ENTRIES TAGGED "machine learning"
Organize solutions into clusters and “force multiply” feedback provided by instructors
One of the hardest things about teaching a large class is grading exams and homework assignments. In my teaching days a “large class” was only in the few hundreds (still a challenge for the TAs and instructor). But in the age of MOOCs, classes with a few (hundred) thousand students aren’t unusual.
Researchers at Stanford recently combed through over one million homework submissions from a large MOOC class offered in 2011. Students in the machine-learning course submitted programming code for assignments that consisted of several small programs (the typical submission was about 16 lines of code). While over 120,000 enrolled only about 10,000 students completed all homework assignments (about 25,000 submitted at least one assignment).
The researchers were interested in figuring out ways to ease the burden of grading the large volume of homework submissions. The premise was that by sufficiently organizing the “space of possible solutions”, instructors would provide feedback to a few submissions, and their feedback could then be propagated to the rest.
Accuracy, simplicity, speed, and interpretability are some of the factors that need to be considered
For companies in the early stages of grappling with big data, the analytic lifecycle (model building, deployment, maintenance) can be daunting. In earlier posts I highlighted some new tools that simplify aspects of the analytic lifecycle, including the early phases of model building. But while tools are allowing companies to offload routine analytic tasks to business analysts, experienced modelers are still needed to fine-tune and optimize, mission-critical algorithms.
Model Selection: Accuracy and other considerations
Accuracy1 is the main objective and a lot of effort goes towards raising it. But in practice tradeoffs have to be made, and other considerations play a role in model selection. Speed (to train/score) is important if the model is to be used in production. Interpretability is critical if a model has to be explained for transparency2 reasons (“black-boxes” are always an option, but are opaque by definition). Simplicity is important for practical reasons: if a model has “too many knobs to tune” and optimizations have to be done manually, it might be too involved to build and maintain it in production3.
Chances are a model that’s fast, easy to explain (interpretable), and easy to tune (simple), is less4 accurate. Experienced model builders are valuable precisely because they’ve weighed these tradeoffs across many domains and settings. Unfortunately not many companies have the experts that can identify, build, deploy, and maintain models at scale. (An example from Google illustrates the kinds of issues that can come up.)
Tools simplify the application of advanced analytics and the interpretation of results
A new set of tools make it easier to do a variety of data analysis tasks. Some require no programming, while other tools make it easier to combine code, visuals, and text in the same workflow. They enable users who aren’t statisticians or data geeks, to do data analysis. While most of the focus is on enabling the application of analytics to data sets, some tools also help users with the often tricky task of interpreting results. In the process users are able to discern patterns and evaluate the value of data sources by themselves, and only call upon expert1 data analysts when faced with non-routine problems.
Visual Analysis and Simple Statistics
Three SaaS startups – DataHero, DataCracker, Statwing – make it easy to perform simple data wrangling, visual analysis, and statistical analysis. All three (particularly DataCracker) appeal to users who analyze consumer surveys. Statwing and DataHero simplify the creation of Pivot Tables2 and suggest3 charts that work well with your data. StatWing users are also able to execute and view the results of a few standard statistical tests in plain English (detailed statistical outputs are also available).
Statistics and Machine-learning
BigML and Datameer’s Smart Analytics are examples of recent tools that make it easy for business users to apply machine-learning algorithms to data sets (massive data sets, in the case of Datameer). It makes sense to offload routine data analysis tasks to business analysts and I expect other vendors such as Platfora and ClearStory to provide similar capabilities in the near future.
Health data can go beyond the averages and first order patient characteristics to find long-term trends
This article was written with Arijit Sengupta, CEO of BeyondCore. Tim and Arijit will speak at Strata Rx 2013 on the topic of this post.
Current healthcare cost prevention efforts focus on the top 1% of highest risk patients. As care coordination efforts expand to a larger set of the patient population, the critical question is: If you’re a care manager, which patients should you offer additional care to at any given point in time? Our research shows that focusing on patients with the highest risk scores or highest current costs create suboptimal roadmaps. In this article we share an approach to predict patients whose costs are about to skyrocket, using a hypothesis-free micro-segmentation analysis. From there, working with physicians and care managers, we can formulate appropriate interventions.
Arijit Sengupta of BeyondCore uncovers hidden relationships in public health data
The importance of visualizing data is universally recognized. But, usually the data is passive input to some visualization tool and the users have to specify the precise graph they want to visualize. BeyondCore simplifies this process by automatically evaluating millions of variable combinations to determine which graphs are the most interesting, and then highlights these to users. In essence, BeyondCore automatically tells us the right questions to ask of our data.
In this video, Arijit Sengupta, CEO of BeyondCore, describes how public health data can be analyzed in real-time to discover anomalies and other intriguing relationships, making them readily accessible even to viewers without a statistical background. Arijit will be speaking at Strata Rx 2013 with Tim Darling of Objective Health, a McKinsey Solution for Healthcare Providers, on the topic of this post.
Compelling large-scale data platforms originate from the world of IT Operations
I’ve been noticing that many interesting big data systems are coming out of IT operations. These are systems that go beyond the standard “capture/measure, display charts, and send alerts”. IT operations has long been a source of many interesting big data1 problems and I love that it’s beginning to attract the attention2 of many more data scientists and data engineers.
It’s not surprising that many of the interesting large-scale systems that target time-series and event data have come from ops teams: in an earlier post on time-series, several of the tools I highlighted came out of IT operations. IT operations involves monitoring many different hardware and software systems, a task that requires a variety of tools and which quickly leads to “metrics overload”. A partial list includes data captured from a wide range of application log files, network traffic, energy and power sources.
The volume of IT ops data has led to new tools like OpenTSDB and KairosDB – time series databases that leverage HBase and Cassandra. But storage, simple charts, and lookups are just the foundation of what’s needed. IT Ops track many interdependent systems, some of which might be correlated3. Not only are IT ops faced with highlighting “unknown unknowns” in their massive data sets, they often need to do so in near realtime.
Volume, variety, velocity, and a rare peek inside sponsored search advertising at Google
The $35B merger of Omnicom and Publicis put the convergence of Big Data and Advertising1 in the front pages of business publications. Adtech2 companies have long been at the forefront of many data technologies, strategies, and techniques. By now it’s well-known that many impressive large scale, realtime analytics systems in production, support3 advertising. A lot of effort has gone towards accurately predicting and measuring click-through rates, so at least for online advertising, data scientists and data engineers have gone a long way towards addressing4 the famous “but we don’t know which half” line.
The industry has its share of problems: privacy & creepiness come to mind, and like other technology sectors adtech has its share of “interesting” patent filings (see for example here, here, here). With so many companies dependent on online advertising, some have lamented the industry’s hold5 on data scientists. But online advertising does offer data scientists and data engineers lots of interesting technical problems to work on, many of which involve the deployment (and creation) of open source tools for massive amounts of data.
Areas concerned with shapes, invariants, and dynamics, in high-dimensions, are proving useful in data analysis
I’ve been noticing unlikely areas of mathematics pop-up in data analysis. While signal processing is a natural fit, topology, differential and algebraic geometry aren’t exactly areas you associate with data science. But upon further reflection perhaps it shouldn’t be so surprising that areas that deal in shapes, invariants, and dynamics, in high-dimensions, would have something to contribute to the analysis of large data sets. Without further ado, here are a few examples that stood out for me. (If you know of other examples of recent applications of math in data analysis, please share them in the comments.)
Compressed sensing is a signal processing technique which makes efficient data collection possible. As an example using compressed sensing images can be reconstructed from small amounts of data. Idealized Sampling is used to collect information to measure the most important components. By vastly decreasing the number of measurements to be collected, less data needs to stored, and one reduces the amount of time and energy1 needed to collect signals. Already there have been applications in medical imaging and mobile phones.
The problem is you don’t know ahead of time which signals/components are important. A series of numerical experiments led Emanuel Candes to believe that random samples may be the answer. The theoretical foundation as to why a random set of signals would work, where laid down in a series of papers by Candes and Fields Medalist Terence Tao2.
We should raise our collective expectations of what they should provide
There is a tremendous amount of commercial attention on machine learning (ML) methods and applications. This includes product and content recommender systems, predictive models for churn and lead scoring, systems to assist in medical diagnosis, social network sentiment analysis, and on and on. ML often carries the burden of extracting value from big data.
But getting good results from machine learning still requires much art, persistence, and even luck. An engineer can’t yet treat ML as just another well-bahaved part of the technology stack. There are many underlying reasons for this, but for the moment I want to focus on how we measure or evaluate ML systems.
Reflecting their academic roots, machine learning methods have traditionally been evaluated in terms of narrow quantitative metrics: precision, recall, RMS error, and so on. The data-science-as-competitive-sport site Kaggle has adopted these metrics for many of its competitions. They are objective and reassuringly concrete.