Work and Heat

If you are working on New Year's Eve or New Year's Day, odds are it is from home, where you can (usually) control the temperature in the home. Which, from the standpoint of productivity, is a good thing. According to a study from Cornell, raising…

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Curbstoning

Curbstoning, to an established auto dealer, is the practice of unlicensed car dealers selling cars from streetside, where the cars may be parked along the curb.  With a pretense of being an individual selling a car on his or her own, and with no fixed…

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Snowball Sampling

Snowball sampling is a form of sampling in which the selection of new sample subjects is suggested by prior subjects.  From a statistical perspective, the method is prone to high variance and bias, compared to random sampling. The characteristics of the initial subject may propagate through the sample to some degree, and a sample derived by starting with subject 1 may differ from that produced by by starting with subject 2, even if the resulting sample in both cases contains both subject 1 and subject 2.  However, …

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The False Alarm Conundrum

False alarms are one of the most poorly understood problems in applied statistics and biostatistics. The fundamental problem is the wide application of a statistical or diagnostic test in search of something that is relatively rare. Consider the Apple Watch's new feature that detects atrial…

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Conditional Probability Word of the Week

QUESTION:  The rate of residential insurance fraud is 10% (one out of ten claims is fraudulent).  A consultant has proposed a machine learning system to review claims and classify them as fraud or no-fraud.  The system is 90% effective in detecting the fraudulent claims, but only 80% effective in correctly classifying the non-fraud claims (it mistakenly labels one in five as "fraud").  If the system classifies a claim as fraudulent, what is the probability that it really is fraudulent?

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Instructor Spotlight – David Kleinbaum

David Kleinbaum developed several courses for Statistics.com, including Survival Analysis, Epidemiologic Statistics, and Designing Valid Statistical Studies. David retired a little over a year ago from Emory University, where he was a popular and effective teacher with the ability to distill and explain difficult statistical…

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Book Review: Active-Epi

ActivEpi Web, by David Kleinbaum, is the text used in two Statistics.com courses (Epidemiology Statistics and Designing Valid Studies), but it is really a rich multimedia web-based presentation of epidemiological statistics, serving the role of a unique textbook format for an introductory course in the…

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Churn

Churn is a term used in marketing to refer to the departure, over time, of customers.  Subscribers to a service may remain for a long time (the ideal customer), or they may leave for a variety of reasons (switching to a competitor, dissatisfaction, credit card expires, customer moves, etc.).  A customer who leaves, for whatever reason, "churns."

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Survival Analysis

Convinced that he, like his father, would die in his 40's, Winston Churchill lived his early life in a frenetic hurry. He had participated in four wars on three continents by his mid-20's, served in multiple ministerial positions by his 30's, and published 12 books…

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How Google Determines Which Ads you See

A classic machine learning task is to predict something's class, usually binary - pictures as dogs or cats, insurance claims as fraud or not, etc. Often the goal is not a final classification, but an estimate of the probability of belonging to a class (propensity),…

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Job Spotlight: Data Scientist

Data science is one of a host of similar terms. Artificial intelligence has been around since the 1960's and data mining for at least a couple of decades. Machine learning came out of the computer science community, and analytics, data analytics, and predictive analytics came…

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