Principal curves revisited

A principal curve (Hastie and Stuetzle, 1989) is a smooth curve passing through the middle of a distribution or data cloud, and is a generalization of linear principal components. We give an alternative definition of a principal curve, based on a mixture model. Estimation is carried out through an EM algorithm. Some comparisons are made to the Hastie-Stuetzle definition.     

Brief case: managing inputs

Jane Carmichael's views on Managing Inputs provide a further interesting contribution on a topic, strategic control, that we have covered on several occasions in this column. Carmichael's approach is to dig back behind the results being achieved to the 'inputs' on which they depend. But, while this may unearth causes of performance that can often be missed by a bottom-line orientation, results must ultimately remain vital; a business that is on track with all its input measures, but is missing its output goal is still in trouble. We continue to be interested in hearing from readers with views on strategic control processes, particularly those who have found productive ways of setting input and output targets.     

National Practitioner Data Bank--incomplete and future cloudy

Nearly six years after the National Practitioner Data Bank was authorized by Congress in the Health Care Quality Improvement Act of 1986, and more than a year after its actual creation, the device is still only partially operational. What is more, the success of even those limited efforts is being questioned, and the timetable for future developments remains to be firmed up. Also, the costs are much higher than estimated.     

Clinical program renovation management

The day-to-day management of medical practice is so heavily influenced by tactical imperatives that few physicians have the time to think strategically. Traditionally, the difference between tactics and strategy is not a major concern of most physician executives. The realm of tactics is the short run, when managers must make do with the fixed resources at hand. Strategy addresses the long run, when all resources and markets are variable. A tactical focus is understandable, maybe even acceptable, in industries where nothing challenges traditional approaches to production of an established product or service. However, medical care in the 1990s is changing so fast that a physician executive must devote an incredible amount of time and effort just to stay confused about what is going on.     

Immigrant fertility: an examination of social characteristics and assimilation

"This study compares the fertility patterns of foreign-born and native-born women in Canada and examines whether [the] same set of social characteristics accounts for differential fertility among both the groups. The study also assesses the importance of social characteristics and assimilation on immigrant fertility behavior. Two generations of currently married/cohabiting women with spouse present are analyzed using multiple regressions. The results reveal similar effects on fertility of social characteristics for foreign-born and native-born, while in the case of younger generations the effects are stronger."     

European Community legislation and intergovernmental cooperation on migration

Recent trends in migration policy in the European Community are outlined. The focus is on the need to increase cooperation between the member states and to increase the power of the Community's Court of Justice in decision-making about migration and refugee policy.     

The spatial and socio-occupational mobility of the population

The author describes topics included in a study of spatial, social, and occupational mobility in Poland. These include rural migration, the effect of the family life cycle on migration, the social impact of migration, the effect of migration on spatial distribution, and migration prospects until the end of this century.     

Stochastic modelling of regional annual rainfall anomalies in East Africa

ARIMA (p, d, q) models were fitted to areal annual rainfall of two homogeneous regions in East Africa with rainfall records extending between the period 1922–80. The areal estimates of the regional rainfall were derived from the time series of the first eigenvector, which was significantly dominant at each of the two regions. The first eigenvector accounted for about 80% of the total rainfall variance in each region.

The class of ARIMA (p, d, q) models which best fitted the areal indices of relative wetness/dryness were the A R M A (3, 1) models. Tests of forecasting skill however indicated low skill in the forecasts given by these models. In all cases the models accounted for less than 50% of the total variance.

Spectral analysis of the indices time series indicated dominant quasi-periodic fluctuations around 2.2–2.8 years, 3–3.7 years, 5–6 years and 10–13 years. These spectral bands however accounted for very low proportion of the total rainfall variance.