delivery, trend analysis for targeted marketing of seminars, invoicing and accounts receivable, and so on. 

Trend Analysis, Low-Dose Extrapolation, and NOEL Estimation... 

Trend analysis is a collection of techniques that have been discovered by toxicology since the mid-1970s (Tarone, 1975). The actual methodology dates back to the mid-1950s (Cox and Stuart, 1955). 

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