Peeters, Edwin T.H.M., et al. 2009. Assessing ecological quality of shallow lakes: Does knowledge of transparency suffice? Basic and Applied Ecology 10(1): 89–96. doi:10.1016/j.baae.2007.12.009
The authors aim to identify what is the simplest way to assess “ecological quality” of aquatic ecosystems, focusing here on shallow European lakes. They are motivated by other approaches to the European Water Framework Directive (WFD), which “requires that all aquatic ecosystems in their member states should reach ‘good’ ecological quality by 2015.” Other approaches employ a slew of variables to assign each lake to one of five quality classes (Bad—High), as required by the WFD, using biological, physical, and chemical indicators. The authors hope to identify a shortcut to quality assignment, one not requiring so many variables. They seek a shortcut by performing a multinomial logistic regression to attempt to isolate the variable best explaining quality variation. As it turns out, Secci depth (essentially the depth at which a particular submerged disc is visible, and thus a measure of water clarity) corresponds best to ecological quality.
In performing this analysis, the authors face a kind of Third Man Problem: if you want to discern which empirical properties are best associated with variance in ecological quality, you need some further measure of ecological quality. Recognizing this, the authors’ strategy is to use experts’ evaluations of ecological quality. They make this the dependent variable in their regression.