W Knoppert | PubMed Health

PubMed1990

Mental arithmetic: effects of calculation procedure and problem difficulty on solution latency.

In this chronometric study of mental arithmetic, problems with sums greater than 20 and less than 100 were presented to third-grade subjects (age 8-9). It is argued that such problems are calculated by using procedures in which the problem is broken down into subproblems for which solutions are retrieved from a declarative knowledge base. Important bottlenecks in this process are the processing capacity (since only one subproblem can be handled at a time) and the storage capacity of working memory (since the original problem and all outcomes of subproblems have to be retained). Therefore it can be hypothesized that arithmetic procedures and types of problems that necessitate more subproblems will lead to longer solution times. Both hypotheses were confirmed. Significant interactions between types of problems and arithmetic procedures show an increasing difference in solution time between the procedures with increasing problem difficulty. It can be concluded that for the type of problems studied, arithmetic procedures requiring a smaller number of subproblems lead to better performance.

Child↗

PubMedDate not supplied

Pneumococcal bacteremia in adults over a 10-year period at University Hospital, Leiden.

The medical records on all cases of pneumococcal bacteremia in adults at the University Hospital, Leiden, over a 10-year period (1976-1986) were retrospectively reviewed. In this series of 147 episodes (an annual incidence of 0.8 episodes/10,000 adults), overall mortality was 25.9%. Factors significantly related to a higher mortality rate were shock, respiratory insufficiency, preexisting renal failure, and rapidly fatal underlying disease. Several laboratory abnormalities-such as a low percentage of band forms, an elevated level of serum lactate dehydrogenase, and hyperbilirubinemia-were significantly related to a poor outcome. Multilobar pneumonia and meningitis were both associated with high mortality, although not to a statistically significant degree. Discriminant analysis showed the presence of shock as the most powerful predictive factor of death. Surprisingly, prior splenectomy did not correlate with higher mortality. Treatment with beta-lactam antibiotics favorably influenced the outcome of illness in patients with ultimately fatal and nonfatal underlying disease, while the use of these agents in patients with rapidly fatal underlying disease did not correlate significantly with a good prognosis.

Adolescent↗