On Factors And Components: A Comment on Nicholson and Yeates

Un article recent par Nicholson et Yeates sur l'ecologie factorielle de la ville de Winnipeg met en lumiere une difficulte courante dans la litterature - c'est-a-dire une confusion entre la methode des composantes principales et celle de l'analyse factorielle. Elles ne sont point identiques. Puisque les deux auteurs ne precisent pas lequel de ces deux modeles statistiques ils ont utilise, leurs resultats sont difficiles d'interpretation. Cependant, nous sommes portes a croire qu'ils auraient employe la methode des composantes principales. Si c'est le cas, leurs conclusions ne sont pas directement comparables a celles des autres études, puisque la plupart des autres chercheurs oeuvrant dans ce secteur ont favorise l'analyse factorielle. En dernier lieu, l'auteur suggere un ensemble de regies a respecter dans la production des rapports de recherches se rapportant a des etudes factorielles et a des etudes de composantes.
A recent article by Nicholson and Yeates on the factorial ecology of the city of Winnipeg illustrates a problem not uncommon in the literature - a confusion between the method of principal components and the principal factor procedure. They are not the same. Since the authors do not clearly state which of the two statistical models they employed, their results are difficult to interpret, although the available evidence suggests that they did use a principal component solution. If so, their results are not directly comparable to those reported by others, since most other investigators in the area have used the principal factor procedure. Finally, a set of rules for the reporting of component and factor studies is suggested.     

Community attitudes on the family of issues surrounding the death of terminal patients

In two studies, respondents made recommendations for the medical treatment of a terminally ill elderly woman. The woman was or was not experiencing intractable pain, and had requested either heroic medical efforts or euthanasia. Respondents' recommendations were influenced by both the specific wishes of the patient and the pain the person was experiencing. However, participants were not completely swayed by the patient's wishes: only about half of the sample recommended euthanasia even when the patient was in intractable pain and had requested death; also, many subjects would not resuscitate the patient whose heart or lungs failed, even though she had requested heroic measures. Respondent attitudes toward euthanasia predicted recommendations in the expected directions. We suggest that there is less dissent on the issues that arise for medical treatments at the end of life than has been widely assumed.     

Population and land use change in the California Mojave: Natural habitat implications of alternative futures

Demographic and land use dynamics have important implications for the natural environment within both developed and developing nations. Within the context of developed nations, popular and policy debates surrounding contemporary patterns of suburbanization attest to the salience of demographic and development issues. We examine the implications of land-use patterns as related to population and development within the context of the California Mojave Desert ecosystem. In a general sense, we aim to better understand the land requirements inferred by varying levels of population growth and density, as well as the natural habitat implications of those requirements. We develop a GIS including remotely sensed imagery, and demographic, economic, and biophysical data to examine of the implications of various demographic scenarios on species diversity. Spatial and statistical models are designed to develop possible alternative land use `futures'. Within the context of the California Mojave region, our results suggest that high-density development could reduce conflict with regions providing potential habitat for threatened or endangered species by over 80 percent. The process of model development demonstrates a potentially useful tool for policymakers, allowing for estimation and visualization of the land use implications of policy decisions.     

Factorial ecology: A critique and some suggestions

Studies in factorial ecology have typically used the principal factor procedure coupled with varimax rotation. Since it can be shown that the results one obtains vary according to the factor and rotation models he employs, and since there is no one “best” way of obtaining initial and derived factor solutions, it is proposed that future research in the area adopt an approach involving the simultaneous use of several different computing algorithms for obtaining initial solutions and both orthogonal and oblique rotation procedures to avoid the possibility that the results one obtains are not method-dependent. Ideally, the factor models employed should differ maximally with respect to the principles upon which they are based. If one finds a given factor regardless of the method he uses, only then can he assert with any confidencethat it is not an artifact of his method. Factorial ecologists are often interested in computing “factor scores”, but “true” factor scores are not uniquely computable; they can only be estimated. Since the proposed research strategy involves using either a component or an image model, in which the corresponding scores are exact and uniquely computable, the factor score problem is, in a sense, solved. Next it is suggested that, by using orthogonal solutions, factorial ecologists may be overlooking a very important piece of information—the correlation between the factors. There is some reason to believe that this varies from city to city, and may account for the fact that some factors which emerge in studies of Western cities are sometimes not found in cities elsewhere. Some comments are also made on the value of using census tract data, and on the availability of computer programs for different initial and derived factor solutions.