Surveys and decisions in the context of multidisciplinary programmes: estimators and indicators

Scientific programmes whose objectives are to provide pertinent knowledge a nd information for sustainable use of a natural resource always include dat a collection operations. Functions of the data collected axe obtained from surveys. These functions (estimators) are formulae constructed according to the survey's model defined by the design of the survey and the sample sele ction procedures. In complex designs, a 'superpopulation model' is always p resent. This model, accounting for available knowledge on the observed syst em, is defined by assumptions on the distribution of the collected data. Users consider not only the quality of the estimates (outputs of the survey ) but also, and possibly primarily, the quality of these estimates as input (information) to their own decision frameworks, which also constitute a su perpopulation model. Hence, a survey combines at least two models; a survey model and a user's model. These different models are discussed in this paper with the help of three e xamples that differ in the types of system under study, in the objectives o f the surveys, and in the nature of the collected information, Specific fun ctions of the collected survey data may be considered as estimators when co nsidered as output of the survey model and as indicators when considered as input to the user's model. A user may build indicators from many sources of information and, as severa l different users may use the estimates, a survey is an element of an infor mation system. Analysis of data leads to improved knowledge of the system u nder study and to the better identification of the various associated model s. Therefore, surveys are elements of dynamic systems in which theory and p ractice are complementary. Although classical sampling theory often appears not to be sufficient in this global context, it remains necessary. The use of information from different sources to be used from different points of view implies an increased level of rigour with many models, all of which mu st be explicitly defined. (C) 2001 Elsevier Science B.V. All rights reserve d.