Citation

Haghani M. Int. J. Disaster Risk Reduct. 2023; 93: e103750.

Copyright

(Copyright © 2023, Elsevier Publishing)

DOI

10.1016/j.ijdrr.2023.103750

PMID

unavailable

Abstract

As experimental methods become increasingly popular in crowd dynamics, the question of experimental validity becomes more critical than ever. In fact, there will be no question more fundamental than what makes a crowd experiment valid. For the purposes of design, evaluation and interpretation of crowd experiments, it is paramount that we distinguish between different dimensions of their validity. Here, I differentiate between four categories of experimentation in crowd dynamics based on their underlying purpose of investigation. This includes experiments whose main aim is (i) testing a behavioural theory/hypothesis, (ii) exploring empirical behavioural regularities; (iii) assessing collective (system-level) performance rather than individual behaviour (iv) calibrating and/or validating pre-existing models (including partial/local or full/global model calibration). While delineating various dimensions of external and internal validity as they relate to crowd experiments and enumerating factors that could compromise their validity, I argue how the importance of different validity dimensions varies depending on the investigation's purpose (i.e., the category of experiment). This could provide clarity about circumstances where artificiality/simplicity of laboratory settings is justified as opposed to experiments for which higher levels of contextual fidelity/realism and ecological validity should be given a higher priority. It is critical that investigators (a) be conscious of the trade-off between controllability and realism in their experiment design and (b) identify potential factors that can jeopardise validity of their experiments and take measures to mitigate such threats. Furthermore, it is argued that inferences made from field data do not inherently supersede those of experiments on the issue of validity. Depending on the purpose of investigation, maintaining internal validity sometimes necessitates laboratory settings and justifies artificiality. Naturality of observations per se does not guarantee validity. In the absence of adequate control over the causal relationship, the question of external validity will be futile, as there will be no internally valid inference to be generalised in the first place. Therefore, striking a reasonable balance between internal and external validity of crowd experiments should be made a major design consideration. Overall, the matter of validity is more complicated than the mere creation of a realistic context in the experiment. Studies should not be dismissed merely on the account of ecological validity (contextual realism). The purpose of the design (category of experiment) should be taken into account in making that determination, although the compromise of contextual realism should always be kept to a minimum, and unnecessary compromise should be avoided.

Language: en

Keywords

Evacuation dynamics; Experimental methods; External validity; Internal validity; Pedestrian dynamics