Signal detection models as contextual bandits.

Signal detection theory (SDT) has been widely applied to identify the optimal discriminative decisions of receivers under uncertainty. However, the approach assumes that decision-makers immediately adopt the appropriate acceptance threshold, even though the optimal response must often be learned. Here we recast the classical normal-normal (and power-law) signal detection model as a contextual multi-armed bandit (CMAB). Thus, rather than starting with complete information, decision-makers must infer how the magnitude of a continuous cue is related to the probability that a signaller is desirable, while simultaneously seeking to exploit the information they acquire. We explain how various CMAB heuristics resolve the trade-off between better estimating the underlying relationship and exploiting it. Next, we determined how naive human volunteers resolve signal detection problems with a continuous cue. As anticipated, a model of choice (accept/reject) that assumed volunteers immediately adopted the SDT-predicted acceptance threshold did not predict volunteer behaviour well. The Softmax rule for solving CMABs, with choices based on a logistic function of the expected payoffs, best explained the decisions of our volunteers but a simple midpoint algorithm also predicted decisions well under some conditions. CMABs offer principled parametric solutions to solving many classical SDT problems when decision-makers start with incomplete information.

A lack of repeatability creates the illusion of a trade-off between basal and plastic cold tolerance.

The thermotolerance-plasticity trade-off hypothesis predicts that ectotherms with greater basal thermal tolerance have a lower acclimation capacity. This hypothesis has been tested at both high and low temperatures but the results often conflict. If basal tolerance constrains plasticity (e.g. through shared mechanisms that create physiological constraints), it should be evident at the level of the individual, provided the trait measured is repeatable. Here, we used chill-coma onset temperature and chill-coma recovery time (CCO and CCRT; non-lethal thermal limits) to quantify cold tolerance of Drosophila melanogaster across two trials (pre- and post-acclimation). Cold acclimation improved cold tolerance, as expected, but individual measurements of CCO and CCRT in non-acclimated flies were not (or only slightly) repeatable. Surprisingly, however, there was still a strong correlation between basal tolerance and plasticity in cold-acclimated flies. We argue that this relationship is a statistical artefact (specifically, a manifestation of regression to the mean; RTM) and does not reflect a true trade-off or physiological constraint. Thermal tolerance trade-off patterns in previous studies that used similar methodology are thus likely to be impacted by RTM. Moving forward, controlling and/or correcting for RTM effects is critical to determining whether such a trade-off or physiological constraint exists.

Characteristics of Kenyan women in a prospective cohort study who continue using subdermal contraceptive implants at 12 months.

OBJECTIVE: Subdermal contraceptive implant continuation has not been well studied in Africa. We conducted a secondary data analysis to compare baseline characteristics of Kenyan women who continued to use the subdermal implant at 12 months to those who did not. STUDY DESIGN: Kenyan women aged 18-24 years who presented to a family planning clinic for short-acting hormonal contraception were offered a two-rod subdermal implant instead. Participants were followed for 12 months after initiation of their contraceptive method. Statistical analysis included Pearson's chi-square or Fisher's exact tests for comparisons of proportions. Risk ratios (RRs) and 95% confidence intervals (CIs) were calculated to determine factors associated with continuation. RESULTS: Eighty-six (89%) of the 97 women who chose the implant were followed for 12 months. Of these women, 68 (79%) continued to use the implant. None of the factors we examined had a statistically significant association with continued use of the implant. Duration of intended use was the only strong factor; 83% of women with 3+ years of need continued using the implant, compared to 56% of those with shorter needs (Risk ratio = 1.48, 95% CI = 0.94-2.31). No substantive continuation differences were found when comparing other participant characteristics including months with their current partner, personal desire and partner preference for future children, previous use of modern birth control and other factors. CONCLUSION: High implant continuation rates were noted regardless of previous use of modern birth control, partner preference for children or baseline concern for menstrual change. IMPLICATIONS: Contraceptive use in Africa continues to focus on short-acting contraceptives despite the proven superior efficacy of long-acting reversible contraceptives in other settings. The high subdermal implant continuation among Kenyan women in this prospective study, regardless of baseline characteristics, supports the need for increasing access and future research in this population.

Antepartum evaluation of the fetus and fetal well being.

Despite widespread use of many methods of antenatal testing, limited evidence exists to demonstrate effectiveness at improving perinatal outcomes. An exception is the use of Doppler ultrasound in monitoring high-risk pregnancies thought to be at risk of placental insufficiency. Otherwise, obstetricians should proceed with caution and approach the initiation of a testing protocol by obtaining an informed consent. When confronted with an abnormal test, clinicians should evaluate with a second antenatal test and consider administering betamethasone, performing amniocentesis to assess lung maturity, and/or repeating testing to minimize the chance of iatrogenic prematurity in case of a healthy fetus.

Feasibility of postpartum placement of the levonorgestrel intrauterine system more than 6 h after vaginal birth.

BACKGROUND: The objective of this study was to determine the feasibility of postpartum levonorgestrel intrauterine system (LNG-IUS) placement on the postpartum ward. STUDY DESIGN: This case-series study took place in a teaching hospital in North Carolina. Women were followed for 6 months, and data on method satisfaction, study design satisfaction and expulsion were collected. Descriptive statistics were used. RESULTS: Forty women enrolled. Twenty-nine women (73%) received the LNG-IUS at a median of 20 h (range 7-48 h) after delivery, and all reported that they would recommend this method of contraception to a friend. Eleven women had a spontaneous expulsion (38%; 95% confidence interval 21, 58). CONCLUSION: Placement of LNG-IUS more than 6 h postpartum was acceptable to women in this study. The expulsion rate of 38% had statistical instability and should be interpreted with caution. However, our report may assist with individual counseling of women interested in postpartum LNG-IUS placement, or in future study designs.

Baseline colposcopic findings in women entering studies on female vaginal products.

BACKGROUND: Colposcopy is commonly used for genital tract assessment in safety studies on female-controlled vaginal products. However, findings that are considered "lesions" are present even without product use. We sought to categorize the type and frequency of lesions found on baseline colposcopy evaluation in healthy women to describe natural lower genital tract changes due to environmental factors. STUDY DESIGN: We reviewed demographic information and baseline colposcopic examination findings from subjects in 13 studies of vaginal products. All studies included an aim of identifying colposcopic changes as a means of monitoring safety of a vaginal product or device. Colposcopic evaluations were performed according to the WHO/CONRAD Manual for the Standardization of Colposcopy for the Evaluation of Vaginal Products. RESULTS: A total of 317 lesions were found on 569 baseline colposcopy evaluations, with 192 women (34%) having at least one lesion. The most commonly identified lesions were petechiae and erythema, accounting for 45% and 37% of lesions, respectively. Seventy-three percent of lesions were located on the cervix, whereas 15% of lesions were located on the vaginal wall or fornix. CONCLUSIONS: Lower genital tract colposcopic findings are common in healthy women. Such findings likely represent normal physiologic changes. Future research needs to address whether routine colposcopic examination is necessary in the evaluation of new vaginal products.