The effect of tape type, taping method and tape storage temperature on the retrieval rate of fibres from various surfaces: An example of data generation and analysis to facilitate trace evidence recovery validation and optimisation.

This paper aspires to assist those tasked with data generation and analysis for the purpose of the validation and/or
optimisation of trace evidence recovery. It does so via a detailed report of the authors’ approach to this problem in the
context of target fibre retrieval using self-adhesive tapes. Textile fibres can provide valuable evidence at both source
and activity levels. This ability stems from their near ubiquity in the man-made environment, their potential for high
levels of discrimination (especially when found in combination) and their reproducible transfer and persistence
behaviours. To realise this value for the criminal justice system, it is vital that police forces and forensic providers are
collectively able to search for, recover and analyse fibres found at crime scenes and correctly evaluate their evidential
value. ISO accreditation provides quality assurance for such activities. The work reported in this paper was part of a
study to validate crime scene fibre retrieval processes for the purposes of ISO17020 accreditation. However, it is
hoped that it will be of assistance to those wishing to validate and/or optimise forensic fibre recovery whether at the
crime scene or in the laboratory. Further, the methods described may be of value to those who need to validate and/or
optimise the recovery of other types of trace evidence. This paper outlines a series of experiments that investigated
the effect of four factors on the rate at which target fibres could be recovered from surfaces by tape lifting. The factors
were tape type (with two levels, namely: J-LAR and Crystal Tabs), tape storage temperature (three levels: -5˚C, room
temperature [19±1˚C] and 35˚C ), taping method (two levels: zonal and one-to-one) and surface (12 levels: each being
a surface type commonly encountered at crime scenes). This resulted in 144 unique experimental conditions. For each
of these, five repeat fibre recovery rate determinations were carried out, generating 720 data points. All surfaces were
clean and dry prior to target fibres being transferred and recovered. In all cases, the tapes were applied to the surfaces
at 19±1˚C. These experiments showed that the surfaces can be divided into three stable clusters based on the median
and interquartile range of the fibre retrieval rate achieved from each of them. Also, they showed that, in terms of the
proportion of the target fibres retrieved, typically and setting aside interaction effects: • Crystal Tabs outperformed JLAR;
• rolls of tape stored at -5˚C and 35 ˚C outperformed those stored at room temperature; • one-to-one taping
outperformed zonal taping. However, notably, a good degree of between-condition overlap was also apparent in the
data. To understand this, a four-way factorial ANOVA model was built which revealed significant and substantive
effects for all four main effects and for 10 of the 11 interactions. Importantly, the four-way interaction term was
amongst those found to be significant. The interplay between the effects of the four factors was analysed by means of
simple effects tests and pairwise contrasts. Tables and interactive parallel coordinate plots have been created. Using
these it can easily be seen which of any given pair of levels of each of the four factors resulted in the higher fibre
retrieval rate under any one of the unique conditions of the study, and the effect size and statistical significance of this
observation. Qualitative evaluations of the effect of tape storage temperatures on tape pliability and its propensity to
tear in use were also made.