Expert method used for data collection
Expert method or methods according to [86] use the knowledge and practical experience of experts in the relevant field to obtain: estimates of non-measurable quantities, estimates of data that are not available and the acquisition of which would be disproportionately difficult, estimates of future development (state), proposal of creative solutions, etc. Typically the use of experts in the mentioned set of methods are narrow specialized problems, or especially general, complex and complex problems (i.e. complex and poorly structured, weakly formalized, unique and unrepeatable, with a lack or complete absence of objective qualitative information, etc.) [86]. The expert investigation took place in the following stages:
- A selection of experts.
- Obtaining expert testimony.
- Evaluation of expert testimony.
The quality of the selection of experts directly affects the quality of the obtained analysis results. Decisive influences are the number of experts (i.e. for the statistical significance of the obtained results) and their relevant characteristics (e.g. competence, creativity, relation to the topic, conformity, analytical thinking and breadth of thinking, constructiveness, self-criticism, tolerance) [86]. Determining the number of experts and choosing suitable properties are parameters dependent on the choice of method for obtaining expert statements and at the same time they affect the costs of the analysis, i.e. financial and time.
Obtaining expert statements can take place in several ways, according to [86] according to: the way organizers communicate with experts, the level of communication between experts during the expert investigation, the frequency of obtaining information, the degree of standardization.
For the purposes of the dissertation, a multi-stage Delphi method was chosen.
4.1.1 The multi-stage Delphi method
The mentioned multi-stage Delphi method [23,86] is a method of obtaining expert statements with the following properties [86]:
- multi-round survey with feedback,
- there is a systematic clarification of the opinion of the group of experts,
- anonymity of experts,
- information feedback,
- experts have both group opinion and atypical opinions available before the next round,
- the possibility to take into account circumstances that the expert was previously unaware of,
- or the possibility of reconsidering an atypical opinion,
- if the expert insists on an atypical opinion, he must justify it.
Obtaining statements takes place in several rounds, in which the latest results are gradually refined. The termination of the method occurs when the “consensus” of the experts is reached, or when the stability of the individual statements is achieved [86]. The disadvantage of the Delphi method is that it is time-consuming and more laborious to process questions aimed at the desired results, process survey questionnaires and interpret the results for their completion in the next round, respectively. response rate.
According to [86], the evaluation of expert statements takes place in two phases: determining the group opinion, and assessing the quality of the information obtained. Determining group opinion can be done using quantitative (arithmetic mean, mode or median, distribution, statistical characteristics – variance, quantile range, interval estimates, distribution characteristics) or qualitative estimates (nominal scale, conversion to point quantitative scale, formalization and quantification of responses).
4.1.2 The use of the Delphi method for the safety research of subway operation
The aim of the research carried out in cooperation with the employees of the Transport Company hl. of Prague was the verification of methods for evaluating critical infrastructure and determining the criticality of system elements. The research was carried out in the form of an expert investigation. Each expert was interviewed using an electronic form [5,16], and was asked to fill it out by e-mail.
The group of experts was chosen on the basis of references from selected employees of the metro operator and from selected service providers and suppliers of key equipment required for the operation of the metro. Each expert approached in this way had the opportunity to recommend other suitable experts in the following areas: occupational safety and personnel health protection, property protection, traffic economy, passenger protection, technical and functional traffic safety.
The condition for recommending an expert to the expert team was his long-term knowledge of metro operations with experience in the various areas mentioned above and at various levels of management, i.e.: strategic management, tactical and project management, operational management, technical worker, technical work.
A total of 18 experts were approached, who were asked to fill out a short questionnaire to determine the expert’s qualifications according to [86], before starting the investigation.
Questioning using the Delphi method was divided into a total of 3 phases:
- Identification of assets (functions, locations and parts of the metro system that are important for its safe operation).
- Determining importance and vulnerability.
- Impact scenarios of selected disasters.
At the end of each round of questioning, the results were evaluated, and in case of disagreements, clarification and justification was carried out, which also took place in several iterations. The survey process and individual questions for each round are listed in Appendix A.
4.1.3 Used Scales
In the mentioned security research and in the submitted dissertation, we work with criticality K as a function of importance D and vulnerability Z, in accordance with the definition in paragraph 2.1.3:
K = D x Z
(21)
The mentioned quantities depend on the level of the security management system at which we assess the given quantity, i.e. according to the Defense-In-Depth approach (paragraph 2.1.7 and 2.3.4) and according to the source [18] we monitor the following levels (a more detailed description of the levels for the purpose of the subject research is in Appendix A):
- Safe metro operation under normal conditions (control level L1).
- Safe subway operation under abnormal conditions (control level L2).
- Safe operation of the metro in case of major deviations / accident management (management level L3).
- Management of metro operations and assets in case of critical conditions (management level L4).
- Management of metro operations and assets in case of extreme conditions (management level L5).
For quantities D and Z, ordinal scales were used, i.e. scales ranging from 1 to 3, with consideration of criteria for critical infrastructure [34,35]. A description of each numerical value is given in paragraph A.2.1 of Annex A.
Division of disasters into relevant, specific and critical categories according to the All-Hazard-Approach (paragraph 2.1.2 and 2.1.7).