Blockchain Papers

Henrik Axelsen, Johannes Rude Jensen, Omri Ross

Decentralized Autonomous Organizations (DAOs) have seen exponential growth and interest due to their potential to redefine organizational structure and governance. Despite this, there is a discrepancy between the ideals of autonomy and decentralization and the actual experiences of DAO stakeholders. The Information Systems (IS) literature has yet to fully explore whether DAOs are the optimal organizational choice. Addressing this gap, our research asks, "Is a DAO suitable for your organizational needs?" We derive a gated decision-making framework through a thematic review of the academic and grey literature on DAOs. Through five scenarios, the framework critically emphasizes the gaps between DAOs' theoretical capabilities and practical challenges. Our findings contribute to the IS discourse on blockchain technologies, with some ancillary contributions to the IS literature on organizational management and practitioner literature.

Germán Fierro

Arterial hypertension affects a third of the world's population and is a significant risk factor for cardiovascular disease. Blood pressure (BP) is one of the most relevant parameters used for monitoring of possible hypertension states in patients at risk of cardiovascular disease. Hence, there exists a need for new monitoring solutions, which allow to increase the frequency between BP assessments, but also allow to reduce the level of occlusion in the attempts. Moens-Korteweg equation is among the main principles to estimate BP by dispensing of any inflatable cuff. This principle might lead to an indirect estimation of BP by measuring the time it takes the pressure pulse to propagate between two pre-established vascular points, accordingly the pulse transit time (PTT) method. This thesis proposes a wearable PTT-based method to estimate central aortic BP (CABP) and, the main milestones of this work included: proof of concept of the proposed method (pilot work), the development of a wearable device (including two stages of validation), the proposition of a miniaturized version (integrated circuit) of the analog front-end of the wearable hardware, and, the development of a novel PTT-based model (PTTBM, i.e., the mathematical relationship between measured variables and estimated BP) suitable for the proposed wearable methodology to estimate BP. The main contributions found at each milestone are presented. One of the contributions of this thesis is the use of the PTT-principle for estimating CABP instead of the peripheral BP (PBP) (as typically used in the literature). The pilot work showed the feasibility of CABP estimation from the PTT principle by using electrocardiogram (ECG) and ballistocardiogram (BCG) recordings from off-the-shelf equipment. Results showed that CABP was more correlated with the proposed methodology in comparison to all PBP variables assessed; confirming our hypothesis that the CABP is the most suitable parameter to collate through the time elapsed from ECG R-wave to the BCG J-wave. That is, considered featured time (RJ-interval) includes the time of a pulse pressure propagating at an aortic district. Bland-Altman plots showed an almost zero mean error (\u\ < 0.02mmHg) and bounded standard deviation o < 5mmHg for all systolic and mean central BP readings. Pilot work provided a landmark in order to develop a compact device that allows the integration of wireless blood pressure monitoring into a wearable system. Another contribution of this thesis is the proposition of a wearable device for PTT-computing by also including design considerations for the signal conditioning chains for ECG and BCG signals. The proposed design procedure takes care of minimizing the impact of spurious delays between physiological signals, which eventually degrade the PTT computation. Further, such a procedure could be suitable for any PTT-acquisition. Filtering with low and controlled delay is required for this biomedical application, and proposed conditioning chains provide less than 2ms group-delay, showing the effectiveness of the proposed approach. In order to provide the methodology with higher autonomy and integration, a highly miniaturized implementation of the filtering approach was also proposed. It includes the design of proposed architectures in CMOS technology to implement the particular low-delay filtering at reduced bandwidth featuring ultra-low-power characteristics. Results show that less than 2ms delay for the ECG QRS-complex can be achieved with a total current consumption of IDD = 2:1nA at VDD = 1:2V of power supply. Such development meant another significant contribution of this work in the conception of highly autonomous wearable devices for PTT acquisition. The first stage of validations on the wearable CABP estimation showed that, when considering data from one volunteer, results achieved with off-the-shelf equipment could be replicated by using a proposed wearable device, and the method could be further validated by using the wearable version. Additionally, CABP estimation from the proposed wearable device could be feasible by using three feature times (FTs) as CABP surrogates; that is, RI, RJ, and IJ intervals (from ECG and BCG wearable recordings). The first validation of the method also showed that CABP could be accurately predicted by the proposed methodology when in the order of daily calibrations are performed. The second stage of validations involved a study with a group of volunteers, and new alternatives were explored (twentyseven: nine PTTBMs along the three FTs) for the CABP estimation. We found that CABP could be accurately estimated (inside AAMI requirements) through the presented methodology by using four of the explored alternatives, whereas the RI interval, an FT lacking any PTT assessment, emerged as the best surrogate for the CABP estimation. Hence, a principle different from the traditional PTT-based method arises as a more advantageous method for the CABP estimation in the light of evidence reported in this validation, and, to our knowledge, this is the first time that CABP has been successfully estimated from a wearable device. The final significant contribution of this thesis meant the last chain-link in the process to achieve an utterly original method to estimate CABP. A novel PTTBM to estimate CABP is proposed, which uses a ow-driven two-element Windkesel network constructed from FTs extracted from the wearable recordings. When classic PTTBMs are applied, the fitting of parameters often leads to values without a physiological basis. Opposite to that in the proposed PTTBM, the parameters have a clear physiological meaning, and the parameter fitting led to values that are consistent with this meaning and more stable throughout calibrations. In conclusion, this thesis introduces a novel device that exploits an alternative and indirect method for CABP estimation. Variants of the principle used, accordingly, PTT method, have been previously explored to estimate PBP but not for central aortic BP. Additionally, the device was designed to be wearable; that is, it is attached to the clothes, causing low discomfort for the user during the measurement, thus, allowing continuous and ambulatory monitoring of aortic pressure. The developed wearable system, validated in a series of volunteers, showed promising results towards the continuous CABP monitoring.

J O'donnell

Although the problems identified in the statement have been known for several decades, previous expressions of concern and calls for action have not fostered broad improvements in practice.2 A P value of 0.05 carries a 5% risk of a false positive result (i.e. there is no true difference between treatments). If a trial is meant to provide proof of a genuine treatment difference beyond reasonable doubt, a much smaller P value – say p < 0. 001 – is required.5 We disagree ….that our statement… is erroneous. According to the null hypothesis, P < 0.05 will occur 5% of the time.6 No editorial corrigendum has appeared. A P-value is the area under the curve of a probability distribution defined by a mathematical model. The model, usually presented graphically, describes the expected distribution of a sample statistic around a central measure, the parameter or theoretical ‘true’ value, for example the population mean, μ. Under the central limit theorem, this would be the standard normal distribution of sample means generated by repeat sampling of a population variable of interest. The mean of the sample means would equal the ‘true’ population mean, μ. In medicine, it is rare for us ever to know the true value of the variable of interest. However, we can usefully assign a value in the special case of a difference statistic, for example the difference in mean outcome variables in a placebo-controlled drug trial. In this case, the sampling distribution would represent that of the difference statistic. In this case, if the value we assign μ is zero then the mathematical model becomes the null hypothesis used in NHST. By way of contrast, non-inferiority drug trials require a non-zero value to be assigned. The cumulative AUC of the sampling distribution of a continuous variable is represented by a mathematical function called the cumulative density function. In medical science, most study variables are continuous or, if categorical, are transformed using the logit model. As the P-value is a mathematical integral, that is the cumulative AUC, it cannot take on a precise value as there is no AUC defined by a single point on the curve, for example the P-value ≤ 0.05, but not P = 0.05. While this may seem pedantic, the semantics of statistical inference are influential in thinking and decision-making yet misinterpretation and misuse of terminology are commonplace. Under the null hypothesis, one sample mean that happens to fall within an extreme region of the standard normal distribution may be expected to occur with a low frequency, say P ≤ 0.05 meaning such a sample mean or one more extreme would be expected to occur with a frequency of 5% or less. To be valid, the assumptions of independence and random selection of each sample mean selected from the normal distribution of sample means must be assumed. Another way of stating this is as a conditional probability: . Note: | means ‘given’. It is important to understand that the P-value is a measure conditional on the assumption that the mathematical model describes the distribution of sample means and is not a measure of the probability of the ‘truth’ of the mathematical model. To make this claim would invert the conditional probability statement and commit an error of reasoning called transposing the conditional7 aka the prosecutor's fallacy: . In reasoning from NHST, the commonly used definition of the P-value as ‘a measure of evidence against the null hypothesis’ is potentially misleading in that it seems to legitimise transposing the conditional as if it were a mathematically valid function rather than a matter of intuition. It was the intuitive interpretation that Fisher used in his a posteriori model of NHST.8, 9 His aim was to use the P-value as an aid in deciding which experiments to repeat. If on several repetitions, a consistent extreme P-value for the sample statistic was obtained then that would accumulate evidence for a true experimental effect. If no such effect was present, regression to the mean parameter (μ) would be expected (P ≥ 0.05). In real-life scenarios, many factors inhibit repetition and replication of experiments; however, modelling can give us insight into the precision and reproducibility of extreme P-values10, 11 and hence the intuitive weight we place on the P-value ‘as a measure of evidence against the null hypothesis’. Table 2 is a reproduction.10 It describes the results of simulating repeat experimentation and the probability of producing a P-value ≤ 0.05 under the prescribed conditions of the simulated experiment. It may be surprising to many how poorly reproducible the P-value is as a bright line test (a bright line test is a clearly defined rule or standard, the purpose of which is to produce consistent and predictable results). For example, if in the first experiment P ≤ 0.05 was produced there would be a 50% probability of reproducing P ≤ 0.05 in a repeat experiment; if P ≤ 0.01was produced in the first experiment the probability of producing P ≤ 0.05 in a repeat experiment, would be 73%; and if P ≤ 0.001 was produced in the first experiment the probability of P ≤ 0.05 in a repeat experiment would be 91%. The magnitudes of a number of these first experiment P-values are those commonly used in pharmaceutical trials and other medical analyses. The P-value is also sensitive to sample size. Irrespective of the effect size, with increasing sample size (n) the P-value can be made as small as you wish12 because the standard error is proportional to the inverse of n. If statistical significance is substituted for ‘clinical significance’ even small irrelevant differences may be regarded as worthy of investment. Large sample sizes are often a feature of pharmaceutical trials of secondary and primary prevention interventions such as preventive therapies in atherosclerotic diseases and osteoporosis. The quoted extract from the article on clinical trials mistakenly promotes the P-value as a measure of error and further states that the error rate can legitimately be adjusted depending on the magnitude of the P-value thus providing ‘proof of a genuine treatment difference beyond reasonable doubt’. This erroneous interpretation has arisen from the illusion of coherence resulting from the conflation of the dominant models of hypothesis testing.8, 9 The setting of theoretical type 1 (α) and type 2 (β) error rates in the Neyman and Pearson model envisions the frequency of error ‘in the long run of experience’ (experimental repetition) given randomness and independence of sample means from two juxtaposed probability distributions. A priori two identical populations are imagined except that they differ in mean parameters, null μ0 and alternative μA. This model is valuable in providing a rationality to sample size selection. However, the conflation has resulted in confusion between Fisher's P-value and Neyman's α giving the P-value an apparent legitimacy as an a posteriori ‘sliding’ type 1 error rate. Even if this were logical, decreasing α would increase β, resulting in a decrease in power (1-β). Also the dichotomous approach of pitting null hypothesis against alternative hypothesis carries the risk of blinding the researcher or the consumer to other explanatory hypotheses. For those who think the use of confidence intervals (CI) overcomes the problems described, think again. Although it has greater intuitive value especially with respect to estimating effect size, the CI relies on the same premises as the P-value. For example the CI of juxtaposed probability distributions can be made as large or as small as can be paid for by increasing the sample size such that for any small difference the CI can be made not to overlap. Statistical analyses are very valuable tools for extracting information from data. However, the reliability of the knowledge generated is dependent on many more important factors inter alia, evidential justification of the experimental hypothesis, study design, study conduct and data collection and cleansing, competence in choice of statistical model, valid reasoning, reviewer bias, publication bias and replication. Much of the criticism of medical science centres on its overemphasis on the importance of the P-value, NHST and statistically defined effect sizes. A better understanding of how sound statistical inferences are made and how they influence decision making will be key elements to improving all aspects of healthcare. This is critically important in acknowledgement of individuals as complex adaptive systems with characteristics of emergence, adaptability, non-linearity and unpredictability13 rather than as static population averages. Surveys suggest statistical literacy amongst doctors is low.14, 15 Teaching and assessing knowledge and application of statistical inference, critical appraisal and decision-making skills should be a primary focus of medical schools and specialist colleges. Difficult concepts underpinning statistical inference may be more effectively and efficiently taught using computer simulation whereby the learner can manipulate effect sizes, sample sizes and other statistics in order to see how parameter estimates, P-values and CI change with reproduction and replication.16 This will foster a more in-depth understanding of the limits of statistical inference, making clinicians better able to choose wisely amongst the myriad of investigations and treatment options on offer. Subsequent to article submission and review the author attended the referenced ASA conference.2 A special issue of the ASA journal reporting the conference proceedings is planned for 2018. In the opening addresses, the 400 participants were encouraged to devote their energies to developing proposals and goals to address the long standing yet stubbornly persistent errors in statistical inference described in this article. While concrete proposals are yet to be endorsed by the ASA, many speakers emphasised the need to place greater emphasis on teaching the conceptual framework of the different philosophical approaches to science (mastering the concepts as a priority rather than the mechanics of statistical inference). The need for better understanding of statistical semantics on the part of non-statistician scientists was also highlighted. Further that the best way to achieve understanding would be to develop context-specific learning modules. An aspect of the conference that resonated with the author with respect to prediction in medical science was the idea that science defines degrees of uncertainty (not certainty) apropos caution must be applied to the use of prediction models in medical practice lest they be over-extended.

Frank C. Day, David L. Schriger

Discussion Points1Cruz et al1Cruz C.O. Meshberg E.G. Shofer F.S. et al.Interrater reliability and accuracy of clinicians and trained research assistants performing prospective data collection in emergency department patients with potential acute coronary syndrome.Ann Emerg Med. 2009; 54: 1-7Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar contains 2 parts, a comparison of the values gathered by trained research assistants and physicians about historical information in chest pain patients and the comparison of these participants' recordings with a “correct” value for each item.A. For each part, indicate whether the authors are studying reliability or validity and explain the difference between these concepts.B. What did the authors use as their criterion standard for the validity analysis?C. What are potential problems with their method of defining the criterion (gold) standard? Can you think of alternative approaches?D. The authors report crude agreement and interquartile range for their validity analysis. What part of a distribution is described by the interquartile range? List other statistics used to describe the validity of a measure and why they might be preferable to reporting crude agreement.2Tabled 1MD Recorded “Yes”MD Recorded “No”TotalRA recorded yes1176123RA recorded no18220Total1358143MD, Medical doctor; RA, research assistant. Open table in a new tab A. Calculate the crude percentage agreement for this table. What is the range of possible values for percentage agreement?B. Calculate Cohen's κ for this table. What is the formula for κ for raters making a binary assessment (eg, yes/no or true/false)? Discuss the purpose of Cohen's κ, its range, and the interpretations of key values such as –1, 0, and 1.C. What other measures can be used to measure reliability for binary, categorical, and continuous data? 3Cruz et al quote the oft-cited Landis and Koch2Landis J.R. Koch G.C. The measurement of observer agreement for categorical data.Biometrics. 1977; 33: 159-174Crossref PubMed Scopus (49675) Google Scholar article stating that a κ of “less than 0.2 represents poor agreement; 0.21 to 0.40, fair agreement; 0.41 to 0.60, moderate agreement; 0.61 to 0.80, good agreement; and 0.81 to 1.00, excellent agreement.” Consider studies of the agreement of airline pilots deciding whether it is safe to land and psychologists deciding whether interviewees have type A or type B personalities. the studies the κ the by Landis and Koch be 2 are in of a and to such as is a a or by a in the for and in the for are and the are to a for each that they percentage agreement is and κ is of are and are that the is the for a the the this the percentage agreement and κ for the the of the are and of the are by the of the are and of the are by the the are and of the are by the and of the are and of the are by the Discuss the of percentage agreement and κ in these Consider the 2 and percentage agreement and κ for is κ the What this that the table the described and that that to 2 in the raters are that are and the raters are that be with with or in with each of κ the in these 2 the of κ, that such that and or are for the and percentage agreement and κ for these is the measure for Consider the of the raters in the in this be reliability is might this be the percentage agreement κ for the in of et The are to indicate the in the and 2 Open table in a new tab A. in the table are with the the pain it to the it to the it to the for these Can you explain why these have percentage agreement you is the the Can you the between the of the in the table and the to κ percentage the problems with percentage agreement and κ in these you think it be the in the of each table of reporting the percentage agreement or et al contains 2 parts, a comparison of the values gathered by trained research assistants and physicians historical information in chest pain and the comparison of these participants' recordings with a “correct” value for each For each part, indicate whether the authors are studying reliability or validity and explain the difference between these part is assessment of and the is assessment of The between reliability and validity is the that the in a that a a The reliability of a to the agreement the the or assessment of validity a observer a or the criterion standard is to be validity studies report the of the observer statistics such as and or reliability such as percentage agreement or What did the authors use as their criterion standard for the validity the and the research it is that their is they a research the of the 2 is What are potential problems with their method of defining the standard? 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Meshberg E.G. Shofer F.S. et al.Interrater reliability and accuracy of clinicians and trained research assistants performing prospective data collection in emergency department patients with potential acute coronary syndrome.Ann Emerg Med. 2009; 54: 1-7Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar contains 2 parts, a comparison of the values gathered by trained research assistants and physicians about historical information in chest pain patients and the comparison of these participants' recordings with a “correct” value for each item.A. For each part, indicate whether the authors are studying reliability or validity and explain the difference between these concepts.B. What did the authors use as their criterion standard for the validity analysis?C. What are potential problems with their method of defining the criterion (gold) standard? Can you think of alternative approaches?D. The authors report crude agreement and interquartile range for their validity analysis. What part of a distribution is described by the interquartile range? List other statistics used to describe the validity of a measure and why they might be preferable to reporting crude agreement.2Tabled 1MD Recorded “Yes”MD Recorded “No”TotalRA recorded yes1176123RA recorded no18220Total1358143MD, Medical doctor; RA, research assistant. Open table in a new tab A. Calculate the crude percentage agreement for this table. What is the range of possible values for percentage agreement?B. Calculate Cohen's κ for this table. What is the formula for κ for raters making a binary assessment (eg, yes/no or true/false)? Discuss the purpose of Cohen's κ, its range, and the interpretations of key values such as –1, 0, and 1.C. What other measures can be used to measure reliability for binary, categorical, and continuous data? 3Cruz et al quote the oft-cited Landis and Koch2Landis J.R. Koch G.C. The measurement of observer agreement for categorical data.Biometrics. 1977; 33: 159-174Crossref PubMed Scopus (49675) Google Scholar article stating that a κ of “less than 0.2 represents poor agreement; 0.21 to 0.40, fair agreement; 0.41 to 0.60, moderate agreement; 0.61 to 0.80, good agreement; and 0.81 to 1.00, excellent agreement.” Consider studies of the agreement of airline pilots deciding whether it is safe to land and psychologists deciding whether interviewees have type A or type B personalities. the studies the κ the by Landis and Koch be 2 are in of a and to such as is a a or by a in the for and in the for are and the are to a for each that they percentage agreement is and κ is of are and are that the is the for a the the this the percentage agreement and κ for the the of the are and of the are by the of the are and of the are by the the are and of the are by the and of the are and of the are by the Discuss the of percentage agreement and κ in these Consider the 2 and percentage agreement and κ for is κ the What this that the table the described and that that to 2 in the raters are that are and the raters are that be with with or in with each of κ the in these 2 the of κ, that such that and or are for the and percentage agreement and κ for these is the measure for Consider the of the raters in the in this be reliability is might this be the percentage agreement κ for the in of et The are to indicate the in the and 2 Open table in a new tab A. in the table are with the the pain it to the it to the it to the for these Can you explain why these have percentage agreement you is the the Can you the between the of the in the table and the to κ percentage the problems with percentage agreement and κ in these you think it be the in the of each table of reporting the percentage agreement or et al1Cruz C.O. Meshberg E.G. Shofer F.S. et al.Interrater reliability and accuracy of clinicians and trained research assistants performing prospective data collection in emergency department patients with potential acute coronary syndrome.Ann Emerg Med. 2009; 54: 1-7Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar contains 2 parts, a comparison of the values gathered by trained research assistants and physicians about historical information in chest pain patients and the comparison of these participants' recordings with a “correct” value for each item.A. For each part, indicate whether the authors are studying reliability or validity and explain the difference between these concepts.B. What did the authors use as their criterion standard for the validity analysis?C. What are potential problems with their method of defining the criterion (gold) standard? Can you think of alternative approaches?D. The authors report crude agreement and interquartile range for their validity analysis. What part of a distribution is described by the interquartile range? List other statistics used to describe the validity of a measure and why they might be preferable to reporting crude agreement.2Tabled 1MD Recorded “Yes”MD Recorded “No”TotalRA recorded yes1176123RA recorded no18220Total1358143MD, Medical doctor; RA, research assistant. Open table in a new tab A. Calculate the crude percentage agreement for this table. What is the range of possible values for percentage agreement?B. Calculate Cohen's κ for this table. What is the formula for κ for raters making a binary assessment (eg, yes/no or true/false)? Discuss the purpose of Cohen's κ, its range, and the interpretations of key values such as –1, 0, and 1.C. What other measures can be used to measure reliability for binary, categorical, and continuous data? 3Cruz et al quote the oft-cited Landis and Koch2Landis J.R. Koch G.C. The measurement of observer agreement for categorical data.Biometrics. 1977; 33: 159-174Crossref PubMed Scopus (49675) Google Scholar article stating that a κ of “less than 0.2 represents poor agreement; 0.21 to 0.40, fair agreement; 0.41 to 0.60, moderate agreement; 0.61 to 0.80, good agreement; and 0.81 to 1.00, excellent agreement.” Consider studies of the agreement of airline pilots deciding whether it is safe to land and psychologists deciding whether interviewees have type A or type B personalities. the studies the κ the by Landis and Koch be 2 are in of a and to such as is a a or by a in the for and in the for are and the are to a for each that they percentage agreement is and κ is of are and are that the is the for a the the this the percentage agreement and κ for the the of the are and of the are by the of the are and of the are by the the are and of the are by the and of the are and of the are by the Discuss the of percentage agreement and κ in these Consider the 2 and percentage agreement and κ for is κ the What this that the table the described and that that to 2 in the raters are that are and the raters are that be with with or in with each of κ the in these 2 the of κ, that such that and or are for the and Calculate percentage agreement and κ for these is the measure for Consider the of the raters in the in this be reliability is might this be the percentage agreement κ for the in of et The are to indicate the in the and 2 Open table in a new tab A. in the table are with the the pain it to the it to the it to the for these Can you explain why these have percentage agreement you is the the Can you the between the of the in the table and the to κ percentage the problems with percentage agreement and κ in these you think it be the in the of each table of reporting the percentage agreement or et al contains 2 parts, a comparison of the values gathered by trained research assistants and physicians historical information in chest pain and the comparison of these participants' recordings with a “correct” value for each For each part, indicate whether the authors are studying reliability or validity and explain the difference between these part is assessment of and the is assessment of The between reliability and validity is the that the in a that a a The reliability of a to the agreement the the or assessment of validity a observer a or the criterion standard is to be validity studies report the of the observer statistics such as and or reliability such as percentage agreement or What did the authors use as their criterion standard for the validity the and the research it is that their is they a research the of the 2 is What are potential problems with their method of defining the standard? 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