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<article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" article-type="research-article">
<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">JDS</journal-id>
<journal-title-group><journal-title>Journal of Data Science</journal-title></journal-title-group>
<issn pub-type="epub">1683-8602</issn><issn pub-type="ppub">1680-743X</issn><issn-l>1680-743X</issn-l>
<publisher>
<publisher-name>School of Statistics, Renmin University of China</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="publisher-id">JDS1212</article-id>
<article-id pub-id-type="doi">10.6339/25-JDS1212</article-id>
<article-categories><subj-group subj-group-type="heading">
<subject>Statistical Data Science</subject></subj-group></article-categories>
<title-group>
<article-title>Explainable Machine Learning for Functional Data</article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name><surname>Goode</surname><given-names>Katherine</given-names></name><email xlink:href="mailto:kjgoode@sandia.gov">kjgoode@sandia.gov</email><xref ref-type="aff" rid="j_jds1212_aff_001">1</xref><xref ref-type="corresp" rid="cor1">∗</xref>
</contrib>
<contrib contrib-type="author">
<name><surname>Tucker</surname><given-names>J. Derek</given-names></name><xref ref-type="aff" rid="j_jds1212_aff_001">1</xref>
</contrib>
<contrib contrib-type="author">
<name><surname>Ries</surname><given-names>Daniel</given-names></name><xref ref-type="aff" rid="j_jds1212_aff_001">1</xref>
</contrib>
<contrib contrib-type="author">
<name><surname>Hofmann</surname><given-names>Heike</given-names></name><xref ref-type="aff" rid="j_jds1212_aff_002">2</xref>
</contrib>
<aff id="j_jds1212_aff_001"><label>1</label><institution>Sandia National Laboratories</institution>, Albuquerque, NM, <country>United States</country></aff>
<aff id="j_jds1212_aff_002"><label>2</label>Department of Statistics, <institution>University of Nebraska-Lincoln</institution>, Lincoln, NE, <country>United States</country></aff>
</contrib-group>
<author-notes>
<corresp id="cor1"><label>∗</label>Corresponding author. Email: <ext-link ext-link-type="uri" xlink:href="mailto:kjgoode@sandia.gov">kjgoode@sandia.gov</ext-link>.</corresp>
</author-notes>
<pub-date pub-type="ppub"><year>2026</year></pub-date><pub-date pub-type="epub"><day>16</day><month>12</month><year>2025</year></pub-date><volume>24</volume><issue>1</issue><fpage>125</fpage><lpage>145</lpage><supplementary-material id="S1" content-type="archive" xlink:href="jds1212_s001.zip" mimetype="application" mime-subtype="x-zip-compressed">
<caption>
<title>Supplementary Material</title>
<p>The supplementary materials include additional analyses on the shifted peaks, H-CT, and inkjet printer data, implementation details, R and Python code, and the shifted peaks and inkjet datasets. Due to proprietary reasons, the H-CT dataset is not able to be shared.</p>
</caption>
</supplementary-material><history><date date-type="received"><day>27</day><month>3</month><year>2025</year></date><date date-type="accepted"><day>8</day><month>12</month><year>2025</year></date></history>
<permissions><copyright-statement>2026 The Author(s). Published by the School of Statistics and the Center for Applied Statistics, Renmin University of China.</copyright-statement><copyright-year>2026</copyright-year>
<license license-type="open-access" xlink:href="https://creativecommons.org/licenses/by/4.0/">
<license-p>Open access article under the <ext-link ext-link-type="uri" xlink:href="https://creativecommons.org/licenses/by/4.0/">CC BY</ext-link> license.</license-p></license></permissions>
<abstract>
<p>Black-box machine learning models are recognized as useful tools for prediction applications, but the algorithmic complexity of some models causes interpretation challenges. Explainability methods have been proposed to provide insight into these models, but there is little research focused on supervised modeling with functional data inputs. We argue that, especially in applications of high consequence, it is important to explicitly model the functional dependence in a black-box analysis to not obscure or misrepresent patterns in explanations. As such, we propose the <italic><bold>V</bold>ariable importance <bold>E</bold>xplainable <bold>E</bold>lastic <bold>S</bold>hape <bold>A</bold>nalysis (VEESA) pipeline</italic> for training supervised machine learning models with functional inputs. The pipeline is an analysis process that includes the data preprocessing, modeling, and post-hoc explanations. The preprocessing is done using elastic functional principal components analysis, which accounts for vertical and horizontal variability in functional data and, ultimately, allows for explanations in the original data space that identify the important functional variability without bias due to correlated variables. Here, we demonstrate the pipeline on two high-consequence applications: explosives classification for national security and inkjet printer identification in forensic science. The applications exhibit the VEESA pipeline’s ability to provide an understanding of the characteristics of the functional data useful for prediction. Code for implementing the pipeline is available in the <italic>veesa</italic> R package (and supplemental python code).</p>
</abstract>
<kwd-group>
<label>Keywords</label>
<kwd>elastic shape analysis</kwd>
<kwd>explainability</kwd>
<kwd>functional principal components</kwd>
<kwd>interpretability</kwd>
<kwd>variable importance</kwd>
</kwd-group>
<funding-group><funding-statement>Sandia National Laboratories is a multimission laboratory managed and operated by National Technology &amp; Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.</funding-statement></funding-group>
</article-meta>
</front>
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