1# RECORD 549587ac03dcb9d550c7fe68da027277dd876b122# TITLE: A divide-and-conquer approach for spatio-temporal analysis of large house price data from Greater London3# YEAR: 2024.0 VENUE: Annals of Operations Research DOI: 10.1007/s10479-025-06889-x4# AUTHORS: Kapil Gupta; Soudeep Deb5# PAGES: 27 CANDIDATE TABLE PAGES (1-based): [8, 9, 11, 14, 17, 19, 23]6# ABSTRACT: Recent statistical research in real estate markets focuses on the spatio-temporal dynamics of house prices. Bayesian methods are common but often slow for a large dataset in that regard. We propose a divide-and-conquer (D&C) approach, partitioning the data into subsets and applying Gaussian process models in parallel. The results are combined using the Wasserstein barycenter technique to obtain global parameters. This method allows for multiple observations per spatial and time unit. As a real-life application, we analyze house price data of more than 0.6 million transactions from 983 middle layer super output areas in London over a period of eight years. A couple of our major findings is that different types of property command different levels of premiums across the region; and that lower carbon emissions correlate positively with house prices, though the magnitude of this premium has diminished over recent years. Overall, our proposed model offers a better fit than competing approaches, attaining the highest \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R^2$$\end{document} (0.796) and lowest root mean squared error (0.211). Specifically, it improves the error by approximately 50% compared to traditional hedonic and temporal models, while achieving improvements of 28% over fixed-effects model, and improvement of 12% over a spatial model. Most importantly, the D&C spatial variant achieves a 40-fold computational speed-up with minimal accuracy reduction. For unobserved properties, predictions remain highly reliable, achieving a mean absolute percentage error below 10% in over 98% of cases.789===== PAGE 1 (score 8, numeric-paren 0, table-words 1, var-words 6) =====1011A divide-and-conquer approach for spatio-temporal analysis of large house price12data from Greater London13Kapil Gupta, Soudeep Deb14Indian Institute of Management Bangalore15Bannerghatta Main Road, Bangalore, Karnataka 560076, India.16Abstract17Statistical research in real estate markets, particularly in understanding the spatio-temporal dynamics18of house prices, has garnered significant attention in recent times. Although Bayesian methods are19common in spatio-temporal modeling, standard Markov chain Monte Carlo (MCMC) techniques are20usually slow for large datasets such as house price data. To tackle this problem, we propose a divide-21and-conquer spatio-temporal modeling approach.22This method involves partitioning the data into23multiple subsets and applying an appropriate Gaussian process model to each subset in parallel. The24results from each subset are then combined using the Wasserstein barycenter technique to obtain the25global parameters for the original problem. The proposed methodology allows for multiple observations26per spatial and time unit, thereby offering added benefits for practitioners. As a real-life application,27we analyze house price data of more than 0.6 million transactions from 983 middle layer super output28areas in London over a period of eight years. The methodology provides insightful findings about the29effects of various amenities, trend patterns, and the relationship between prices and carbon emissions.30Furthermore, as demonstrated through a cross-validation study, it shows good predictive accuracy31while balancing computational efficiency.32Keywords:33Bayesian analysis, Real estate, Space-time prediction, Wasserstein barycenter341. Introduction35The valuation of residential properties is immensely important for various economic stakeholders,36including property dealers, sellers, and buyers. Traditionally, house price modeling has revolved around37the hedonic framework (Rosen, 1974).38Specifically, log-linear regression techniques have been at39the forefront in the analysis of house price transactions (Liu, 2013). However, the incorporation of40location attributes into the mean structure of hedonic regression, as recommended by Dubin and Sung41(1990), has shown limitations in capturing all significant neighborhood attributes, potentially giving42rise to spatial autocorrelation concerns. To overcome this challenge, researchers have advocated for the43inclusion of spatial effects into the error structure (Can, 1990; Pace and Gilley, 1998). Simultaneously,44the dynamics of house prices are profoundly influenced by temporal autocorrelation as well.45Pace46et al. (1998) leveraged the concepts of spatio-temporal modeling to comprehensively capture both47spatial and temporal effects within house price data.48This modeling approach has since become49a cornerstone in academic research. Building on this foundation, Liu (2013) harnessed the spatio-50temporal autoregressive (STAR) model to address correlated errors in traditional hedonic regression,51delving into spatial and temporal dependence considerations and further developing a house price52index as a pivotal part of their analysis. Interestingly, their methodology assumed the spatial weight53matrix to be lower triangular, which implies that two spatial units cannot mutually influence each54other. A different approach was taken by Fotheringham et al. (2003) who integrated geographically55weighted regression with time series forecasting techniques to capture the spatio-temporal variations56arXiv:2407.15905v1 [stat.AP] 22 Jul 2024575859===== PAGE 8 (score 7, numeric-paren 4, table-words 0, var-words 3) =====6061a separable structure for the spatial dependence and the temporal dependence. In other words, it is62written as a product of purely spatial and purely temporal covariance functions:63Cov {v(si, tu), v(sj, tv)} = σ264vρs (∥si −sj∥; ϕs) ρt (∥tu −tv∥; ϕt) .65(3.4)66The separable covariance structure is favored as it significantly reduces the parameters in the67covariance matrix, and is a popular choice in similar spatio-temporal studies (see, e.g., Sahu et al.,682010; Deb and Tsay, 2019). For both spatial and temporal covariance functions, we consider the Matérn69structure with the specific choice of ν = 0.5, resulting in the exponentially decaying pattern. Thus, we70have:71ρs (∥si −sj∥; ϕs) = exp (−ϕs ∥si −sj∥) ;72ρt (∥tu −tv∥; ϕt) = exp (−ϕt ∥tu −tv∥) ,73(3.5)74where ∥tu −tv∥represents the absolute time difference, and ∥si −sj∥is calculated via the Vincenty75Ellipsoid method, which computes the great circle distance on an ellipsoid. The latter is chosen for its76superior accuracy compared to other approaches (Hijmans, 2021). It is critical to note that, because77of the separability assumption imposed on the joint covariance function, we can write the covariance78matrix Σ = σ279v (Σs ⊗Σt), where ⊗denotes the Kronecker product, and Σs, Σt respectively denote the80spatial and temporal correlation matrices, with81(Σs)ij = exp (−ϕs ∥si −sj∥) ;82(Σt)uv = exp (−ϕt ∥tu −tv∥) .83(3.6)843.2. Prior Specifications85Let θ = (β⊤, σ286v, σ287ϵ , ϕs, ϕt)⊤be the vector of unknown parameters. We estimate them completely88within a Bayesian framework, primarily using Gibbs sampling (?), for which suitable prior specifications89are essential.90For all coefficients in β, we consider independent Gaussian priors with mean 0 and91variance c, where c is relatively large, typically on the order of 104. For the error variances σ292ϵ and93σ294v, we employ independent inverse gamma priors IG(a, λ), where a and λ are the shape and scale95parameters, respectively. We choose a = 2, making these priors non-informative. We also noticed that96the parameter estimates and model selection criteria are insensitive to the initial values of the scale97parameter, and throughout this study, we take λ = 1.98For estimating the decay parameters ϕ = (ϕs, ϕt) in the covariance functions, many prior studies99(e.g., Sahu et al., 2006; ?) have used cross-validation to find the optimal choices. Albeit this approach100is computationally more tractable, it has some limitations, as it explores a small set of values and101can miss viable solutions. An alternative is the single-variable slice sampling algorithm (Neal, 2003),102which provides direct estimation of the parameters within a Bayesian framework. While this method103thoroughly explores the parameter space, it demands extensive computation as the covariance matrix104must be recalculated and inverted in every iteration of the Bayesian computation.105Keeping the106advantages of both approaches in view, we aim to achieve a middle ground – somewhat like a discrete107slice sampling – wherein a discretized sample space is considered for the parameters (ϕs, ϕt), and the108parameters are estimated directly within the Bayesian setting. This approach allows us to provide109credible intervals for these parameters. In terms of the prior specifications, we adopt a discretized110uniform prior for ϕs, selecting values from 1 to 3 in intervals of 0.2, resulting in the set As. For ϕt,111similarly, we select equidistant points between 0.2 and 1 in intervals of 0.2, and denote it as At. Below,112the product As × At is indicated as Ast, while U indicates the mentioned uniform distribution.113As mentioned before, we use concepts of Gibbs sampling and discrete slice sampling to implement114the proposed model for estimation and prediction purposes. As the first step, following Section 3.1, we115can write the full model as116Y | θ, V ∼NN117