Δοκίμια στη σύγχρονη θεωρία χαρτοφυλακίου και τη λήψη αποφάσεων υπό καθεστώς κινδύνου

Two fundamental questions of particular concern to the economists are: (i) how an economic unit (decision maker or investor) makes its decisions, and (ii) the "risk" tolerance that the economic unit has. In 1944, Von Neumann - Morgenstern founded the Theory of Decision Making under Risk. This theory studies how an economic unit chooses between different lotteries (random variables). In contrast to Decision Making under uncertainty, under "risk" an economic unit knows the objective probabilities of the lotteries. This means that every economic unit faces the same odds and there is no disagreement between the economic units about how likely each lottery event is. Thus, the uncertainty in this context is objectively calculable and is therefore called "risk". The main assumption that the objective probabilities of lotteries are known leads to the Von Neumann - Morgenstern Representation Theorem. The Theorem proves that under "risk", every rational economic unit wishes to maximize its expected utility. However, the utilization of this Theorem, as it stands, presupposes the exact knowledge of the utility function. The various Stochastic Dominance Criteria, as defined in the framework of the Representation Theorem, circumvent this obstacle. They do this by each time setting a rule between the cumulative distributions of two lotteries which should be used by a particular set of investors wishing to maximize their expected utility. A product of the Von Neumann - Morgenstern Representation Theorem is the Modern Portfolio Theory, which was founded by Markowitz in 1952. The main feature of this Theory is that under specific assumptions, the utility function of an investor depends exclusively on the mean and the variance a lottery. This means that the Criterion used by a risk-averse investor who wishes to maximize his expected utility relies solely on the relationships between the means and variances of two lotteries. Once the appropriate Decision Criterion has been identified for a decision maker, the next step is to study his degree of "risk" aversion. In this regard, Arrow - Pratt (1964,1965) define measures of the degree of absolute and relative risk aversion of an investor. These measures essentially study how a decision maker's degree of risk aversion changes with respect to different levels of wealth. The purpose of this doctoral thesis is divided into three parts. First, to examine and evaluate the various theoretical and empirical findings arising from already existing research works in the framework of the Modern Portfolio Theory and more generally of the Theory of Decision Making under Risk. Then, to answer important questions that either the literature has ignored, or the answers given to them are in doubt. And finally, to propose some new methods which contribute to the study and interpretation of the behavior of investors under risk.Δύο θεμελιώδη ερωτήματα τα οποία απασχολούν ιδιαίτερα τους οικονομολόγους είναι: (i) ο τρόπος που μία οικονομική μονάδα (λήπτης αποφάσεων ή επενδυτής) λαμβάνει τις αποφάσεις της, και (ii) η ανοχή που έχει η οικονομική μονάδα στον "κίνδυνο" ("ρίσκο"). Το 1944 οι Von Neumann - Morgenstern θεμελίωσαν τη Θεωρία Λήψης Αποφάσεων υπό καθεστώς ρίσκου. Η Θεωρία αυτή μελετά τον τρόπο με τον οποίο μία οικονομική μονάδα επιλέγει μεταξύ διαφορετικών λοταριών (τυχαίων μεταβλητών). Σε αντίθεση με το καθεστώς αβεβαιότητας, σε καθεστώς ρίσκου μία οικονομική μονάδα γνωρίζει τις αντικειμενικές πιθανότητες των λοταριών. Αυτό σημαίνει ότι κάθε οικονομική μονάδα αντιμετωπίζει τις ίδιες πιθανότητες και δεν υπάρχει διαφωνία μεταξύ των οικονομικών μονάδων για το πόσο πιθανό είναι το κάθε ενδεχόμενο μιας λοταρίας. Συνεπώς, η αβεβαιότητα στο πλαίσιο αυτό είναι αντικειμενικά υπολογίσιμη και ως εκ τούτου ονομάζεται "ρίσκο". Η βασική υπόθεση ότι οι αντικειμενικές πιθανότητες των λοταριών είναι γνωστές, οδηγεί στο Θεώρημα Αναπαράστασης των Von Neumann - Morgenstern. Το Θεώρημα αποδεικνύει ότι σε καθεστώς ρίσκου, κάθε ορθολογική οικονομική μονάδα επιθυμεί να μεγιστοποιήσει την αναμενόμενη χρησιμότητά της. Ωστόσο, η αξιοποίηση του Θεωρήματος αυτού, ως έχει, προϋποθέτει την ακριβή γνώση της συνάρτησης χρησιμότητας. Τα διάφορα Κριτήρια Στοχαστικής Κυριαρχίας, όπως ορίζονται στο πλαίσιο του Θεωρήματος Αναπαράστασης, παρακάμπτουν το εμπόδιο αυτό. Αυτό το καταφέρνουν θέτοντας κάθε φορά έναν κανόνα μεταξύ των αθροιστικών κατανομών δύο λοταριών, τον οποίο θα πρέπει να χρησιμοποιεί ένα συγκεκριμένο σύνολο επενδυτών που επιθυμεί να μεγιστοποιήσει την αναμενόμενη χρησιμότητά του. Προϊόν του Θεωρήματος Αναπαράστασης των Von Neumann - Morgenstern αποτελεί και η Σύγχρονη Θεωρία Χαρτοφυλακίου, την οποία θεμελίωσε ο Markowitz το 1952. Το βασικό χαρακτηριστικό της Θεωρίας αυτής είναι ότι κάτω από συγκεκριμένες υποθέσεις, η συνάρτηση χρησιμότητας ενός επενδυτή εξαρτάται αποκλειστικά από τον μέσο και τη διακύμανση μιας λοταρίας. Αυτό σημαίνει ότι το Κριτήριο το οποίο χρησιμοποιεί ένας επενδυτής που αποστρέφεται τον κίνδυνο και παράλληλα επιθυμεί να μεγιστοποιήσει την αναμενόμενη χρησιμότητά του, στηρίζεται αποκλειστικά στις σχέσεις μεταξύ των μέσων και των διακυμάνσεων δύο λοταριών. Εφόσον έχει προσδιοριστεί το κατάλληλο Κριτήριο Επιλογής για έναν λήπτη αποφάσεων, το επόμενο βήμα είναι να μελετηθεί ο βαθμός αποστροφής του στον "κινδυνο". Ως προς αυτό, οι Arrow - Pratt (1964,1965) ορίζουν τα μέτρα του βαθμού απόλυτης και σχετικής αποστροφής κινδύνου ενός επενδυτή. Τα μέτρα αυτά μελετούν στην ουσία το πώς μεταβάλλεται ο βαθμός αποστροφής κινδύνου ενός λήπτη αποφάσεων για διαφορετικά επίπεδα του πλούτου του. Ο σκοπός της παρούσας διδακτορικής διατριβής χωρίζεται σε τρία μέρη. Αρχικά, να εξετάσει και να αξιολογήσει τα διάφορα θεωρητικά και εμπειρικά ευρήματα που προκύπτουν από ήδη υπάρχουσες ερευνητικές εργασίες στα πλάισια της Σύγχρονης Θεωρίας Χαρτοφυλακίου και γενικότερα της Θεωρίας Λήψης Αποφάσεων υπό καθεστώς ρίσκου. Έπειτα, να απαντήσει σε σημαντικά ερωτήματα τα οποία είτε η βιβλιογραφία έχει αγνοήσει, είτε οι απαντήσεις που έχουν δοθεί σε αυτά τίθενται υπό αμφισβήτηση. Και τέλος, να προτείνει ορισμένες νέες μεθόδους οι οποίες συνεισφέρουν στην μελέτη και ερμηνεία της συμπεριφοράς των επενδυτών σε καθεστώς ρίσκου

Treatment of endometriosis: a review with comparison of 8 guidelines

Background: Endometriosis, the presence of endometrial-like tissue outside the uterus, is a common clinical entity between women of reproductive age, with a prevalence of about 10%. Due to the variety of endometriosis-associated symptoms, a great variety of treatments have been implemented. The aim of this review is to give an overview on therapeutical approaches of eight national and international widely used guidelines. Methods: Six national (College National des Gynecologues et Obstetriciens Francais, National German Guideline (S2k), Society of Obstetricians and Gynaecologists of Canada, American College of Obstetricians (ACOG) and Gynecologists, American Society for Reproductive Medicine (ASRM) and National Institute for Health and Care (NICE) and two international (World Endometriosis Society, European Society of Human Reproduction and Embryology) guidelines are included in this review. Conclusion: All the above-mentioned guidelines agree that the combined oral contraceptive pill, progestogens are therapies recommended for endometriosis associated pain. Concerning infertility, there is no clear consensus about surgical treatment. Discrepancies are also found on recommendation of the second- and third-line treatments. Keywords: Conservative treatment; Endometriosis; Guidelines; Infertility; Pain; Surgical treatment

Treatment of endometriosis: a review with comparison of 8 guidelines

Abstract Background Endometriosis, the presence of endometrial-like tissue outside the uterus, is a common clinical entity between women of reproductive age, with a prevalence of about 10%. Due to the variety of endometriosis-associated symptoms, a great variety of treatments have been implemented. The aim of this review is to give an overview on therapeutical approaches of eight national and international widely used guidelines. Methods Six national (College National des Gynecologues et Obstetriciens Francais, National German Guideline (S2k), Society of Obstetricians and Gynaecologists of Canada, American College of Obstetricians (ACOG) and Gynecologists, American Society for Reproductive Medicine (ASRM) and National Institute for Health and Care (NICE) and two international (World Endometriosis Society, European Society of Human Reproduction and Embryology) guidelines are included in this review. Conclusion All the above-mentioned guidelines agree that the combined oral contraceptive pill, progestogens are therapies recommended for endometriosis associated pain. Concerning infertility, there is no clear consensus about surgical treatment. Discrepancies are also found on recommendation of the second- and third-line treatments. </jats:sec

Leptin concentrations in endometriosis: A systematic review and meta-analysis

Introduction: Endometriosis is an inflammatory condition, affecting mainly women of reproductive age. Leptin is a regulator of food intake and energy expenditure, posing pleiotropic actions, and regulating immunity and fertility. The aim of this study was to systematically review the literature regarding leptin concentrations in biological fluids and tissues of women with endometriosis, and to investigate and propose a possible role of leptin in the pathophysiology of endometriosis. Materials and methods: A systematic search of the literature was conducted in two electronic databases (MEDLINE, COCHRANE) and grey literature for original research articles on humans, published in any language. Results: Twenty-nine studies with 1291 women with endometriosis and 1664 controls were included in the systematic review. Peritoneal fluid and follicular fluid leptin concentrations were higher in endometriosis compared with control group [mean difference (MD) 7.10, 95 % confidence interval (CI) 4.76 to 9.44 ng/mL, 18 studies), (MD 1.35, 95 % CI 0.54-2.17 ng/ml, 2 studies) respectively. No differences were evident in serum (MD 0.92, 95 % CI -0.84 to 2.68 ng/mL, 12 studies) or plasma (MD -0.95, 95 % CI -4.63 to 2.72 ng/mL, 3 studies) between the groups. No meta-analysis was conducted for ovarian tissue leptin (2 studies). Conclusions: This meta-analysis provided evidence for increased leptin concentrations in both peritoneal fluid and follicular fluid of women with endometriosis compared with control; these differences were not present in the serum or plasma. The above results support a potential pathophysiologic role for leptin in the local microenvironment while declines its use as a blood diagnostic marker. Furthermore, we propose a possible role of leptin in the pathophysiology of endometriosis. Keywords: Adiponectin; Endometrioma; Endometriosis; Follicular fluid; Leptin; Leptin receptor; Leptin-binding protein; Peritoneal fluid; Plasma; Serum

Co-Existence of Endometriosis with Ovarian Dermoid Cysts: A Retrospective Cohort Study

Both endometriosis and ovarian dermoid cysts are benign conditions characterized by the presence of well-differentiated tissues in ectopic locations. The presence and surgical excision of these entities can potentially impact ovarian reserves, contributing to reduced chances of future pregnancy. The objective of our study is to investigate the bidirectional association between endometriosis and ovarian dermoid cysts, as well as to analyze the clinical characteristics of patients diagnosed with both conditions. A retrospective cohort study was conducted, including women who underwent laparoscopy and received histological diagnoses of endometriosis and/or dermoid cysts between 2011 and 2019 at the Cantonal Hospital of Schaffhausen. We identified 985 women with endometriosis and 83 women with ovarian dermoid cysts. Among these groups, 22 women presented with both endometriosis and ovarian dermoid cysts. The majority of the above patients had endometriosis stage rASRM I-II (72.7%), with peritoneal endometriosis being the most common phenotype of endometriosis (77.2%). Out of the 14 patients with a desire for future pregnancy, the majority (11/14, 78.5%) had an EFI score of 7&ndash;8. The prevalence of bilateral ovarian dermoid cysts was higher in women with both ovarian dermoid cysts and endometriosis in comparison to women with ovarian dermoid cysts without endometriosis (18% vs. 6.5%). Our study revealed that 26.5% of women with ovarian dermoid cysts also had endometriosis, a notably higher prevalence than observed in the general population. Clinicians should be aware of this co-existence, and preoperative counseling should be an integral part of the care plan for affected individuals, where the potential risks and the available options for fertility preservation should be discussed in detail

Opioid substitution therapy: lowering the treatment thresholds

Background: Opioid substitution therapy (OST) has been established as the gold standard in treating opioid use disorders. Nevertheless, there is still a debate regarding the qualitative characteristics that define the optimal OST intervention, namely the treatment threshold. The aim of this review is twofold: first, to provide a summary and definition of “treatment thresholds”, and second, to outline these thresholds and describe how they related to low and high threshold treatment characteristics and outcomes. Method: We searched the main databases of Medline, PubMed, PsycInfo, EMBASE, CINAHL and the Cochrane Library. Original published research papers, reviews, and meta-analyses, containing the eligible keywords: “opioid substitution”, “OST”, “low threshold”, “high threshold” were searched alone and in combination, up to June, 2015. Results: Treatment thresholds were defined as barriers a patient may face prior to and during treatment. The variables of these barriers were classified into treatment accessibility barriers and treatment design barriers. There are increasing numbers of studies implementing low threshold designs with an increasing body of evidence suggesting better treatment outcomes compared to high threshold designs. Conclusion: Clinical characteristics of low threshold treatments that were identified to increase the effectiveness of OST intervention include increasing accessibility so as to avoid waiting lists, using personalized treatment options regarding medication choice and dose titration, flexible treatment duration, a treatment design that focuses on maintenance and harm reduction with emphasis on the retention of low adherence patients