Gudjonsson developed two scales to measure interrogative suggestibility: Gudjonsson Suggestibility Scales I and 2 (GSS I and GSS 2; Gudjonsson, 1984a; 1987c). The aims of the present thesis were to examine issues related to the reliability and validity of these scales. Three studies are presented. Study I assessed the effects of two interviewer styles on measures obtained on the GSS 1. The hypothesis was that a generally abrupt demeanour adopted by the interviewer would lead to higher scores than a friendly demeanour. Results showed that participants tested in the Abrupt condition gained higher scores on two of the post-feedback GSS measures than those tested in the Friendly condition. It was concluded that post-feedback scores may be more sensitive to social aspects of suggestibility than responses to leading questions. Study 2 assessed the effect of the same interviewer demeanours on a sample of adolescents, a more vulnerable population (e. g. Richardson, Gudjonsson, & Kelly, 1995). It was hypothesised that the abrupt demeanour would produce higher GSS I scores, than a friendly demeanour and that this difference would be more marked than that found for normal adults. Results did not support the hypothesis. Scores were lower in the Abrupt condition; this difference was significant for post-feedback responses to leading questions. It was concluded that results provided further evidence that GSS scores are not readily predictable. Study 3 aimed to investigate indicators of "faking bad" on the GSS. It was hypothesised that participants instructed to fake suggestibility would demonstrate a unique scoring pattern. Results supported the hypothesis. It was concluded that an elevated pre-feedback score in the absence of any other raised scores may indicate malingering on the GSS. Issues related to the reliability and validity of the scales are discussed.

The present thesis deals with the psychological aspects of interrogative suggestibility of witnesses, victims and offenders involved in criminal investigation. The first part of the work offers a theoretical and literary overview of important theoretical findings on suggestibility in the field of psychology which underly the teoretici model of interrogative suggestibility by Gudjonsson and Clark. Their model is introduced in relation to selected psychological characteristics with an emphasis on practical overlap in forensic psychology and criminal practice. The theoretical part is concluded with a detailed introduction into the Gudjonsson scales of suggestibility - GSS 1 and GSS 2. In the empirical part of the thesis, the author focuses on adaptation and validation of GSS 1 in the Czech environment. The outcome of this work are the psychometric characteristics of the Czech version of the GSS 1, including detailed instruction for administration and evaluation and statistical norms for the czech population. Currently Czech criminalist dispose of no suitable psychodiagnostic assessment method to evaluate the interrogative suggestibility. Key words: interrogative suggestibility, GSS 1, Gudjonsson, psychodiagnostics