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In this work, we check whether a deep learning model that does rainfall prediction using a variety of sensor readings behaves reasonably. Unlike traditional numerical weather prediction models that encode the physics of rainfall, our model relies purely on data and deep learning.
Can we trust the model? Or should we take a rain check?
We perform two types of analysis. First, we perform a one-at-a-time sensitivity analysis to understand properties of the input features. Holding all the other features fixed, we vary a single feature from its minimum to its maximum value and check whether the predicted rainfall obeys conventional intuition (e.g. more lightning implies more rainfall). Second, for specific prediction at a certain location, we use an existing feature attribution technique to identify influential features (sensor readings) from this and other locations. Again, we check whether the feature importances match conventional wisdom. (e.g. is ‘instant reflectivity’, a measure of the current rainfall more influential than say surface temperature). We compute influence both on the predictions of the model, but also on the error; the latter is perhaps a novel contribution to the literature on feature attribution.
The model we chose to analyze is not the state of the art. It is flawed in several ways, and therefore makes for an interesting analysis target. We find several interesting issues. However, we should clarify that our analysis is not an indictment of machine learning approaches; indeed we know of better models ourselves. But our goal is to demonstrate an interactive analysis technique.
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We study the attribution problem (cf. ~\cite{SVZ13}) for deep networks applied to \emph{perception tasks}. Traditionally, the attribution problem is formulated as blaming the network's prediction on the pixels of the input image, i.e., the \emph{space} dimension. Often, signal is also present in the \emph{scale/frequency} dimension. We propose a new technique called \emph{Blur Integrated Gradients} that produces attributions in both space and in scale. Furthermore, we use the scale-space axioms (cf.~\cite{Lindeberg}) to argue that the input perturbations used by Blur Integrated Gradients will not accidentally create features. There resulting explanations are cleaner, and more faithful to how deep networks operate. We compare against some previously proposed techniques and demonstrate applications on three tasks: ImageNet object recognition, Diabetic Retinopathy prediction, and AudioSet audio event identification.
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The problem of attributing a deep network’s prediction to its input/base features is
well-studied (cf. Simonyan et al. (2013)). We introduce the notion of conductance
to extend the notion of attribution to understanding the importance of hidden units.
Informally, the conductance of a hidden unit of a deep network is the flow of attribution
via this hidden unit. We can use conductance to understand the importance of
a hidden unit to the prediction for a specific input, or over a set of inputs. We justify
conductance in multiple ways via a qualitative comparison with other methods,
via some axiomatic results, and via an empirical evaluation based on a feature
selection task. The empirical evaluations are done using the Inception network
over ImageNet data, and a convolutinal network over text data. In both cases, we
demonstrate the effectiveness of conductance in identifying interesting insights
about the internal workings of these networks.
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We study interactions among players in cooperative games. We propose a new interaction index called Shapley-Taylor Interaction index. It decomposes the value of the game into terms that model the interactions betweensubsets of players in a manner analogous to how the Taylor series represents a function in terms of its derivativesWe axiomatize the method using the axioms that axiomatize the Shapley value—linearity,dummyandefficiency—and also an additional axiom that we call theinteraction distributionaxiom. This axiom explicitlycharacterizes how interactions are distributed for a class of games called interaction games.We contrast Shapley-Taylor values against the previously proposed Shapley Interaction Value(cf. [1]) thatinstead relies on a recursive construction rather than the efficiency and interaction distribution axioms.
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We analyze state-of-the-art deep learning
models for three tasks: question answering
on (1) images, (2) tables, and (3) passages
of text. Using the notion of attribution
(word importance), we find that
these deep networks often ignore important
question terms. Leveraging such behavior,
we perturb questions to craft a variety
of adversarial examples. Our strongest
attacks drop the accuracy of a visual question
answering model from 61.1% to 19%,
and that of a tabular question answering
model from 33.5% to 3.3%. Additionally,
we show how attributions can strengthen
attacks proposed by Jia and Liang (2017)
on paragraph comprehension models. Our
results demonstrate that attributions can
augment standard measures of accuracy
and empower investigation of model performance.
When a model is accurate but
for the wrong reasons, attributions can surface
erroneous logic in the model that indicates
inadequacies in the test data.
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Analyza: Exploring Data with Conversation
Kevin McCurley
Ralfi Nahmias
Intelligent User Interfaces 2017, ACM, Limassol, Cyprus (to appear)
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We describe Analyza, a system that helps lay users explore
data. Analyza has been used within two large real world systems. The
first is a question-and-answer feature in a spreadsheet product. The
second provides convenient access to a revenue/inventory database
for a large sales force. Both user bases consist of users who do not
necessarily have coding skills, demonstrating Analyza's ability to
democratize access to data.
We discuss the key design decisions in implementing this system.
For instance, how to mix structured and natural language modalities,
how to use conversation to disambiguate and simplify querying, how
to rely on the ``semantics'' of the data to compensate for the lack
of syntactic structure, and how to efficiently curate the data.
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A scheme that publishes aggregate information about sensitive data must resolve the trade-off between utility to information consumers and privacy of the database participants. Differential privacy is a well-established definition of privacy--this is a universal guarantee against all attackers, whatever their side-information or intent. Can we have a similar universal guarantee for utility?
There are two standard models of utility considered in decision theory: Bayesian and minimax. Ghosh et. al. show that a certain "geometric mechanism" gives optimal utility to all Bayesian information consumers. In this paper, we prove a similar result for minimax information consumers. Our result also works for a wider class of information consumers which includes Bayesian information consumers and subsumes the result from [8].
We model information consumers as minimax (risk-averse) agents, each endowed with a loss-function which models their tolerance to inaccuracies and each possessing some side-information about the query. Further, information consumers are rational in the sense that they actively combine information from the mechanism with their side-information in a way that minimizes their loss. Under this assumption of rational behavior, we show that for every fixed count query, the geometric mechanism is universally optimal for all minimax information consumers.
Additionally, our solution makes it possible to release query results, when information consumers are at different levels of privacy, in a collusion-resistant manner.
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