Andreia Teixeira

Conditional Rényi Entropies

There is no generally accepted definition of conditional Rényi entropy. The (unconditional) Rényi entropy depends on a parameter α, which for the case of min-entropy takes the value ∞. Even for this particular case, there are several proposals for the definition of conditional entropy. This paper describes three general definitions of conditional Rényi entropy that were found or suggested in the literature. Their properties are studied and their values, as a function of α, are compared. The particular case of min-entropy is widely used in cryptography as a security parameter; this case is studied in some detail.

Entropy Measures vs. Kolmogorov Complexity

Kolmogorov complexity and Shannon entropy are conceptually different measures. However, for any recursive probability distribution, the expected value of Kolmogorov complexity equals its Shannon entropy, up to a constant. We study if a similar relationship holds for R´enyi and Tsallis entropies of order α, showing that it only holds for α = 1. Regarding a time-bounded analogue relationship, we show that, for some distributions we have a similar result. We prove that, for universal time-bounded distribution mt(x), Tsallis and Renyi entropies converge if and only if α is greater than 1. We also establish the uniform continuity of these entropies.

Impaired angiogenesis as a feature of digital ulcers in systemic sclerosis

Impaired angiogenesis in systemic sclerosis has a major role in tissue injury pathogenesis. Our objective was to determine whether angiogenic biomarkers (vascular endothelial growth factor (VEGF), endoglin, and endostatin) are related to microvascular damage and to determine their predictive value for new digital ulcers (DU). The main outcome of the study was the occurrence of a new digital ulcer during 3-year follow-up. This prospective longitudinal study was performed between October 2011 and December 2014. Seventy-seven patients definitely diagnosed with systemic sclerosis where divided into two groups: those with active DU at baseline and those with no DU until enrollment. Patients were matched by sex and age with healthy controls. Serum levels of VEGF, endoglin, and endostatin were measured at enrollment, and several nailfold videocapillaroscopies were performed during the 3-year follow-up. Serum levels of VEGF were lower (245.06, 158.68–347.33; p < 0.001) and those of endoglin were higher (3.013, 1.463–7.023; p < 0.001) in patients with active DU than those with no DU history (339.49, 202.00–730.93/1.879, 0.840–3.280), and they were higher than those found in controls (178.030, 101.267–222.102)/0.277, 0.154–0.713), respectively. No differences in endostatin levels were found between groups (p = 0.450). Endoglin was the only biomarker significantly different (p = 0.031) between patients with diffuse versus limited systemic sclerosis and between early, active, and late patterns (p = 0.020). VEGF was identified as an independent predictor for the development of new DU. Our study confirmed the relationship between angiogenic vascular biomarkers and the occurrence of DU. Endoglin and VEGF serum levels are potential risk factors, and VEGF has a predictive value for the occurrence of new DU.

Endothelial dysfunction, microvascular damage and ischemic peripheral vasculopathy in systemic sclerosis

OBJECTIVE To evaluate endothelial dysfunction and microvascular damage in secondary Raynaud Phenomenon (SRP) and Systemic sclerosis (SSc)-associated patients as possible predictors of ischemic fingertip digital ulcers (DU) in a 3-year clinical follow-up. METHODS Flow-mediated dilatation (FMD), nailfold videocapillaroscopy (NVC), endothelin-1 (ET-1) and asymmetric dimethylarginine (ADMA) were analysed in a 3-year observational cohort study of 77 SRP patients with systemic sclerosis. The primary outcome was the occurrence of a new DU. RESULTS Risk factors for DU at baseline were low FMD% (p < 0.001), NVC pattern (p < 0.001), high microangiopathy evolution score (MES) (p < 0.001), increased ET-1 (p < 0.001) and increased ADMA serum levels (p = 0.001). Median time to the occurrence of a new DU was 4.50 (1.25-16.25) months. The risk factors for the occurrence of at least one new DU episode in follow-up included a history of at least one DU before enrolment (p < 0.001), autoantibody anti-scleroderma-70 (p = 0.012), NVC late pattern (p < 0.001), high MES score (p < 0.001), low FMD% (p < 0.001) and increased ET-1 serum levels (p < 0.001).We used univariate Cox regression analysis to show that FMD >9.41% (HR: 0.37 95% CI: 0.14-0.99) and ET-1 >11.85 pmol/L (HR: 3.81 95% CI: 1.41-10.26) and NVC (HR: 2.29 95% CI: 0.97-5.38) were predictors of DU recurrence. In terms of first DU event in naïve DU patients at baseline, late NVC pattern (HR: 12.66 95% CI: 2.06-77.89) and MES score (HR: 1.693 95% CI: 1.257-2.279) were independent predictors. CONCLUSION This study identified endothelium dysfunction biomarkers (FMD and ET-1) and severe microvascular damage in NVC as strong predictors of new DU in SSc patients.

The effect of a test ordering software intervention on the prescription of unnecessary laboratory tests - a randomized controlled trial

BackgroundThe way software for electronic health records and laboratory tests ordering systems are designed may influence physicians’ prescription. A randomised controlled trial was performed to measure the impact of a diagnostic and laboratory tests ordering system software modification.MethodsParticipants were family physicians working and prescribing diagnostic and laboratory tests.The intervention group had a modified software with a basic shortcut menu changes, where some tests were withdrawn or added, and with the implementation of an evidence-based decision support based on United States Preventive Services Task Force (USPSTF) recommendations. This intervention group was compared with usual software (control group).The outcomes were the number of tests prescribed from those: withdrawn from the basic menu; added to the basic menu; marked with green dots (USPSTF’s grade A and B); and marked with red dots (USPSTF’s grade D).ResultsComparing the monthly average number of tests prescribed before and after the software modification, from those tests that were withdrawn from the basic menu, the control group prescribed 33.8 tests per 100 consultations before and 30.8 after (p = 0075); the intervention group prescribed 31.3 before and 13.9 after (p < 0001). Comparing the tests prescribed between both groups during the intervention, from those tests that were withdrawn from the basic menu, the intervention group prescribed a monthly average of 14.0 vs. 29.3 tests per 100 consultations in the control group (p < 0.001). From those tests that are USPSTF’s grade A and B, intervention group prescribed 66.8 vs. 74.1 tests per 100 consultations in the control group (p = 0.070). From those tests categorised as USPSTF grade D, the intervention group prescribed an average of 9.8 vs. 11.8 tests per 100 consultations in the control group (p = 0.003).ConclusionsRemoving unnecessary tests from a quick shortcut menu of the diagnosis and laboratory tests ordering system had a significant impact and reduced unnecessary prescription of tests.The fact that it was not possible to perform the randomization at the family physicians’ level, but only of the computer servers is a limitation of our study. Future research should assess the impact of different tests ordering systems during longer periods.Trial registrationISRCTN45427977, May 1st 2014 (retrospectively registered).

Portuguese Family Physicians’ Awareness of Diagnostic and Laboratory Test Costs: A Cross-Sectional Study

Background Physicians’ ability to make cost-effective decisions has been shown to be affected by their knowledge of health care costs. This study assessed whether Portuguese family physicians are aware of the costs of the most frequently prescribed diagnostic and laboratory tests. Methods A cross-sectional study was conducted in a representative sample of Portuguese family physicians, using computer-assisted telephone interviews for data collection. A Likert scale was used to assess physician’s level of agreement with four statements about health care costs. Family physicians were also asked to estimate the costs of diagnostic and laboratory tests. Each physician’s cost estimate was compared with the true cost and the absolute error was calculated. Results One-quarter (24%; 95% confidence interval: 23%–25%) of all cost estimates were accurate to within 25% of the true cost, with 55% (95% IC: 53–56) overestimating and 21% (95% IC: 20–22) underestimating the true actual cost. The majority (76%) of family physicians thought they did not have or were uncertain as to whether they had adequate knowledge of diagnostic and laboratory test costs, and only 7% reported receiving adequate education. The majority of the family physicians (82%) said that they had adequate access to information about the diagnostic and laboratory test costs. Thirty-three percent thought that costs did not influence their decision to order tests, while 27% were uncertain. Conclusions Portuguese family physicians have limited awareness of diagnostic and laboratory test costs, and our results demonstrate a need for improved education in this area. Further research should focus on identifying whether interventions in cost knowledge actually change ordering behavior, in identifying optimal methods to disseminate cost information, and on improving the cost-effectiveness of care.

Sophistication vs Logical Depth

Sophistication and logical depth are two measures that express how complicated the structure in a string is. Sophistication is defined as the minimal complexity of a computable function that defines a two-part description for the string that is shortest within some precision; the second can be defined as the minimal computation time of a program that is shortest within some precision. We show that the Busy Beaver function of the sophistication of a string exceeds its logical depth with logarithmically bigger precision, and that logical depth exceeds the Busy Beaver function of sophistication with logarithmically bigger precision. We also show that sophistication is unstable in its precision: constant variations can change its value by a linear term in the length of the string.

Digital ulcers in systemic sclerosis: role of flow-mediated dilatation and capillaroscopy as risk assessment tools

AimThe aim of this study was to evaluate macrovascular endothelial dysfunction and microvascular damage as clinical markers of peripheral microangiopathy in patients with Raynaud’s phenomenon (RP).Patients and methodsSeventy-seven secondary RP with systemic sclerosis, 32 primary RP and 34 healthy controls were included in our study. Secondary RP patients were divided into two subgroups: 39 with digital ulcers (DU) and 38 without digital ulcers (non-DU).ResultsPatients with DU had significantly lower flow-mediated dilatation values (5.34 ± 7.49%) compared to non-DU patients (16.21 ± 11.31%), primary RP (17.96 ± 12.78%) and controls (20.17 ± 8.86%), p<0.001, favouring macrovascular endothelium dysfunction. Regarding microvascular damage, the DU group had a predominately capillaroscopic late pattern (71.1%) whereas non-DU patients had an active pattern (56.4%). The microangiopathy evolution score was significantly higher in the DU group compared to the non-DU group (4.79 ± 1.82 vs. 1.79 ± 1.56, p<0.001). Flow-mediated dilation was significantly lower in late pattern (6.13 ± 7.09%) compared to active (12.58 ± 10.66%) and early patterns (17.72 ± 14.90%), p = 0.016 and p = 0.044 respectively.ConclusionsLow flow-mediated dilatation and microvascular damage in capillaroscopy are early clinical markers of DU risk in RP patients.

Diagnostic and laboratory test ordering in Northern Portuguese Primary Health Care: a cross-sectional study

Objectives To characterise the test ordering pattern in Northern Portugal and to investigate the influence of context-related factors, analysing the test ordered at the level of geographical groups of family physicians and at the level of different healthcare organisations. Design Cross-sectional study. Setting Northern Primary Health Care, Portugal. Participants Records about diagnostic and laboratory tests ordered from 2035 family physicians working at the Northern Regional Health Administration, who served approximately 3.5 million Portuguese patients, in 2014. Outcomes To determine the 20 most ordered diagnostic and laboratory tests in the Northern Regional Health Administration; to identify the presence and extent of variations in the 20 most ordered diagnostic and laboratory tests between the Groups of Primary Care Centres and between health units; and to study factors that may explain these variations. Results The 20 most ordered diagnostic and laboratory tests almost entirely comprise laboratory tests and account for 70.9% of the total tests requested. We can trace a major pattern of test ordering for haemogram, glucose, lipid profile, creatinine and urinalysis. There was a significant difference (P<0.001) in test orders for all tests between Groups of Primary Care Centres and for all tests, except glycated haemoglobin (P=0.06), between health units. Generally, the Personalised Healthcare Units ordered more than Family Health Units. Conclusions The results from this study show that the most commonly ordered tests in Portugal are laboratory tests, that there is a tendency for overtesting and that there is a large variability in diagnostic and laboratory test ordering in different geographical and organisational Portuguese primary care practices, suggesting that there may be considerable potential for the rationalisation of test ordering. The existence of Family Health Units seems to be a strong determinant in decreasing test ordering by Portuguese family physicians. Approaches to ensuring more rational testing are needed.

Witness Hiding Without Extractors or Simulators

In a witness hiding protocol the prover tries to convince the verifier that he knows a witness to an instance of an \(\mathbf{NP}\) problem without revealing the witness. We propose a new look at witness hiding based on the information conveyed in each particular instance of the protocol.