Visual Detection of Structural Changes in Time-Varying Graphs Using Persistent Homology

Topological data analysis is an emerging area in exploratory data analysis and data mining. Its main tool, persistent homology, has become a popular technique to study the structure of complex, high-dimensional data. In this paper, we propose a novel method using persistent homology to quantify structural changes in time-varying graphs. Specifically, we transform each instance of the time-varying graph into metric spaces, extract topological features using persistent homology, and compare those features over time. We provide a visualization that assists in time-varying graph exploration and helps to identify patterns of behavior within the data. To validate our approach, we conduct several case studies on real world data sets and show how our method can find cyclic patterns, deviations from those patterns, and one-time events in time-varying graphs. We also examine whether persistence-based similarity measure as a graph metric satisfies a set of well-established, desirable properties for graph metrics

Do Households Benefit from Financial Deregulation and Innovation? The Case of the Mortgage Market

The U.S. mortgage market has experienced phenomenal change over the last 35 years. Most observers believe that the deregulation of the banking industry and financial markets generally has played an important part in this transformation. This paper develops and implements a technique for assessing the impact of changes in the mortgage market on individuals and households. Our analysis is based on an implication of the permanent income hypothesis: that the higher a household’s future income, the more it desires to spend and consume, ceteris paribus. If we have perfect credit markets, then desired consumption matches actual consumption and current spending on housing should forecast future income. Since credit market imperfections mute this effect, we can view the strength of the relationship between housing spending and future income as a measure of the “imperfectness” of mortgage markets. Thus, a natural way to determine whether mortgage market developments have actually helped households by decreasing market imperfections is to see whether this link has strengthened over time. We implement this framework using panel data going back to 1969. We find that over the past several decades, housing markets have become less imperfect in the sense that households are now more able to buy homes whose values are consistent with their long-term income prospects. One issue that has received particular attention is the role that the housing Government Sponsored Enterprises (GSEs), Fannie Mae and Freddie Mac, have played in improving the market for housing finance. We find no evidence that the GSEs’ activities have contributed to this phenomenon. This is true whether we look at all homebuyers, or at subsamples of the population whom we might expect to benefit particularly from GSE activity, such as lowincome households and first-time homebuyers.

Do Households Benefit from Financial Deregulation and Innovation? The Case of the Mortgage Market

The U.S. mortgage market has experienced phenomenal change over the last 35 years. This paper develops and implements a technique for assessing the impact of changes in the mortgage market on households. Our framework, which is based on the permanent income hypothesis, that allows us to gauge the importance of borrowing constraints by estimating the empirical relationship between the value of a household's home purchase and its future income. We find that over the past several decades, housing markets have become less imperfect in the sense that households are now more able to buy homes whose values are consistent with their long-term income prospects. One issue that has received particular attention is the role that the housing Government Sponsored Enterprises (GSEs), Fannie Mae and Freddie Mac, have played in improving the market for housing finance. We find no evidence that the GSEs' activities have contributed to this phenomenon. This is true whether we look at all homebuyers, or at subsamples of the population whom we might expect to benefit particularly from GSE activity, such as low-income households and first-time homebuyers.

Persistent Homology Guided Force-Directed Graph Layouts

Graphs are commonly used to encode relationships among entities, yet their abstractness makes them difficult to analyze. Node-link diagrams are popular for drawing graphs, and force-directed layouts provide a flexible method for node arrangements that use local relationships in an attempt to reveal the global shape of the graph. However, clutter and overlap of unrelated structures can lead to confusing graph visualizations. This paper leverages the persistent homology features of an undirected graph as derived information for interactive manipulation of force-directed layouts. We first discuss how to efficiently extract 0-dimensional persistent homology features from both weighted and unweighted undirected graphs. We then introduce the interactive persistence barcode used to manipulate the force-directed graph layout. In particular, the user adds and removes contracting and repulsing forces generated by the persistent homology features, eventually selecting the set of persistent homology features that most improve the layout. Finally, we demonstrate the utility of our approach across a variety of synthetic and real datasets

Evaluating comfort measures for commonly performed painful procedures in pediatric patients.

Introduction: Management of pediatric pain from medical procedures is of great importance for improving both patient care and experience. In this study, we investigated methods of managing acute pain in infants and children by studying the correlation between the number of attempts to complete painful procedures, given different comfort measures. Methods: The study is a retrospective review of 74,276 procedures performed at two pediatric hospitals in an integrated academic children\u27s health system between 2013 and 2016. We compared three comfort measures most frequently offered: positions of comfort (POC), distraction (DIST), and pharmacological (PHARM). These methods were compared in the setting of four procedures: peripheral intravenous (PIV) catheter insertion, gastrointestinal tube placement, incision procedures, and bladder catheterization. We used the number of attempts needed to complete a procedure as a measure of efficacy minimizing distressing experience in an acutely painful setting (single attempt vs repeat attempts). Results: Among younger children, DIST appears superior to the other two methods; it performs significantly better for three of the four procedures (PIV catheterization, incision wound, and urinary catheterization) among infants agedchildren, POC tends to perform slightly better than the other two methods, although it is significantly better only for PIV catheterization among adolescents aged 13-21 years and urinary catheterization among children aged 9-12 years. Conclusion: Results from this study may be used to determine appropriate comfort measures for painful procedures in pediatric setting

Exploring patient and family satisfaction in pediatric neurological surgery

Introduction Patient and family satisfaction during outpatient visits is correlated with a continuance of care and likelihood to recommend the practice to others. Additionally, patient-family satisfaction can determine the success of the practice and influence medical outcomes. Utilizing a well-validated surveys instrument, patient and family satisfaction can be explored in the office setting. Methods During a consecutive 36 month period, a standardized and validated patient satisfaction survey instrument was provided to the family members of patients who presented to two pediatric neurosurgery clinics associated with Nemours Children\u27s Health System. The completed surveys were analyzed statistically to identify correlations between overall satisfaction, defined as “Likelihood to Recommend (LTR) the Practice”, and relevant practice and provider variables. Results The factors that exhibited the greatest correlation to LTR were: ‘Cheerfulness of Practice’ (r = 0.74), ‘Ability to Get Desired Appointment’ (r = 0.70), ‘Likelihood of Recommending Care Provider’ (r = 0.65), ‘Staff Worked Together’ (r = 0.65), and ‘Waiting Area Comfort and Pleasantness’ (r = 0.60). Discussion and conclusions Patient and family satisfaction surveys are useful for gaining insight into pediatric neurosurgical practices. Data from this cohort suggest that the environment in which patient care is delivered, timeliness of appointments and positive perceptions of the healthcare team correlate most strongly with overall satisfaction. © 201