Retrospective questions: data quality,task difficulty,and the use of a checklist

Data from a national panel study with waves in 1987 and 1991 (N=1257), present evidence of the low accuracy of responses to retrospective questions, concerning both attitudes and behaviour. Applying a split ballot design, it is investigated whether using a checklist improves the response accuracy for a retrospective question about one single event: how respondents (N=363) did obtain the job they had four years ago. Furthermore interaction effects of ‘task difficulty’ are examined. The response accuracy indeed increases by using a checklist; however, this increase is not statistically significant. The expected increase of the checklist effect with higher ‘task difficulty’ appears for longer recall intervals, but not for more frequent changes of jobs. It turned out that for male respondents all the predicted effects are indeed clearly present. But for female respondents the checklist appeared to have no effect, irrespective of the task difficulty. A tentative explanation for this unexpected gender effect is suggested by pointing at indications that the male and female respondents differed in the way they obtained their job.     

On the existence of bivariate moments of lower order given the existence of moments of higher order

Dit artikel geeft een voorbeeld van een twee-dimensionale waarschijnlijkheidsdcht-heid met de eigenschap, dat het bestaan van momenten van de vorm E(g^ky^l ) niet het bestaan garandeert van alle momenten van lagere orde, E(g^myⁿ ) met 0myⁿ ) met 0 < m < k en 0 < n < l is, dat de drie momenten E(x^k), E(y^l ) en E(x^ky^l ) bestaan, alsmede een iets algemener resultaat.     

Efficiency. of infinite dimensional M- estimators

It is well-known that maximum likelihood estimators are asymptotically normal with covariance equal to the inverse Fisher information in smooth, finite dimensional parametric models. Thus they are asymptotically efficient. A similar phenomenon has been observed for certain infinite dimensional parameter spaces. We give a simple proof of efficiency, starting from a theorem on asymptotic normality of infinite dimensional M -estimators. The proof avoids the explicit calculation of the Fisher information. We also address Hadamard differentiability of the corresponding M -functionals.     

Business conditions, shared resources and integrative practices in the supply chain

Integration is one of the important concepts in supply chain management. Both in theoretical and empirical contributions, it is shown that integrative practices improve supply chain performance. Our knowledge with respect to which integrative practices are appropriate under different circumstances is limited. This paper develops propositions regarding the influence of business conditions and the type of resources on integrative practices in links between buyers and suppliers. We will study nine business units and the relationship with their key buyers. For each unit, we will investigate the business conditions, the employment of resources for key buyers and the type and level of integrative practices. Higher complexity in business conditions requires higher levels of integration (specifically in the areas of planning and organisation), which are stimulated by buyer-focused resources and restricted by shared resources. In case of lower complexity, we find lower levels of integrative practices. Here, the influence of shared resources on integration is limited.     

Applications of calendar instruments in social surveys: a review

Retrospective reports in survey interviews and questionnaires are subject to many types of recall error, which affect completeness, consistency, and dating accuracy. Concerns about this problem have led to the development of so-called calendar instruments, or timeline techniques. These aided recall procedures have been designed to help respondents gain better access to long-term memory by providing a graphical time frame in which life history information can be represented. In order to obtain more insights into the potential benefits of calendar methodology, this paper presents a review of the application of calendar instruments, their design characteristics and effects on data quality. Calendar techniques are currently used in a variety of fields, including life course research, epidemiology and family planning studies. Despite the growing interest in these new methods, their application often lacks sufficient theoretical foundation and little attention has been paid to their effectiveness. Several recent studies however, have demonstrated that in comparison to more traditional survey methods, calendar techniques can improve some aspects of data quality. While calendar instruments have been shown to be potentially beneficial to retrospective data quality, there is an apparent need for methodological research that generates more systematic knowledge about their application in social surveys.     

Facets of operational performance in an emergency room (ER)

This paper, using detailed time measurements of patients complemented by interviews with hospital management and staff, examines three facets of an emergency room’s (ER) operational performance: (1) effectiveness of the triage system in rationing patient treatment; (2) factors influencing ER’s operational performance in general and the trade-offs in flow times, inventory levels (that is the number of patients waiting in the system), and resource utilization; (3) the impacts of potential process and staffing changes to improve the ER’s performance. Specifically, the paper discusses four proposals for streamlining the patient flow: establishing designated tracks (“fast track,” “diagnostic track”), creating a “holding” area for certain type of patients, introducing a protocol that would reduce the load on physicians by allowing a registered nurse to order testing and treatment for some patients, and potentially and in the longer term, moving from non-ER specialist physicians to ER specialists. The paper’s findings are based on analyzing the paths and flow times of close to two thousand patients in the emergency room of the Medical Center of Leeuwarden (MCL), The Netherlands. Using exploratory data analysis the paper presents generalizable findings about the impacts of various factors on ER’s lead-time performance and shows how the proposals fit with well-documented process improvement theories.     

Estimating the causal effect of a time-varying treatment on time-to-event using structural nested failure time models

In this paper we review an approach to estimating the causal effect of a time-varying treatment on time to some event of interest. This approach is designed for a situation where the treatment may have been repeatedly adapted to patient characteristics, which themselves may also be time-dependent. In this situation the effect of the treatment cannot simply be estimated by conditioning on the patient characteristics, as these may themselves be indicators of the treatment effect. This so-called time-dependent confounding is typical in observational studies. We discuss a new class of failure time models, structural nested failure time models, which can be used to estimate the causal effect of a time-varying treatment, and present methods for estimating and testing the parameters of these models.     

Asymptotic linearity of minimax estimators

The celebrated local asymptotic minimax (LAM) theorem due to HÁjek (1972) also includes the statement that a LAM estimator Is necessarily asymptotically linear. A similar result. is true for semi-parametric models, but Hájek's result doesn't apply to this case as the efficient influence function is often not contained in the (proper) tangent space. This note gives a simple, elementary proof of both the LAM theorem and the necessity of asymptotic linearity of a LAM estimator sequence.