Model-based evaluation of HIV prevention interventions

The ultimate goal of HIV prevention interventions is to reduce the spread of HIV; however, the effectiveness of these programs is seldom assessed directly. Although direct measurement of an intervention's impact via HIV seroincidence monitoring is usually unfeasible, mathematical models can be used to estimate the number of infections averted by the intervention. This article describes three model-based summary measures of sexually transmitted HIV risk and discusses their relevance to HIV program evaluation in general economic efficiency analyses in particular. The calculation of these measures is demonstrated with an illustrative application to previously published data from an HIV prevention intervention for gay men.     

When is an HIV infection prevented and when is it merely delayed?

HIV prevention programs are typically evaluated using behavioral outcomes. Mathematical models of HIV transmission can be used to translate these behavioral outcomes into estimates of the number of HIV infections averted. Usually, intervention effectiveness is evaluated over a brief assessment period and an infection is considered to be prevented if it does not occur during this period. This approach may overestimate intervention effectiveness if participants continue to engage in risk behaviors. Conversely, this strategy underestimates the true impact of interventions by assuming that behavioral changes persist only until the end of the intervention assessment period. In this article, the authors (a) suggest a simple framework for distinguishing between HIV infections that are truly prevented and those that are merely delayed, (b) illustrate how these outcomes can be estimated, (c) discuss strategies for extrapolating intervention effects beyond the assessment period, and (d) highlight the implications of these findings for HIV prevention decision making.     

Productivity drift in extended learning curves

The pattern of changes in the Extended Learning Curves representing the performance of 114 assembly workers in an electronics firm is examined in terms of changes in productivity drift over long periods of time. It is shown that 2 types of discontinuities can occur. The first consists of a temporary levelling off in productivity followed by a recovery to new higher levels of productivity; the second has a sustained period of negative productivity drift. A number of work facets are statistically tested as possible causes of these patterns of productivity drift, but, the only significant relationship (at P ≤ 0.05 level) is with length of service in job. Some evidence is presented to show that conventional work measurement methods are not effective in terms of assessing the true work output of experienced workers since such workers are able to beat the system by claiming those allowances which are most difficult to cross-check.     

Cooperation in the Face of Conflict: Effects of Top Managers’ Trust Beliefs in their Firms’ Major Suppliers

As with any relationships, those between buying firms and their major suppliers are likely to experience situations of conflict. When facing such situations, top managers tend to approach conflict either cooperatively or competitively. However, when and why top managers tend towards cooperation or competition is far from clear. This study proposes a novel link between the theory of cooperation and competition and the discounting principle of attribution theory to argue that it is top managers’ trust beliefs in their firms’ major suppliers that influences their intended approach to conflict. Using survey data from 140 C‐level managers and business owners, the authors develop and test a model that differentiates between two attributional dimensions of trust (competence and goodwill) and the specific relational conditions that influence how these attributions operate. The results indicate that top managers’ trust in their suppliers’ competence and goodwill is, in fact, decisive in determining how they intend to approach conflict. Further, the authors demonstrate that a top manager's trust belief in the supplier's goodwill is of particular relevance in driving the top manager to cooperate in the face of conflict. However, this link seems to be contingent on the specific conditions of the buyer–supplier relationship in question.     

A production engineering approach to robot selection

The successful introduction of robots into an industrial enterprise means real commitment, engineering support, and detailed involvement in the planning of an integrated manufacturing system. In particular, the production engineer is clearly seen in this context to be the system designer. He must therefore be in a position to specify the performance of all man and machine components within the system such that productivity is maximised. Robot types are reviewed, and analogies between man and machine are used to introduce the RTM concept. Finally, a simple method is given for estimating robot throughput times from elementary velocity profiles. The fall-off in throughput due to the effect of many small robot movements is emphasised.     

Stages of sexual readiness and six-month stage progression among African American pre-teens

We examined the range of sexual intentions and behaviors preceding sexual initiation among 211 African-American pre-teens assigned to the control arm of a longitudinal community-based intervention trial. Stage of sexual readiness was assessed using the stage of change construct from the Transtheoretical Model, and patterns of stage movement during a 6-month period were examined. Overall, 90% of participants were in precontemplation at baseline, with the proportion of participants in this stage declining with each year of age. There was substantial stability in stage of sexual readiness during the 6-month period (87% stable). While definitive conclusions regarding exact patterns of movement are not yet possible, stage movement does not appear to be linear for all pre-teens, and there is evidence of both stage progression and regression. We present emerging patterns of stage movement, which suggest potential variation by age, gender, and baseline stage, and discuss potential implications.