Proxy variables

UNODC has also started to conduct yield surveys in some countries, measuring the yield of test fields, and to develop methodologies to extrapolate the yields from proxy variables, such as the volume of poppy capsules or the number of plants per plot. This approach is used in South-East Asia as well as in Afghanistan. All of this is intended to improve yield estimates, aiming at information that is independent from farmers reports. The accuracy of the calculated yields depends on a number of factors, including the number of sites investigated. In the case of Afghanistan the confidence interval for the mean yield results in the 2006 survey was, for instance, +/- 3% of the mean value (tt= 0.1). 

Age is both an observable and a universal demographic descriptor. It is frequently a substitute or proxy variable for physical fitness, activity levels, interests and previous travel experiences. 

Significant proxy variables may be used within limits with some success as predictors and still not have any retd physical significance. A good example is corrosion rates that correlate with distance from a seashore when the actual cause is the amount of salt spray deposited on the specimens. 

Fig. 1-2 Chemical data from the Vostok ice core. The graph of 5D can be taken as a proxy for temperature changes, as described in Chapter 18. CO2 and CH4 are greenhouse gases and vary in the same direction as temperature. Non-seasalt sulfate and methane sulfonic acid are both sulfur species existing in the particle phase, and are positively correlated with each other, but negatively with T. Major variations for all of these variables seem to correlate either positively or negatively with each other, indicating a coupled system. <5D, non-seasalt sulfate, and methane sulfonic acid data kindly provided by Dr Eric Saltzman. CO2 data are from Bamola et al. (1987) and Jouzel et al. (1993). CH4 data are from Chappellaz et al. (1990) and Jouzel et al. (1993). (ppmv = parts per million by volume ppbv = parts per billion by volime)...

Barnes CE, Cochran JK (1993) Uranium geochemistry in estuarine sediments Controls on removal and release processes. Geochim Cosmochim Acta 57 555-569 Berkman PA, Foreman DW, Mitchell JC, Liptak RJ (1992) Scallop shell mineralogy and crystalline characteristics Proxy records for interpreting Antarctic nearshore marine hydrochemical variability. Contrib Antartic Research 57 27-38... 

Black shales that are formed in an anoxic environment such as the Black Sea have a Mo isotope composition nearly identical to ocean water (Barling et al. 2001 Arnold et al. 2004 Nagler et al. 2005). Organic carbon rich sediments formed in suboxic environments have variable Mo/ Mo ratios intermediate between those of ocean water and oxic sediments (Siebert et al. 2003). Thus Mo isotope values in ancient black shales can be used as a paleo-oceanographic proxy of the oxidation state of the ocean, as for example has been discussed by Arnold et al. (2004) for the Proterozoic. Figure 2.25 summarizes natural Mo isotope variations. 

Elevation predictions from tectonic models alone only provide simple guidance because topography is the product of complex reactions among climate, erosion and tectonics. Paleoelevation techniques discussed in this volume measure different aspects either directly or indirectly of topography some techniques are sensitive to local elevation, some to relief, and some rely on proxies of environmental variables. Future directions may include measurement of different variables of the tectonic-climate-erosion system independently from one another and understanding the interaction between them. From these relationships, directly or indirectly, the geodynamic processes may be further constrained. 

It is essential to understand the isotopic variability within authigenic minerals that form the basis of terrestrial paleoclimate records and between such samples that are isochronous within an outcrop of a stratigraphic formation. Except for variability studies in biogenic materials (teeth, bone, shells) (e.g., Kohn et al. 2002), we know of no paleoaltimetry studies that have examined this natural variability in authigenic or pedogenic proxy materials. Such variability studies should be conducted before any quantitative estimates of paleoelevation can be made. 

Nationality is a widely used demographic descriptor in tourism studies. It is sometimes an observable characteristic with physical appearance, clothing styles, and tour party characteristics providing identifiable markers of nationality. Like age, nationality is often used by tourism researchers as a proxy or substitute variable. In particular, it is often used as an indicator of the cultural allegiance or roots of the tourist. Nationality is sometimes measured, although not very accurately, by establishing the tourists country of residence. 

Cause-and-effect relationships should be chosen for investigation, rather than proxy ones or, as is so common, effect-and-effect ones. Levels should be selected for truly independent and uncoupled variables that will avoid either a vanishingly small or a swamping or overwhelming response that would mask or even obliterate some other response of importance or interest. This will sometimes necessitate the use of unconventionally designed or even unbalanced blocks of experiments. 

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