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Monitoring the epidemic of Human Immunodeficiency Virus (HIV) infection plays a vital role in tracking the leading edge of HIV transmission and designing intervention programs both at individual and population level. At individual level, it is imperative to identify newly infected individuals to reduce onwards transmission. At population level, knowledge on the HIV incidence is essential to monitor the spread of the epidemic and plan/evaluate HIV prevention programs. This dissertation will examine the way in which biomarker data can be used to monitor the HIV epidemic. There are two primary aims of this thesis: a) to investigate the use of biomarkers in quantifying the recency of HIV infection at individual level and b) to estimate quantities such as mean window period and testing rate that are the building blocks for estimating HIV incidence at population level. We apply and further develop existing statistical methods to answer the research questions of interest. At individual level, we investigate the use of one or more biomarkers to quantify the recency of HIV infection. We propose a novel approach to make probabilistic statements on the recency of HIV infection by combining the knowledge on the growth of such biomarkers with observations from a newly diagnosed individual. Univariate and bivariate non-linear mixed-effects models are implemented in a fully Bayesian framework. A simulation study is conducted to investigate the biomarkers’ features that affect the accuracy of the estimation of recency. The research findings suggest that rapidly evolving biomarkers of antibody response, such as LAg Avidity, provide reliable estimates of the probability of recency. The proposed methods are applied to a panel of individuals for whom information on various biomarkers is given along with an estimated date of detectable infection. At population level, we focus on estimating two fundamental ingredients, the mean window period and the HIV testing rate, required for estimating HIV incidence using biomarker data. We compare commonly used statistical methods and explore the use of multi-state models in estimating the mean window period of the fourth generation Architect Avidity. We further investigate the factors that are associated with the probability of having an HIV test and the HIV testing rate using surveillance data. Logistic and count regression models using the Generalized Estimating Equations (GEE) approach are employed to make inference at population level about the probability of testing and HIV testing rate respectively.

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Denna studie syftar till att undersöka om icke-professionella investerare med lite eller ingen utbildning inom ekonomi påverkas av en nysseffekt. För att testa detta utvecklas två rapporter gällande ett fiktivt bolag vars enda skillnad utgörs av ordningen informationen presenteras i. Studenter på Uppsala universitets olika campus får sedan läsa en av rapporterna och svara på hur villiga de är att investera i bolaget. Svaren jämförs för att se om presentationsordningen påverkar hur villiga deltagarna är att investera. Vidare fördelas materialet baserat på utbildning, kön och självrapporterad riskattityd för att se om dessa faktorer påverkar om deltagarna påverkas av en nysseffekt eller ej. Resultatet visar att den enda gruppen som uppvisade en statistiskt signifikant nysseffekt var de deltagare som läste första året på en ekonomikandidat. Samtliga fördelningar resulterade i signifikanta skillnader mellan grupperna.

Salient features of a task play an important role in how people create task representations which then influence strategy selection for accomplishing the task. We examined two theories, Represent-Construct-Choose-Learn and Rational Metareasoning, both of which incorporate task features into their models of strategy selection but differ in feature set modification. We used the Building Sticks Task (BST) in which it has been shown that people are sensitive to a salient feature in the BST to test the predictions of both theories. The results showed that neither theory aligned closely with empirical data. Additionally, we investigated participants’ strategy preferences in BST and explored the potential influence of recent strategy use. Our findings revealed a preference for the undershoot strategy and a recency effect favoring the overshoot strategy. These findings highlight the complex nature of strategy selection and emphasize the significance of considering how task features, strategy preferences, and recency effects interact.

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The role of the primate frontopolar cortex (FPC) has been investigated using human neuroimaging, lesion and disruption techniques. The results of these investigations have led to a variety of theories regarding the function of this region. It has been linked to the formation of task sets, the performance of multiple tasks, reasoning, context-specific memory (including episodic memory, prospective memory and source memory), attention to internally or externally generated information, mentalising and decision-making. It has not previously been possible to study this area using animal lesion techniques. Here, behavioural experiments conducted using non-human primates (rhesus macaque monkeys) who have received lesions to the frontal pole investigate the contribution of this region to context-specific memory, decision-making and social cognition. Functional magnetic resonance imaging (fMRI) is used to investigate changes in functional network connectivity which occur after lesions to this region. A long-lasting impairment is observed in contextual memory judgements (specifically, how recently a stimulus was encountered) after lesions to the frontal pole. An analysis of the influence of the outcomes of previous choices on behaviour on an analogue to the Wisconsin Card Sorting Test (WCST) indicate that monkeys with lesions to area 10 may be less influenced by the outcomes of an extended history of rewards than control animals. Long-lasting widespread disruption to functional networks after lesions to this region indicate that indirect anatomical connections from this region to posterior areas play a crucial role in the normal functioning of posterior networks.

Previous research has documented the prevalent effects of message order on message persuasiveness. Based on the Belief Updating Model (Hogarth and Einhorn, 1992), response mode has been found as one moderator of primacy versus recency effects. The present study considers additionally the role of culture as a moderator. Because internalized cultural values and norms affect how messages are processed and interpreted, we propose that cultural differences in cognitive processing styles will impact whether primacy or recency effects are stronger under different message order conditions in for Easterners and Westerners. Results from the current work offer evidence that both culture and cognitive style (holistic versus analytical thinking) serve as moderators to explain message order effects. Results replicate prior studies showing a primacy effect with End of Sequence response mode and a recency effect with Step-by-Step response mode. Further, we found that Easterners were more influenced by the primacy effect when compared to Westerners. However, the effect of primacy was attenuated by response mode. Westerners were equally influenced by both primacy and recency effects.