Optimistic Planning for Markov Decision Processes

International audienceThe reinforcement learning community has recently intensified its interest in online planning methods, due to their relative independence on the state space size. However, tight near-optimality guarantees are not yet available for the general case of stochastic Markov decision processes and closed-loop, state-dependent planning policies. We therefore consider an algorithm related to AO* that optimistically explores a tree representation of the space of closed-loop policies, and we analyze the near-optimality of the action it returns after n tree node expansions. While this optimistic planning requires a finite number of actions and possible next states for each transition, its asymptotic performance does not depend directly on these numbers, but only on the subset of nodes that significantly impact near-optimal policies. We characterize this set by introducing a novel measure of problem complexity, called the near-optimality exponent. Specializing the exponent and performance bound for some interesting classes of MDPs illustrates the algorithm works better when there are fewer near-optimal policies and less uniform transition probabilities

Health anxiety and perceived vulnerability to illness

The purpose of this study was to test several hypotheses suggested by Warwick & Salkovskis's (1990) recently developed cognitive-behavioural theory of hypochondriasis and health anxiety. The main hypothesis of the study was that perceived vulnerability to illness, fear of bodily sensations and changes, and dysfunctional attitudes toward illness are the major components of health anxiety. University students (N=161) completed a questionnaire package with measures of health anxiety (including the Whitely Index), perceived vulnerability to illness, fear of bodily sensations, dysfunctional attitudes, depression (BDI), and trait anxiety (STAI-T). The results suggested that the most important of the hypothesized components was dysfunctional attitudes toward illness, followed by perceived vulnerability toward illness. However, these predictors did not account for a large proportion of the variance in health anxiety scores, and their contribution was further reduced by including depression as a covariate. The results are discussed regarding problems with measurement, sampling, and theory. Further research, especially studies devoted to the role of experience of illness in health anxiety, is suggested.Arts, Faculty ofPsychology, Department ofGraduat

The significance of obsessions

The purpose of this thesis was to investigate a specific cognitive theory of obsessions; namely, that unwanted and repugnant intrusive thoughts cause distress and persist when the person interprets their occurrence as highly personally significant and important. Two studies were conducted. In the first study, we described the development and undertook a validation study of a new scale of obsessional-compulsive symptoms, the Vancouver Obsessional Compulsive Inventory (VOCI). This measure was a necessary first step because established measures of obsessional-compulsive symptoms are inadequate in their assessment of a number of domains of obsessional-compulsive complaints, particularly obsessions. Our findings in samples of people with obsessivecompulsive disorder (OCD), people with other anxiety disorders or depression, community adults, and undergraduate students suggest that the VOCI is a promising new measure. In the second study, we investigated the role of interpretations of the personal significance and importance of intrusive thoughts in the occurrence of obsessions. Specifically, we hypothesized that people who have repugnant obsessions or frequent, distressing intrusive thoughts would interpret their intrusive thoughts as highly personally significant and important. Our hypotheses were, in general, supported. There was a clear relationship between beliefs and interpretations of the importance of thoughts and obsessions in both OCD and nonclinical samples. In addition, these beliefs and appraisals appeared to be specifically related to repugnant obsessions, rather than obsessive-compulsive complaints in general. This research represents one of the first attempts to evaluate the assertion that misinterpretations of intrusive thoughts are fundamental in the experience of obsessions. The development of the VOCI was a necessary first step in evaluating the relationship between interpretations of personal significance and particular obsessional-compulsive complaints. By demonstrating specific interpretations that are associated with clinical obsessions, we hope to refine cognitive-behavioural models of obsessions, and suggest ways in which current cognitive-behaviour therapy for obsessions can be sharpened and made more effective.Arts, Faculty ofPsychology, Department ofGraduat

Correlates and Predictors of New Mothers’ Responses to Postpartum Thoughts of Accidental and Intentional Harm and Obsessive Compulsive Symptoms

Background: Unwanted, intrusive thoughts of infant-related harm are a normal, albeit distressing experience for most new mothers. The occurrence of these thoughts can represent a risk factor for the development of obsessive compulsive disorder (OCD). As the early postpartum period represents a time of increased risk for OCD development, the transition to parenthood provides a unique opportunity to better understand OCD development. Aims: The purpose of this study was to assess components of cognitive behavioural conceptualizations of postpartum OCD in relation to new mothers’ thoughts of infant-related harm. Method: English-speaking pregnant women (n = 100) participated. Questionnaires were completed at approximately 36 weeks of gestation, and at 4 and 12 weeks postpartum. An interview to assess postpartum harm thoughts was administered at 4 and 12 weeks postpartum. Questionnaires assessed OC symptoms, OC-related beliefs, fatigue, sleep difficulties and negative mood. Results: Prenatal OC-related beliefs predicted postpartum OC symptoms, as well as harm thought characteristics and behavioural responses to harm thoughts. The severity of behavioural responses to early postpartum harm thoughts did not predict later postpartum OC symptoms, but did predict frequency and time occupation of accidental harm thoughts, and interference in parenting by intentional harm thoughts. Strong relationships between OC symptoms and harm thought characteristics, and concurrent sleep difficulties, negative mood and fatigue were also found. Conclusions: Findings provide support for cognitive behavioural conceptualizations of postpartum OCD and emphasize the importance of maternal sleep, fatigue and negative mood in the relationship between OC-related beliefs and maternal cognitive and behavioural responses to postpartum harm thoughts.</jats:p

The Mother's Autonomy in Decision Making (MADM) scale: Patient-led development and psychometric testing of a new instrument to evaluate experience of maternity care.

OBJECTIVE:To develop and validate a new instrument that assesses women's autonomy and role in decision making during maternity care. DESIGN:Through a community-based participatory research process, service users designed, content validated, and administered a cross-sectional quantitative survey, including 31 items on the experience of decision-making. SETTING AND PARTICIPANTS:Pregnancy experiences (n = 2514) were reported by 1672 women who saw a single type of primary maternity care provider in British Columbia. They described care by a midwife, family physician or obstetrician during 1, 2 or 3 maternity care cycles. We conducted psychometric testing in three separate samples. MAIN OUTCOME MEASURES:We assessed reliability, item-to-total correlations, and the factor structure of the The Mothers' Autonomy in Decision Making (MADM) scale. We report MADM scores by care provider type, length of prenatal appointments, preferences for role in decision-making, and satisfaction with experience of decision-making. RESULTS:The MADM scale measures a single construct: autonomy in decision-making during maternity care. Cronbach alphas for the scale exceeded 0.90 for all samples and all provider groups. All item-to-total correlations were replicable across three samples and exceeded 0.7. Eigenvalue and scree plots exhibited a clear 90-degree angle, and factor analysis generated a one factor scale. MADM median scores were highest among women who were cared for by midwives, and 10 or more points lower for those who saw physicians. Increased time for prenatal appointments was associated with higher scale scores, and there were significant differences between providers with respect to average time spent in prenatal appointments. Midwifery care was associated with higher MADM scores, even during short prenatal appointments (<15 minutes). Among women who preferred to lead decisions around their care (90.8%), and who were dissatisfied with their experience of decision making, MADM scores were very low (median 14). Women with physician carers were consistently more likely to report dissatisfaction with their involvement in decision making. DISCUSSION:The Mothers Autonomy in Decision Making (MADM) scale is a reliable instrument for assessment of the experience of decision making during maternity care. This new scale was developed and content validated by community members representing various populations of childbearing women in BC including women from vulnerable populations. MADM measures women's ability to lead decision making, whether they are given enough time to consider their options, and whether their choices are respected. Women who experienced midwifery care reported greater autonomy than women under physician care, when engaging in decision-making around maternity care options. Differences in models of care, professional education, regulatory standards, and compensation for prenatal visits between midwives and physicians likely affect the time available for these discussions and prioritization of a shared decision making process. CONCLUSION:The MADM scale reflects person-driven priorities, and reliably assesses interactions with maternity providers related to a person's ability to lead decision-making over the course of maternity care