In Response to Wilderness Search Strategy and Tactics, by Phillips et al

Abstract

We are writing regarding a recently published Concepts article, titled “Wilderness Search Strategy and Tactics.”1Phillips K. Longden M.J. Vandergraff B. et al.Wilderness search strategy and tactics.Wilderness Environ Med. 2014; 25: 166-176Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar Although we have great respect for the authors and their work, we would like to highlight where some of the content of the article deviates from the scientific literature, and US-accepted practices, regarding search theory and its application to land search. Even though the article includes the disclaimer, “The views expressed in this paper…do not necessarily reflect the views of the National Park Service,” the current and former positions of some of the authors, and the fact that the example search used throughout the article is set in a National Park (Yosemite), strongly suggest that the methodology described reflects current National Park Service (NPS) policies and procedures for conducting searches. Unfortunately, several details in the article deviate from the methodology described in the 2011 Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual (LSA),2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar a document to which the US Department of the Interior (including the NPS) is a signatory party. Our intention is to bring to the attention of the WEM readership differences between the methodology described in the article and current accepted US land search methodology.1.The article suggests that the general search area be divided into “manageable units” (segments) based on characteristics of the intended resources and how to search, not factors implying where the subject is more or less likely to be.1Phillips K. Longden M.J. Vandergraff B. et al.Wilderness search strategy and tactics.Wilderness Environ Med. 2014; 25: 166-176Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar(p173) These factors are considered only after segments have been established and “each segment is assigned a value representing ‘probability of area.’”1Phillips K. Longden M.J. Vandergraff B. et al.Wilderness search strategy and tactics.Wilderness Environ Med. 2014; 25: 166-176Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar(p173) That is, the article suggests that decisions on how and where to search are made before any evaluation of where the subject is more or less likely to be located. This approach does not reflect the current state of search methods in the United States, which are included in the LSA.2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar Specifically, this approach does not include consideration of regions of probability,2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar(p5–10) proportional methods for estimating probability of containment (POC)/probability of area (POA)2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar(p5–39), and much more. In short, the methodology suggested in the article should not conflict with the LSA, which represents the standard of care regarding search in the United States and has been accepted by all federal agencies including the National Park Service.2.The “O’Connor method”1Phillips K. Longden M.J. Vandergraff B. et al.Wilderness search strategy and tactics.Wilderness Environ Med. 2014; 25: 166-176Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar(p174) establishes initial POA values starting with letters or numbers and eventually converting them to percentages. This method does not maintain proportionality, which is required by search theory and the LSA2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar(p5–39), and therefore is not an acceptable method of establishing initial POA values.5Cooper D.C. Frost J.R. Robe R.Q. Compatibility of Land SAR Procedures With Search Theory.Prepared for US Department of Homeland Security, US Coast Guard, Operations (G-OPR), Contract DTCG39-00-D-R00009, Task Order DTCG32-02-F-000032. Potomac Management Group, Inc, Washington, DC2003Google Scholar(pp81–84)3.The article suggests that “The segments with the higher POA values then receive higher search priority.”1Phillips K. Longden M.J. Vandergraff B. et al.Wilderness search strategy and tactics.Wilderness Environ Med. 2014; 25: 166-176Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar(p174) Koester3Koester R.J. Lost Person Behavior.A Search and Rescue Guide on Where to Look—for Land, Air, and Water. dBS Productions, Charlottesville, VA2008Google Scholar(p316) is cited, but nothing on the page of the reference cited—or within the entire reference—describes managing a search in this way. The end of the article also appears to suggest that segments be searched in order of highest to lowest POA.1Phillips K. Longden M.J. Vandergraff B. et al.Wilderness search strategy and tactics.Wilderness Environ Med. 2014; 25: 166-176Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar(p175) Searching segments in this order has no basis in search theory,5Cooper D.C. Frost J.R. Robe R.Q. Compatibility of Land SAR Procedures With Search Theory.Prepared for US Department of Homeland Security, US Coast Guard, Operations (G-OPR), Contract DTCG39-00-D-R00009, Task Order DTCG32-02-F-000032. Potomac Management Group, Inc, Washington, DC2003Google Scholar(p46),9Frost J.R. Principles of search theory, parts III and IV: probability density distributions and optimal effort allocation.Response. 1999; 17: 16-23Google Scholar is in conflict with the methodology described in the LSA,2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar(part5) will often give far less than optimal results in terms of probability of success (POS) per unit of time,2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar(section5–7),9Frost J.R. Principles of search theory, parts III and IV: probability density distributions and optimal effort allocation.Response. 1999; 17: 16-23Google Scholar and should be discarded.5Cooper D.C. Frost J.R. Robe R.Q. Compatibility of Land SAR Procedures With Search Theory.Prepared for US Department of Homeland Security, US Coast Guard, Operations (G-OPR), Contract DTCG39-00-D-R00009, Task Order DTCG32-02-F-000032. Potomac Management Group, Inc, Washington, DC2003Google Scholar(pp98–99)4.The article suggests that the “rest of the world” (ROW) be assigned a POA value.1Phillips K. Longden M.J. Vandergraff B. et al.Wilderness search strategy and tactics.Wilderness Environ Med. 2014; 25: 166-176Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar(p174) That is in conflict with search theory and the LSA,2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar and appears to resurrect an old method of using POA in an inappropriate way secondary to a lack of full understanding of POS and its use.5Cooper D.C. Frost J.R. Robe R.Q. Compatibility of Land SAR Procedures With Search Theory.Prepared for US Department of Homeland Security, US Coast Guard, Operations (G-OPR), Contract DTCG39-00-D-R00009, Task Order DTCG32-02-F-000032. Potomac Management Group, Inc, Washington, DC2003Google Scholar(pp81–84)5.The article’s use of “coverage”1Phillips K. Longden M.J. Vandergraff B. et al.Wilderness search strategy and tactics.Wilderness Environ Med. 2014; 25: 166-176Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar(p174) is in direct conflict with the definition and use of the same term in both the LSA and the scientific search theory literature. Coverage (also know as “coverage factor”) is defined in the LSA, and in many other sources, as “the ratio of ‘area effectively swept’ (ie, the product of effective sweep width and total track line length [TTLL]) to the physical area that was searched.” 2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar(p5–13),5Cooper D.C. Frost J.R. Robe R.Q. Compatibility of Land SAR Procedures With Search Theory.Prepared for US Department of Homeland Security, US Coast Guard, Operations (G-OPR), Contract DTCG39-00-D-R00009, Task Order DTCG32-02-F-000032. Potomac Management Group, Inc, Washington, DC2003Google Scholar, 6Koopman B.O. Search and Screening: General Principles With Historical Applications. Pergamon Press, New York, NY1980Google Scholar, 7Stone LD. Theory of Optimal Search. 2nd ed. Military Applications Section, Operations Research Society of America. Arlington, VA: ORSA Books. Now available through Institute for Management Science and Operations Research, Catonsville, MD. Available at: https://www.informs.org/pubs/topics-in-or/book-list/theory-of-optimal-search.Google Scholar, 8Frost J.R. Principles of search theory, parts I and II: detection, effort, coverage, and POD.Response. 1999; 17: 1-15Google Scholar, 9Frost J.R. Principles of search theory, parts III and IV: probability density distributions and optimal effort allocation.Response. 1999; 17: 16-23Google Scholar6.The article describes probability of detection (POD) as “…a value representing the searchers’ confidence in their search area coverage…” that is “subjectively determined.”1Phillips K. Longden M.J. Vandergraff B. et al.Wilderness search strategy and tactics.Wilderness Environ Med. 2014; 25: 166-176Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar(p174) It then defines POD as “the chance of locating the subject in a given area during a given search effort (eg, ‘I had a 10% chance of finding the subject’).”1Phillips K. Longden M.J. Vandergraff B. et al.Wilderness search strategy and tactics.Wilderness Environ Med. 2014; 25: 166-176Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar(p174) This definition is incorrect. As per the LSA and the scholarly literature on which it is based, POD is the conditional probability of detecting the search object if it is in the area (segment) searched at the time of the search.2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar(p5–11),4Koester R.J. Cooper D.C. Frost J.R. Robe R.Q. Sweep Width Estimate for Ground Search and Rescue.Prepared for US Department of Homeland Security, US Coast Guard, Operations (G-OPR), Contract DTCG32-02-D-R00010, Task Order DTCG32-03-F000012. Potomac Management Group, Inc, Washington, DC2004Google Scholar(p15),6Koopman B.O. Search and Screening: General Principles With Historical Applications. Pergamon Press, New York, NY1980Google Scholar, 8Frost J.R. Principles of search theory, parts I and II: detection, effort, coverage, and POD.Response. 1999; 17: 1-15Google Scholar The POD is a function of coverage (C), which is in turn a function of the effective sweep width, effort (TTLL) expended in the area (segment), and the physical size (area) of the segment searched.2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar(p5–13),4Koester R.J. Cooper D.C. Frost J.R. Robe R.Q. Sweep Width Estimate for Ground Search and Rescue.Prepared for US Department of Homeland Security, US Coast Guard, Operations (G-OPR), Contract DTCG32-02-D-R00010, Task Order DTCG32-03-F000012. Potomac Management Group, Inc, Washington, DC2004Google Scholar(pp8–16),6Koopman B.O. Search and Screening: General Principles With Historical Applications. Pergamon Press, New York, NY1980Google Scholar, 8Frost J.R. Principles of search theory, parts I and II: detection, effort, coverage, and POD.Response. 1999; 17: 1-15Google Scholar Therefore, it is an objective, not a subjective, estimate. In addition, formal detection experiments performed in 2003 and 2004 showed zero correlation between searcher estimates of POD and their actual detection performance.4Koester R.J. Cooper D.C. Frost J.R. Robe R.Q. Sweep Width Estimate for Ground Search and Rescue.Prepared for US Department of Homeland Security, US Coast Guard, Operations (G-OPR), Contract DTCG32-02-D-R00010, Task Order DTCG32-03-F000012. Potomac Management Group, Inc, Washington, DC2004Google Scholar(pp127–129) Therefore, POD values based on polling the searchers themselves are of no value at best, and extremely misleading at worst.7.The paper describes an “inherent subjectivity in this process” and suggests that “search professionals have researched techniques that will derive more accurate and objective values representing coverage.”1Phillips K. Longden M.J. Vandergraff B. et al.Wilderness search strategy and tactics.Wilderness Environ Med. 2014; 25: 166-176Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar(p174) It goes on to suggest that “critical separation” and subjective estimates of detection from searchers can be somehow combined to result in POD.1Phillips K. Longden M.J. Vandergraff B. et al.Wilderness search strategy and tactics.Wilderness Environ Med. 2014; 25: 166-176Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar(p174) That is incorrect. So-called “critical separation” does not provide an estimate of effective sweep width, which is required to compute POD. In addition, the subjective approach to directly estimating POD has been removed from most of the land search and rescue (SAR) literature for more than a decade because it is no longer an accepted best practice for computing POD in land search. This approach is also in conflict with the method of computing POD described in the LSA.2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar, 5Cooper D.C. Frost J.R. Robe R.Q. Compatibility of Land SAR Procedures With Search Theory.Prepared for US Department of Homeland Security, US Coast Guard, Operations (G-OPR), Contract DTCG39-00-D-R00009, Task Order DTCG32-02-F-000032. Potomac Management Group, Inc, Washington, DC2003Google Scholar(pp5–15)8.The article’s description of global positioning satellite (GPS) tracking and its use1Phillips K. Longden M.J. Vandergraff B. et al.Wilderness search strategy and tactics.Wilderness Environ Med. 2014; 25: 166-176Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar(pp174–175) suggests a lack of understanding of POD and effective sweep width, and is inconsistent with the methodology described in the LSA.2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar What appears to be completely lacking, and perhaps misunderstood, is effective sweep width, a common oversight in land SAR in decades past.5Cooper D.C. Frost J.R. Robe R.Q. Compatibility of Land SAR Procedures With Search Theory.Prepared for US Department of Homeland Security, US Coast Guard, Operations (G-OPR), Contract DTCG39-00-D-R00009, Task Order DTCG32-02-F-000032. Potomac Management Group, Inc, Washington, DC2003Google Scholar Fortunately, land SAR has evolved in the past 10 years to incorporate these concepts in its best practices, and these practices are described in the LSA.2US National Search and Rescue Committee (NSARC).Land Search and Rescue Addendum to the National Search and Rescue Supplement to the International Aeronautical and Maritime Search and Rescue Manual, Version 1.0.. US National Search and Rescue Committee, Washington, DC2011Google Scholar Wilderness Search Strategy and TacticsWilderness & Environmental MedicineVol. 25Issue 2PreviewReports of overdue persons are common for search and rescue personnel. Search incidents for missing persons are conducted following established industry standard practices, which are continuously refined through experience and the analysis of previous search operations. Throughout this process, elements of uncertainty exist, and the knowledge and experience of the searchers and search managers may influence the outcome significantly. A sound knowledge of current search tactics will help search and rescue medical providers function more effectively during search operations. Full-Text PDF Reply to “In Response to Wilderness Search Strategy and Tactics”Wilderness & Environmental MedicineVol. 26Issue 2PreviewWe would like to thank Dr Cooper and Mr Frost for their comments1 regarding our recent article “Wilderness Search Strategy and Tactics.”2 Their experience and points provide an excellent complementary perspective. We would like to point out that the intent of our article was to summarize current search strategies in a manner that would illustrate the basics of search strategy to medical providers and readers with no background in search management. It was not intended to be a treatise on land search techniques. Full-Text PDF