On Variable Selection of a Nonlinear Non-parametric System with a Limited Data Set: A Stepwise Algorithm

his paper considers a problem of identification for a high dimensional nonlinear non-parametric system when only a limited data set is available. The algorithms are proposed for this purpose which exploit the relationship between the input variables and the output and further the inter-dependence of input variables so that the importance of the input variables can be established. A key to these algorithms is the non-parametric two stage input selection algorithm.

Tooth replacement for partially dentate elders: a willingness-to-pay analysis

Objectives: The primary aim of this study was to investigate partially dentate elders’ willingness-to-pay (WTP) for two different tooth replacement strategies: using Removable Partial Dentures (RPDs) and, functionally orientated treatment (SDA). The secondary aim was to measure the same patient group’s WTP for dental implants. Methods: Patients who had completed a previous RCT comparing two tooth replacement strategies (RPDs and SDA) were recruited. 59 patients were asked to indicate their WTP for treatment to replace missing teeth in a number of hypothetical scenarios using the payment card method of contingency evaluation coupled to different costs. Data were collected on patients’ social class, longest held occupation, income levels and social circumstances. Results: The median age for the patient sample was 72.0 years (IQR: 71-75 years). Patients who had previously been provided with RPDs indicated that their WTP for this treatment strategy was significantly higher than those patients who had received SDA treatment (Mann-Whitney U Test: p<0.001). This group were also WTP a higher price for SDA treatment than those patients who had previously been treated according to this modality (Mann-Whitney U Test: p=0.005). The results indicated that patients’ age was not correlated with WTP but both social class and current income levels were significantly correlated (Spearman’s rank correlation: p<0.05). Patients in both treatment groups exhibited llittle WTP for dental implant treatment with a median price recorded which was lower than either RPD or SDA treatment. Conclusions: Amongst this patient cohort previous treatment experience had a strong influence on WTP as did social class and current income levels. The patients’ WTP indicated that they did not value dental implants over simpler forms of tooth replacement such as RPDs or a SDA approach.

Willingness to pay for cataract surgery in rural Southern China.

PURPOSE: To study willingness to pay for cataract surgery, and its associations, in Southern China. DESIGN: Cross-sectional willingness-to-pay interview incorporating elements of the open-ended and bidding formats. PARTICIPANTS: Three-hundred thirty-nine persons presenting for cataract screening in Yangjiang, China, with presenting visual acuity (VA) < or = 6/60 in either eye due to cataract. METHODS: Subjects underwent measurement of their VA and a willingness-to-pay interview. Age, gender, literacy, education, and annual income also were recorded. MAIN OUTCOME MEASURES: Maximum amount that the subjects would be willing to pay for cataract surgery. RESULTS: Among 325 (95.9%) subjects completing the interview, 169 (52.0%) were 70 years or older, 213 (65.5%) were women, and 217 (66.8%) had an annual income of <5000 renminbi (5000 = US 625 dollars). Eighty percent (n = 257) of participants were willing to pay something for surgery (mean, 442+/-444 renminbi [US 55 dollars+/-55]). In regression models, older subjects were willing to pay less (8 renminbi [US 1 dollar] per year of age; P = 0.01). Blind subjects were significantly more likely (odds ratio, 5.7; 95% confidence interval, 1.7-19.3) to pay anything for surgery, but would pay on average 255 renminbi (US 32 dollars) less (P = 0.004). Persons at the highest annual income level (>10,000 renminbi [US 1250 dollars]) would pay 50 dollars more for surgery than those at the lowest level (<5000 renminbi) (P = 0.0003). The current cost of surgery in this program is 500 renminbi (US 63 dollars). CONCLUSIONS: Sustainable programs will need to attract younger, more well-to-do persons with better vision, while still providing access to the neediest patients.

Willingness to pay for potential enhancements to a low-cost cataract surgical package in rural southern China.

PURPOSE: To assess determinants of patients' willingness to pay (WTP) for potential components of a multi-tiered cataract surgical package offered by a non-governmental organization (NGO) in rural China. DESIGN: Cross-sectional study. METHODS: Demographic and clinical data were collected from 505 patients presenting for cataract screening or surgery in Yangjiang, China. Willingness to pay for potential enhancements to the current surgery package was assessed using a bidding format with random payment cards. RESULTS: Among 426 subjects (84.4%) completing interviews, the mean age was 73.9 ± 7.3 years, 67.6% were women and 73% (n = 310) would pay for at least one offering, with 33-38% WTP for each item. Among those who would pay, the mean WTP for food was US$1.68 ± 0.13, transportation US$3.24 ± 0.25, senior surgeon US$50.0 ± 3.36 and US$89.4 ± 4.19 for an imported intra-ocular lens (IOL). The estimated total recovery from these enhancements under various assumptions would be US$20-50 (compared to the current programme price of US$65). In multivariate models, WTP for the senior surgeon increased with knowledge of a person previously operated for cataract (OR = 2.13, 95% CI 1.42-3.18, p < 0.001). Willingness to pay for the imported IOL increased with knowledge of a previously operated person (OR = 1.85, 95% CI 1.24-2.75, p < 0.01) and decreased with age >75 years (OR = 0.61, 0.40-0.93, p < 0.05). CONCLUSIONS: Opportunities exist to increase cataract programme revenues through multi-tiered offerings in this setting, allowing greater subsidization of low-income patients. Personal familiarity with cataract surgery is important in determining WTP. © 2011 The Authors. Acta Ophthalmologica © 2011 Acta Ophthalmologica Scandinavica Foundation.

Tooth replacement for partially dentate elders: a willingness-to-pay analysis

Objectives: The primary aim of this study was to investigate partially dentate elders’ willingness-to-pay (WTP) for two different tooth replacement strategies: using Removable Partial Dentures (RPDs) and, functionally orientated treatment (SDA). The secondary aim was to measure the same patient group’s WTP for dental implants.Methods: Patients who had completed a previous RCT comparing two tooth replacement strategies (RPDs and SDA) were recruited. 59 patients were asked to indicate their WTP for treatment to replace missing teeth in a number of hypothetical scenarios using the payment card method of contingency evaluation coupled to different costs. Data were collected on patients’ social class, longest held occupation, income levels and social circumstances.Results: The median age for the patient sample was 72.0 years (IQR: 71-75 years). Patients who had previously been provided with RPDs indicated that their WTP for this treatment strategy was significantly higher than those patients who had received SDA treatment (Mann-Whitney U Test: p<0.001). This group were also WTP a higher price for SDA treatment than those patients who had previously been treated according to this modality (Mann-Whitney U Test: p=0.005). The results indicated that patients’ age was not correlated with WTP but both social class and current income levels were significantly correlated (Spearman’s rank correlation: p<0.05).Patients in both treatment groups exhibited llittle WTP for dental implant treatment with a median price recorded which was lower than either RPD or SDA treatment.Conclusions: Amongst this patient cohort previous treatment experience had a strong influence on WTP as did social class and current income levels. The patients’ WTP indicated that they did not value dental implants over simpler forms of tooth replacement such as RPDs or a SDA approach.

Investigating the Implications of a Variable RBE on Proton Dose Fractionation Across a Clinical Pencil Beam Scanned Spread-Out Bragg Peak

Purpose: To investigate the clinical implications of a variable relative biological effectiveness (RBE) on proton dose fractionation. Using acute exposures, the current clinical adoption of a generic, constant cell killing RBE has been shown to underestimate the effect of the sharp increase in linear energy transfer (LET) in the distal regions of the spread-out Bragg peak (SOBP). However, experimental data for the impact of dose fractionation in such scenarios are still limited.

Methods and Materials: Human fibroblasts (AG01522) at 4 key depth positions on a clinical SOBP of maximum energy 219.65 MeV were subjected to various fractionation regimens with an interfraction period of 24 hours at Proton Therapy Center in Prague, Czech Republic. Cell killing RBE variations were measured using standard clonogenic assays and were further validated using Monte Carlo simulations and parameterized using a linear quadratic formalism.

Results: Significant variations in the cell killing RBE for fractionated exposures along the proton dose profile were observed. RBE increased sharply toward the distal position, corresponding to a reduction in cell sparing effectiveness of fractionated proton exposures at higher LET. The effect was more pronounced at smaller doses per fraction. Experimental survival fractions were adequately predicted using a linear quadratic formalism assuming full repair between fractions. Data were also used to validate a parameterized variable RBE model based on linear α parameter response with LET that showed considerable deviations from clinically predicted isoeffective fractionation regimens.

Conclusions: The RBE-weighted absorbed dose calculated using the clinically adopted generic RBE of 1.1 significantly underestimates the biological effective dose from variable RBE, particularly in fractionation regimens with low doses per fraction. Coupled with an increase in effective range in fractionated exposures, our study provides an RBE dataset that can be used by the modeling community for the optimization of fractionated proton therapy.

Towards the 2021 UK Census imputation strategy: Response mode as a matching variable in a donor-based approach?

Since July 2014, the Office for National Statistics has committed to a predominantly online 2021 UK Census. Item-level imputation will play an important role in adjusting the 2021 Census database. Research indicates that the internet may yield cleaner data than paper based capture and attract people with particular characteristics. Here, we provide preliminary results from research directed at understanding how we might manage these features in a 2021 UK Census imputation strategy. Our findings suggest that if using a donor-based imputation method, it may need to consider including response mode as a matching variable in the underlying imputation model.

Willingness to pay for personalised nutrition across Europe

BACKGROUND: Personalised nutrition (PN) may promote public health. PN involves dietary advice based on individual characteristics of end users and can for example be based on lifestyle, blood and/or DNA profiling. Currently, PN is not refunded by most health insurance or health care plans. Improved public health is contingent on individual consumers being willing to pay for the service.

METHODS: A survey with a representative sample from the general population was conducted in eight European countries (N= 8233). Participants reported their willingness to pay (WTP) for PN based on lifestyle information, lifestyle and blood information, and lifestyle and DNA information. WTP was elicited by contingent valuation with the price of a standard, non-PN advice used as reference.

RESULTS: About 30% of participants reported being willing to pay more for PN than for non-PN advice. They were on average prepared to pay about 150% of the reference price of a standard, non-personalised advice, with some differences related to socio-demographic factors.

CONCLUSION: There is a potential market for PN compared to non-PN advice, particularly among men on higher incomes. These findings raise questions to what extent personalized nutrition can be left to the market or should be incorporated into public health programs.

Variable Window Power Spectral Density Attack

Side channel attacks permit the recovery of the secret key held within a cryptographic device. This paper presents a new EM attack in the frequency domain, using a power spectral density analysis that permits the use of variable spectral window widths for each trace of the data set and demonstrates how this attack can therefore overcome both inter-and intra-round random insertion type countermeasures. We also propose a novel re-alignment method exploiting the minimal power markers exhibited by electromagnetic emanations. The technique can be used for the extraction and re-alignment of round data in the time domain.