OSAC 2023-S-0017 Standard for the Articulation of 

Footwear and Tire Interpretations

1

OSAC 2023-S-0017 

Standard for the 

Articulation of Footwear 

and Tire Interpretations 

Footwear/Tire Subcommittee

Pattern/Physics SAC

Organization of Scientific Area Committees (OSAC) for Forensic Science
OSAC 2023-S-0017 Standard for the Articulation of 

Footwear and Tire Interpretations

2

Draft OSAC Proposed Standard

OSAC 2023-S-0017 Standard for the 

Articulation of Footwear and Tire 

Interpretations

Prepared by 

Footwear/Tire Subcommittee

Version: 1.0

June 2023

Disclaimer:

This OSAC Proposed Standard was written by the Organization of Scientific Area Committees (OSAC) 

for Forensic Science following a process that includes an open comment period. This Proposed Standard 

will be submitted to a standards developing organization and is subject to change.

There may be references in an OSAC Proposed Standard to other publications under development by 

OSAC. The information in the Proposed Standard, and underlying concepts and methodologies, may be 

used by the forensic-science community before the completion of such companion publications.

Any identification of commercial equipment, instruments, or materials in the Proposed Standard is not a 

recommendation or endorsement by the U.S. Government and does not imply that the equipment, 

instruments, or materials are necessarily the best available for the purpose.

To be placed on the OSAC Registry, certain types of standards first must be reviewed by a Scientific and 

Technical Review (STR). The STR process is vital to OSAC’s mission of generating and recognizing 

scientifically sound standards for producing and interpreting forensic science results. The STR shall 

provide critical and knowledgeable reviews of draft standards or of proposed revisions of standards 

previously published by standards developing organizations (SDOs) to ensure that the published methods 

that practitioners employ are scientifically valid, and the resulting claims are trustworthy.

The STR will consist of an independent and diverse panel, including subject matter experts, human 

factors scientists, quality assurance personnel, and legal experts, which will be tasked with evaluating the 

proposed standard based on a comprehensive list of science-based criteria.

For more information about this important process, please visit our website 

at: https://www.nist.gov/topics/organization-scientific-area-committees-forensic-science/scientifictechnical-review-panels. 

Keywords: footwear, tire, impression, evidence, articulation, interpretations
OSAC 2023-S-0017 Standard for the Articulation of 

Footwear and Tire Interpretations

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1 Foreword

2 This document outlines a standard framework for articulating source opinions for the 

3 forensic footwear/tire discipline. This standard describes necessary comparative 

4 observations and interpretations and provides a model for articulating qualitative source 

5 opinions using an evaluative reporting approach.

6

7 This document has been developed by the Footwear and Tire Subcommittee of the 

8 Organization of Scientific Area Committees for Forensic Science through a consensus process 

9 and is being proposed for further development through a Standard Developing Organization 

10 (SDO). This document was developed with input from experts with a broad array of subject 

11 matter expertise, including forensic practitioners, scientific researchers, measurement 

12 scientists, statisticians, and legal experts.

13 All hyperlinks and web addresses shown in this document are current as of the publication 

14 date of this standard.

15

16

17

18
OSAC 2023-S-0017 Standard for the Articulation of 

Footwear and Tire Interpretations

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19 TABLE OF CONTENTS

20 1 2

21 2 3

22 3 5

23 3.1 5

24 3.2 5

25 4 5

26 4.1 6

27 4.2 7

28 4.3 8

29 4.4 9

30 4.5 10

31 4.6 11

32 5 12

33 6 13

34

35

36
OSAC 2023-S-0017 Standard for the Articulation of 

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37 1 Scope

38 This standard provides a framework for a justifiable, transparent, and understandable 

39 means of articulating results/interpretations in the footwear/tire evidence discipline. This 

40 standard defines terms, describes comparative observations and interpretations of data, and 

41 establishes model qualitative articulations for the range of results/interpretations that may 

42 be reached following footwear/tire evidence comparisons. For the purpose of this standard, 

43 results/interpretations are defined as expert opinions based on the questioned impression, 

44 known items, direct observations, and any other task relevant information. The 

45 results/interpretations are derived using acquired knowledge, training, skills, and 

46 experience of the footwear/tire evidence examiner.

47 This standard does not cover the following topics:

48 ● Results/interpretations derived directly from and/or entirely dependent upon 

49 validated probability models or quantitative processes.

50 ● Determination of the relevant population for evaluation.

51 ● Detailed guidelines for documentation of comparisons and results/interpretations.

52 ● Detailed guidelines for reporting and testifying.

53 ● Results/interpretations in which an examiner is assessing the type or categorization of 

54 a single item. 

55 ● Results/interpretations in which an examiner is comparing two questioned 

56 impressions to each other (without known footwear/tire).

57 ● Results/interpretations in which an examiner is assessing the events or activities that 

58 produced the given evidence. 

59 ● Validation or verification of these results/interpretations.

60 2 Terminology 

Key terms used in this document include the following1 61 :

62 ● Source opinions are those opinions in which an examiner is assessing the degree to 

63 which the evidence supports whether two (or more) items came from the same source 

64 versus different sources (e.g., whether two footwear impressions came from the same 

65 item of footwear) OR whether one (or more) items came from a specified source (e.g., 

66 whether a tire impression came from a known tire or a different tire).

67 ● Item of evidence (“item”) refers to the object, sample, image, impression, or document 

68 being examined. Items may be from unknown or known sources.

69 ● Source refers to a specific object (e.g., a shoe, or a tire).

70 ● Observation: recognizing and noting an occurrence. For the purpose of this document, 

71 “occurrence” refers to features, attributes, and/or measurements.

1 Additional relevant terminology can be found in the most recent version of the document entitled “Terminology 

Used for Forensic Footwear and Tire Evidence (as of this writing, this is ASB Technical Report 097, First Edition 

(2019) as well as in the OSAC Lexicon (https://lexicon.forensicosac.org). Unless specified otherwise, definitions 

included in this document supercede those in other documents for the purposes of this standard.
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Footwear and Tire Interpretations

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72 ● Articulation: communication or explanation of the entire examination and decision73 making process to encompass observations and interpretations

74 ● Characteristics of Use: features that are acquired through the wearing/usage of shoes 

75 and tires, to include general wear, specific wear, Schallamach, and randomly acquired 

76 characteristics (RACs)

77 ● Specific characteristics of use: a subcategory of “characteristics of use” to encompass 

78 only non-class characteristics (i.e., those characteristics with higher discriminability), 

79 including specific wear and RACs

80 ● Similarity (similar): an observation that an impression and a footwear outsole or tire 

81 track share a likeness of details; not to be confused with correspondence.

82 ● Dissimilarity (dissimilar): an observation that characteristics have the appearance of 

83 being potentially different but do not meet the criteria for an exclusionary difference. 

84 This observation could be caused by numerous factors including but not limited to the 

85 impression-making process, factors prior to recovery, and/or the recovery process.

86 ● Correspondence: an interpretation that observed similarities between one or more 

87 features or properties between the compared items are considered to constitute 

88 agreement.

89 ● Exclusionary difference: A difference in one or more characteristics between 

90 compared items that is sufficient to determine that the compared items did not 

91 originate from the same source, are not the same source, or do not share the same 

92 composition or classification. NOTE: What is sufficient depends on the performance and 

93 limitations of the method used on the material in question.

94 ● Quality: a property of footwear and tire impressions or known images/exemplars

95 which denotes the fidelity of reproduction of the outsole or tire. This includes the 

96 accuracy and clarity of the reproduction which will determine the suitability of the 

97 evidence (or its value for comparison).

98 ● Discriminability (or distinctiveness): the degree to which information in an 

99 impression can be used to reliably distinguish between different sources. The 

100 discriminability of an impression encompasses its features’ quantity, spatial 

101 arrangement, quality, and rarity/perceived rarity.

● Measured rarity2 102 : the measured prevalence of a feature or set of features observed in 

103 evidence using representative databases, research, and/or manufacturing/distribution 

104 information. NOTE: very few (if any) such data currently exist for practical use in 

105 footwear or tire evidence. 

● Perceived rarity3 106 : an examiner’s assessment of the prevalence of a feature or set of 

107 features based upon his/her training, experience, and/or case factors, in the absence of 

108 data (as outlined under “measured rarity”). When perceived rarity is considered during 

2 Rarity (either measured or perceived) of the class characteristic of make/model and/or size of a footwear or tire 

refers to how often that type of feature is encountered in a group of footwear or tires (its prevalence), either in 

isolation or in conjunction with other information about its local context. Rarity of the location and degree of wear 

as well as the size and shape of randomly acquired characteristics refers to how frequently these types of features are 

encountered in a group of footwear or tires (their prevalence), either in isolation or in conjunction with other 

information about local context.

3 See footnote 2.
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Footwear and Tire Interpretations

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109 the decision-making process, the examiner must clearly and thoroughly describe the 

110 information considered.

111 ● Inclusion: the known footwear or tire exhibits similarities in class characteristics and/or 

112 characteristics of use that indicate the footwear/tire may have made the questioned 

113 impression and thus is part of the pool of potential sources for the questioned 

114 impression.

115 ● Exclusion: the known footwear or tire exhibits differences in class characteristics or 

116 characteristics of use that indicate the footwear/tire did not make the questioned 

117 impression and thus is NOT part of the pool of potential sources for the questioned 

118 impression.

119 ● Specific wear: wear that is more discriminable than general wear by virtue of its 

120 specific location, degree and orientation (e.g., erosion causing tears/holes, advanced 

121 wear in an atypical contact area). Specific wear also includes Schallamach patterns.

122 3 Value (Suitability) Determinations 

123 A value or suitability determination is a judgment of whether an item contains sufficient 

124 information for a comparison. 

125 3.1 Not Suitable for Comparison

126 A not suitable for comparison determination is a judgment that a more detailed 

127 examination is not warranted. The examiner determined there were minimal or no 

128 confirmable or discernable features present. This determination applies when there is 

129 insufficient detail to conduct any comparison.

130 3.2 Suitable for Comparison

131 A suitable for comparison determination is a judgment that a source opinion can potentially 

132 be reached. The examiner determined that the item contains sufficient observed data (e.g., 

133 sufficient quality and quantity of features, size, or condition of any evidence items) to be used 

134 for a comparison.

135 4 Articulation of Source Opinions

136 Source opinions apply to the comparison and evaluation of two (or more) items. In 

137 particular, these items of evidence are generally categorized as one of two types: questioned 

138 footwear/tire impressions and known footwear/tires. In reaching source opinions, an 

139 examiner evaluates the quality, quantity, and discriminability of characteristics in the 

140 evidence, the persistence of characteristics on the outsole/tread over time (if applicable), 

141 and the extent of similarities and dissimilarities of the observed characteristics, while taking 

142 into account the measured or perceived rarity of these observed characteristics and any 

143 potential limitations of the items. Potential limitations may include distortion, improper 

144 recovery methods, photographic issues, and time delay between deposition and collection.
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145 Examiners shall assess the strength of evidence by considering the prospect of encountering 

146 the observed combination of characteristics if the questioned impression came from the 

147 known footwear or tire, relative to the prospect of finding the observed combination of 

148 characteristics if the questioned impression came from a different source. The size of the 

149 pool of other potential sources is typically unknown, but can be expected to decrease as the 

150 number and type of features in correspondence increases. Examiners shall express their 

151 assessments of strength of evidence using the categories herein.

152 Examiners shall state their opinions using the full articulations below, not merely using the 

153 category labels (e.g., “support for source exclusion”), including in documentation and 

154 reporting. Examiners should provide the entire articulation scale in their documentation and 

155 reporting. Where possible, the same articulation requirements apply to testimony. In 

156 particular, examiners shall state their opinions in terms of the support for the following two 

157 propositions given their observations and interpretations of said observations: 

158 ● The support for the proposition that the known footwear/tire made the questioned 

159 impression (known source)

160 ● The support for the proposition that a different footwear/tire made the questioned 

161 impression (different source)

162 For example, an examiner might state that the observed characteristics provide strong 

163 support for the proposition that the questioned impression came from a different source and 

164 negligible support for the proposition that the questioned impression came from the known 

165 footwear/tire.

166 Figure 1 shows the articulation categories for footwear and tire interpretations. The 

167 following descriptions are meant to provide context to the levels of opinions reached in 

168 footwear and tire impression comparisons. The descriptions of each level are not intended 

169 to be all inclusive for every possible observation. Each source opinion is broken down into 

170 the required observations, the appropriate interpretations of said observations, and the 

171 necessary articulation to report the given opinion.

172

173 Figure 1. Articulation of source opinions for footwear and tire interpretations. (Note: the size of the categories are not meant to 

174 reflect the expected frequency of each opinion category or the size of the pool of potential sources)

175 4.1 Source Exclusion 

176 4.1.1 Observation

177 Significant dissimilarities were noted in the comparison of class characteristics and/or 

178 characteristics of use between the questioned impression and the known footwear or tire. 

179 4.1.2 Interpretation
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180 Source exclusion is an examiner’s opinion that the observed characteristics provide 

181 extremely strong support for the proposition that a different footwear or tire made the 

182 questioned impression and no support for the proposition that the known footwear or tire 

183 made the questioned impression. Source exclusion is only justified if the examiner’s opinion 

184 is that the prospect of finding the observed characteristics, if the two items came from the 

185 same source, is negligible.

186 Source exclusion can be expressed using absolutes if there is a logical impossibility that the 

187 items came from the same source (e.g., an outsole design composed of zig zags and circles 

188 can be definitively excluded as the source of an impression in which only square blocks are 

189 apparent). In this scenario, an opinion of source exclusion represents a posterior odds 

190 statement in which there is no support for the proposition that the known footwear or tire 

191 made the questioned impression.

192 Characteristics of use should only be used as the sole observation in forming an opinion of 

193 source exclusion if the known footwear or tire is recovered shortly after the deposition of 

194 the impression and differs significantly in the quality and quantity of characteristics of use 

195 or when the quality of the questioned impression is very high. 

196 4.1.3 Articulation

197 Sufficient exclusionary differences were noted in the comparison of class characteristics 

198 and/or characteristics of use between the questioned impression and the known footwear 

199 or tire to state that the prospect of finding the observed characteristics, if the two items came 

200 from the same source, is negligible.

201 The examiner shall explicitly detail his/her observations regarding:

202 ● The specific class characteristics and/or characteristics of use observed in the 

203 questioned impression versus the known footwear or tire

204 ● Any observed similarities between these characteristics

205 ● Any observed dissimilarities between these characteristics, why these were 

206 interpreted to be exclusionary differences, and why they were determined to be 

207 sufficiently strong to report source exclusion

208 ● Any limiting factors that were encountered during the examination and how these 

209 limitations were accounted for, evaluated, and/or mitigated

210 4.2 Support for Source Exclusion

211 4.2.1 Observation

212 The questioned impression exhibits dissimilarities in class characteristics and/or 

213 characteristics of use when compared to the known footwear or tire. 

214 4.2.2 Interpretation

215 Support for source exclusion is an examiner’s opinion that there are limitations associated 

216 with the observed characteristics or evidence (e.g., quality, quantity, availability) that 

217 prevent the examiner from reaching a stronger exclusion, but provide support for the 

218 proposition that a different footwear or tire made the questioned impression and weak 
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219 support for the proposition that the known footwear or tire made the questioned 

220 impression. 

221 An opinion of support for source exclusion may be reached if (i.) there are observed 

222 dissimilarities in class characteristics and/or characteristics of use and (ii.) one or more 

223 limiting factors, such as:

224 ● The questioned impression is partial, fragmented, or distorted

225 ● The quality of the evidence is poor or lacking (e.g., low clarity, damage to the known 

226 shoe/tire or the questioned impression, improper photographic techniques, etc.)

227 ● The time between the deposition of the impression and the recovery of the known 

228 footwear/tire may not account for the dissimilarities observed

229 ● The examiner does not have access to the known footwear/tire (and only have 

230 photographs) and/or limited test impressions

231 4.2.3 Articulation

232 The questioned impression exhibits dissimilarities when compared to the known footwear 

233 or tire and provides stronger support for the proposition that the questioned impression 

234 came from a different source than the proposition that the questioned impression came from 

235 the known footwear or tire.

236 The examiner shall explicitly detail observations and interpretations regarding:

237 ● The specific class characteristics and/or characteristics of use observed in the 

238 questioned impression versus the known footwear or tire

239 ● Any observed similarities between these characteristics

240 ● Any observed dissimilarities between these characteristics

241 ● Why any observed dissimilarities were/were not interpreted to be exclusionary 

242 differences

243 ● Why any exclusionary differences were determined to be sufficient to report 

244 support for source exclusion, but limited enough to preclude an opinion of source 

245 exclusion

246 ● Any limiting factors that were encountered during the examination and how these 

247 limitations were accounted for, evaluated, and/or mitigated

248 4.3 Indeterminate with respect to source

249 4.3.1 Observation

250 Although the evidence items were determined to be suitable for comparison, there were 

251 significant limiting factors in the questioned impression and/or known footwear or tire. 

252 These factors may include, but are not limited to: partial, fragmented or distorted 

253 impression, insufficient information, lack of scale, improper position of scale, improper 

254 photographic techniques, or significant length of time between the date of the occurrence 

255 and when the footwear or tires were recovered that could account for a different degree of 

256 general wear. 

257 4.3.2 Interpretation
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258 Indeterminate with respect to source is an examiner’s opinion that the observed 

259 characteristics are insufficient or too ambiguous to support any source opinions (as defined 

260 in the other sections). 

261 In the opinion of the examiner, there was insufficient information and/or significant limiting 

262 factors observed in the questioned impression to warrant a meaningful opinion regarding 

263 the particular known footwear outsole or tire tread. This opinion only applies to the known 

264 footwear or tire that was examined and does not necessarily preclude future examinations 

265 with other known footwear or tires.

266 4.3.3 Articulation

267 The questioned impression does not exhibit sufficient observable similarities or 

268 dissimilarities when compared to the known footwear or tire to provide support for either 

269 proposition. The observations provide relatively equivalent support for both known source

270 and different source propositions. 

271 The examiner shall explicitly detail observations and interpretations regarding:

272 ● The specific class characteristics and/or characteristics of use observed in the 

273 questioned impression

274 ● How the observed characteristics in the questioned impression compare to those 

275 observed on the known footwear or tire

276 ● Any observed similarities and/or dissimilarities between these characteristics and 

277 why these were determined to be insufficient to provide stronger support for 

278 inclusion or exclusion

279 ● Any limiting factors that were encountered during the examination

280 4.4 Support for Inclusion based on Class Characteristics

281 4.4.1 Observation

282 The class characteristics of design and physical size (if available) correspond between the 

283 questioned impression and the known footwear or tire. Correspondence of general wear (a 

284 characteristic of use) may also be observed. Factors limiting the comparison and/or 

285 dissimilarities may also be observed (see Interpretation below for further details).

286 4.4.2 Interpretation

287 Support for inclusion based on class characteristics is an examiner’s opinion that the 

288 observed characteristics provide more support for the proposition that the questioned 

289 impression was made by the known footwear or tire than for the proposition that the 

290 questioned impression was made by a different footwear or tire. However, the relative 

291 support does not rise to the level required for a stronger support for inclusion (based upon 

292 characteristics of use) for the known footwear or tire.

293 Any other footwear/tire that shares the same class characteristics (design and potentially 

294 size) and general wear (if observed) as the known footwear/tire is also included in the pool 

295 of potential sources for the questioned impression.

296 Limiting factors may be present, such as: limited detail, insufficient RACs, improper 

297 photographic techniques, distortion or significant lengths of time between the date of the 
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298 occurrence and when the footwear or tires were recovered that could account for dissimilar

299 characteristics of use. 

300 Any observed dissimilarities shall be interpreted as explainable by the examiner (i.e., no 

301 exclusionary differences are observed).

302 4.4.3 Articulation

303 The questioned impression and known footwear or tire correspond in class characteristics 

304 (design and size, if available). Correspondence of general wear may also be observed. The 

305 observed characteristics of the items provide more support for the proposition that the 

306 questioned impression was made by the known footwear or tire than for the proposition that 

307 the questioned impression came from a different source. 

308 Other footwear or tires with the class characteristics observed in the impression are 

309 included as possible sources. If general wear is observed in the questioned impression, any 

310 differences in general wear with the known shall be explainable by case circumstances (e.g., 

311 time delay between deposition and collection).

312 The examiner shall explicitly detail observations and interpretations regarding:

313 ● The class characteristics observed in the questioned impression and the known 

314 footwear or tire

315 ● Any observed similarities between these characteristics and why these were 

316 interpreted to be correspondences

317 ● Any observed dissimilarities between these characteristics and why these were 

318 interpreted to be explainable

319 ● Any limiting factors that were encountered during the examination and how these 

320 limitations were accounted for, evaluated, and/or mitigated

321 4.5 Support for Inclusion based on Class Characteristics and Specific 

322 Characteristics of Use

323 4.5.1 Observation

324 The questioned impression and known footwear or tire correspond in all observed class 

325 characteristics. Correspondence of general wear (a characteristic of use) may also be 

326 observed. There is also specific wear and/or one or more randomly acquired 

327 characteristic(s) in correspondence. Factors limiting the comparison and/or dissimilarities 

328 may also be observed (see Interpretation below for further details). 

329 4.5.2 Interpretation

330 Support for inclusion based upon class characteristics and specific characteristics of use

331 is an examiner’s opinion that the observed characteristics provide substantially more 

332 support for the proposition that the questioned impression was made by the known 

333 footwear or tire than for the proposition that the questioned impression was made by a 

334 different footwear/tire. However, the relative support does not rise to the level required for

335 strong support for known source.
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336 Any other footwear/tire that shares the same class characteristics and characteristics of use 

337 as the known footwear/tire is also included in the pool of potential sources for the 

338 questioned impression.

339 Limiting factors may be present, such as: limited detail, insufficient RACs, improper 

340 photographic techniques, distortion or significant lengths of time between the date of the 

341 occurrence and when the footwear or tires were recovered that could account for dissimilar 

342 characteristics of use. 

343 Any observed dissimilarities shall be interpreted as explainable by the examiner (i.e., no 

344 exclusionary differences are observed).

345 4.5.3 Articulation

346 The questioned impression and the known footwear or tire share agreement of all class 

347 characteristics and one or more specific characteristics of use. These corresponding 

348 characteristics offer substantially more support for the proposition that the questioned 

349 impression came from the known footwear or tire than for the proposition that the 

350 questioned impression came from a different source.

351 Other footwear or tires with the same class characteristics observed in the impression are 

352 included in the pool of possible sources only if they display the same specific characteristics 

353 of use observed in the questioned impression.

354 The examiner shall explicitly detail observations and interpretations regarding:

355 ● The class characteristics and specific characteristics of use observed in the 

356 questioned impression and the known footwear or tire

357 ● Any observed similarities between these characteristics and why these were 

358 interpreted to be correspondences

359 ● Explanation of why the observed similarities and correspondences were not 

360 sufficient to report strong support for known source

361 ● Any observed dissimilarities between these characteristics and why these were 

362 interpreted to be explainable 

363 ● Any limiting factors that were encountered during the examination and how these 

364 limitations were accounted for, evaluated, and/or mitigated

365 4.6 Strong Support for Known Source

366 4.6.1 Observation

367 The questioned impression and the known footwear or tire correspond in all observed class 

368 characteristics and specific characteristics of use, including one or more randomly acquired 

369 characteristics of high quality and/or discriminability. Dissimilarities may also be observed.

370 4.6.2 Interpretation

371 Strong Support for Known Source is an examiner’s opinion that the observed 

372 characteristics provide overwhelmingly more support for the proposition that the 

373 questioned impression was made by the known footwear or tire than for the proposition that 

374 the questioned impression was made by a different footwear/tire. There is extremely weak 
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375 support for the proposition that the questioned impression was made by a different 

376 footwear/tire.

377 This opinion shall not be expressed using absolutes such as “to the exclusion of all other 

378 sources in the world” or “100% certainty.” Other footwear or tires with the same class 

379 characteristics and specific characteristics of use observed in the questioned impression are 

380 included in the pool of possible sources— which is exceedingly small in the opinion of the 

381 examiner given the quantity, quality, and discriminability of the observed corresponding 

382 characteristics.

383 Any observed dissimilarities shall be interpreted as explainable by the examiner (i.e., no 

384 exclusionary differences are observed).

385 4.6.3 Articulation

386 The questioned impression and the known footwear or tire share agreement of class 

387 characteristics and specific characteristics of use, including one or more RACs of high quality 

388 and/or discriminability. The observed characteristics provide overwhelmingly more

389 support for the proposition that the questioned impression came from the known footwear 

390 or tire than for the proposition that the questioned impression came from a different source.

391 The examiner shall explicitly detail observations and interpretations regarding:

392 ● The specific class characteristics and characteristics of use observed in the 

393 questioned impression and the known footwear or tire

394 ● Any observed similarities between these characteristics and why these were 

395 interpreted to be correspondences

396 ● Explanation of why the observed similarities and correspondences were sufficiently 

397 strong to report strong support for known source

398 ● Any observed dissimilarities between these characteristics and why these were 

399 interpreted to be explainable 

400 ● Any limiting factors that were encountered during the examination and how these 

401 limitations were accounted for, evaluated, and/or mitigated

402 5 General Considerations

403 Proper documentation of the source opinions detailed herein provides transparency, and 

404 aids in the interpretation of the results. Documentation of an examiner’s observations and 

405 findings should be balanced, logical, robust, thorough, and transparent and shall explicitly 

406 describe the bases for conclusions, acknowledging limitations of the information available to 

407 the examiner, and disclosing contextual information or assumptions (if any) used to make 

408 conclusions. All source opinions require such documentation.

409 The source opinions detailed in this document do not refer to the chances that evidence 

410 items originate from a known source or from a different source. This is beyond the scope of 

411 the examiner's responsibilities. Instead, all opinions refer to whether evidence supports the 

412 known source or different source propositions.
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413 6 Limitations

414 When articulating footwear/tire interpretations in reports and testimony, the examiner 

415 shall adhere to the following limitations:

416 ● A source opinion provided in a report or during testimony is ultimately an 

417 examiner’s opinion and is not based upon a comparison to all other footwear/tire 

418 items. 

419 ● An examiner shall not assert that a “strong support for known source” is based on 

420 the “uniqueness” of an item of evidence.

421 ● An examiner shall not use the terms “individualize”, “individualization”, 

422 “identification”, or “match” when describing a source opinion.

423 ● An examiner shall not assert that the known footwear item or tire made the 

424 questioned impression with absolute or 100% certainty, or use the expressions 

425 “reasonable degree of scientific certainty,” “reasonable scientific certainty,” or 

426 similar assertions of reasonable certainty in either reports or testimony.

427 ● An examiner shall not assert that the known footwear or tire made the questioned 

428 impression to the exclusion of all other footwear or tires.

429 ● An examiner shall not provide an “inclusion” opinion without explaining that there 

430 may be other footwear or tires with similar characteristics that could have also 

431 made the impression(s).

432 ● An examiner shall not assert that forensic footwear or tire examinations are 

433 infallible or have a zero-error rate.

434 ● An examiner shall not provide an opinion that includes a numerical estimate of 

435 probability or a statistically-derived measurement except when based on 

436 appropriate data.

437 ● An examiner shall not cite the number of forensic footwear or tire examinations 

438 performed in their career as a direct measure for the accuracy of a conclusion 

439 provided.
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440 Annex A Bibliography

441 Bodziak, W.J. Footwear Impression Evidence: Detection, Recovery, and Examination. 2nd Ed. 

442 Boca Raton, FL: CRC Press, 2000. (https://doi.org/10.1201/9780203755587)

443 Bodziak, W.J. Forensic Footwear Evidence. Boca Raton, FL: CRC Press, 2017. 

444 (https://doi.org/10.1201/b19479)

445 Bodziak, W.J. Tire Tread and Tire Track Evidence: Recovery and Forensic Examination. Boca 

446 Raton, FL: CRC Press, 2008. (https://doi.org/10.1201/9781420006827)

447 European Network of Forensic Science Institutes (ENFSI). ENFSI Guideline for Evaluative 

448 Reporting in Forensic Science (Approved version 3.0), 2016. (https://enfsi.eu/wp449 content/uploads/2016/09/m1_guideline.pdf)

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