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This study develops a theoretical model for the costs of an exam as a function of its duration. Two kind of costs are distinguished: (1) the costs of measurement errors and (2) the costs of the measurement. Both costs are expressed in time of the student. Based on a classical test theory model, enriched with assumptions on the context, the costs of the exam can be expressed as a function of various parameters, including the duration of the exam. It is shown that these costs can be minimized in time. Applied in a real example with reliability 0.80, the outcome is that the optimal exam time would be much shorter and would have reliability 0.675. The consequences of the model are investigated and discussed. One of the consequences is that optimal exam duration depends on the study load of the course, all other things being equal. It is argued that it is worthwhile to investigate empirically how much time students spend on preparing for resits. Six variants of the model are distinguished, which differ in their weights of the errors and in the way grades affect how much time students study for the resit.

Latent variable models for an infinite sequence (or universe) of manifest variables that may be discrete, continuous, or a combination of both, are considered. A main theorem is presented that characterizes when it is possible to construct latent variable models that satisfy unidimensionality, monotonicity, conditional independence, and tail measurability. (SLD)

In this article, we introduce a novel procedure for improving power of multiple testing procedures (MTPs) of interval hypotheses. When testing interval hypotheses the null hypothesis $P$-values tend to be stochastically larger than standard uniform if the true parameter is in the interior of the null hypothesis. The new procedure starts with a set of $P$-values and discards those with values above a certain pre-selected threshold, while the rest are corrected (scaled-up) by the value of the threshold. Subsequently, a chosen family-wise error rate (FWER) or false discovery rate MTP is applied to the set of corrected $P$-values only. We prove the general validity of this procedure under independence of $P$-values, and for the special case of the Bonferroni method, we formulate several sufficient conditions for the control of the FWER. It is demonstrated that this "filtering" of $P$-values can yield considerable gains of power. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this pilot study was to compare the clinical outcome of initial periodontal scaling and root planing alone (SRP) or SRP combined with Neodynium Yttrium-Aluminum-Garnet (Nd:YAG) laser therapy (NLT) to the same protocol with the use of systemic antimicrobial drugs. Materials and Methods: This double-blind split-mouth design study involved 15 otherwise healthy patients suffering from generalized chronic periodontitis. The subjects were randomly assigned to the two treatment groups. 1. Ultrasonic and hand supra- and sub-gingival scaling with root planing (SRP) on the right side (quardrants 1 and 4). NLT on the left side (quadrants 2 and 3) without the use of antimicrobial drugs as an adjunctive therapy. 2. SRP on the right side (quadrants 1 and 4). NLT on the left side (quadrants 2 and 3) with adjunctive antimicrobial therapy. The clinical parameters recorded during this study were the bleeding on probing index (BPI), periodontal probing depth (PPD), and the presence of the microbes Actinobacillus actinomycetemcomitans (AA), Porphyromonas gingivalis (PG), Bacteroides forsythus (BF), and Treponema denticola (TD). Clinical measurements and microbiological assessments were taken at baseline and after completion of treatment. The clinical protocol of the periodontal treatment includes microbiological assessment, SRP, polishing, and additional NLT for quadrants 2 and 3. All subjects received hygienic instructions and a 0.05% chlorhexidine rinse twice a day. The subjects received amoxicillin, metronidazol, or a combination depending on the outcome of the bacterial testing. The control group received a placebo. Results: The present study demonstrated a significant reduction in mean total counts of the microorganisms AA and BF in the subgingival microbiota following the different test therapies. There tended to be a beneficial effect of the additional use of the Nd:YAG laser, where medication did not have this effect at 90 days. Conclusion: This tendency could encourage clinicians to use the Nd:YAG laser as an adjunctive therapy and abandon the use of antimicrobial agents that increase the risk for antibiotic resistance. [ABSTRACT FROM AUTHOR]