Minimax experimental design: Bridging the gap between statistical and worst-case approaches to least-squares regression
Abstract
In experimental design, we are given a large collection of vectors, each with a hidden response
value that we assume derives from an underlying linear model, and we wish to pick a small subset
of the vectors such that querying the corresponding responses will lead to a good estimator of the
model. A classical approach in statistics is to assume the responses are linear, plus zero-mean
i.i.d. Gaussian noise, in which case the goal is to provide an unbiased estimator with smallest mean
squared error (A-optimal design). A related approach, more common in computer science, is to
assume the responses are arbitrary but fixed, in which case the goal is to estimate the least squares
solution using few responses, as quickly as possible, for worst-case inputs. Despite many attempts,
characterizing the relationship between these two approaches has proven elusive. We address this
by proposing a framework for experimental design where the responses are produced by an arbitrary
unknown distribution. We show that there is an efficient randomized experimental design procedure
that achieves strong variance bounds for an unbiased estimator using few responses in this general
model. Nearly tight bounds for the classical A-optimality criterion, as well as improved bounds
for worst-case responses, emerge as special cases of this result. In the process, we develop a
new algorithm for a joint sampling distribution called volume sampling, and we propose a new
i.i.d. importance sampling method: inverse score sampling. A key novelty of our analysis is in
developing new expected error bounds for worst-case regression by controlling the tail behavior
of i.i.d. sampling via the jointness of volume sampling. Our result motivates a new minimaxoptimality criterion for experimental design which can be viewed as an extension of both A-optimal
design and sampling for worst-case regression.
Research Areas
