polygraph Flashcards
what is a polygraph
set of equipment that accurately measures various sorts of bodily functions i.e heart rate, palmar sweating
polygraphs in general: BPS 2004
procedures involved are not standardised to the extent that they may be described as satisfactory in psychometric terms. no easy means of checking on the practices and procedures employed by the polygraphers. Some aspects (misleading the examinee) might be contrary to British law
Relevant/ Irrelevant technique
2 types of questions: crime relevant or irrelevant. Crime relevant questions are related to crime under investigation. Irrelevant question’s are not related to the crime, the examiner knows that the examinee will have to answer these questions truthfully. Examiner compares psychological responses to both types of questions. Rationale behind is that larger responses to relevant questions than irrelevant questions indicate that the examined was lying while responding to the crime relevant questions
RIT: BPS 2004
Premise used in RIT tests are incorrect, a strong response could occur when truthful examinees are afraid of not being believed. Clear that RIT is an inappropriate technique and should not be used
RIT: US research council 2003
RIT is not normally standardised for question selection or interpretation. examiners typically interpret the results globally by inspecting the charts to see whether there is a stronger pattern to relevant questions. Not possible to draw conclusions about accuracy as procedure can vary across examiners
Control Question Test
compares responses to relevant questions with response to control questions. Relevant questions = questions about the crime. Control questions deal with acts that are not directly associated are indirectly related to the crime and do not refer to the crime in question (general in nature, deliberately vague, and cover long periods of time). The examinee has no choice but to lie when answering these questions. Based on the assumption that an innocent suspects control questions will generate more arousal than relevant questions. Innocent examinee will be concerned with control questions as examiner puts so much emphasis on control questions, examinee knows they are lying.
CQT: BPS 2004
Method may be improvement compared to RIT. the alternative explanations for heightened arousal when answering RQ, fear of not being believed can not be ruled out. examiner misleads the examinee can be seen as unethical in some countries as guidelines on testing typically involve informed consent. test is not standardised as CQ depend on crime investigation
CQT: Carroll 91
guilty: 83% correct, 17% incorrect
innocent: 53% correct, 47% incorrect
CQT: Hunts & Perry 1991
guilty: 86% correct, 11% incorrect
innocent: 59% correct, 30% incorrect
Directed lie test
control questions are standardised and can be asked in all situations i.e before the age of 27 have you ever told a single lie? examinees instructed to answer no to these questions and asked to think about particular situations in which they did tell a lie or break a rule during denials. Guilty suspects thought to be mostly concerned with RQ and expected to show strongest responses to these questions.
DLT: BPS 2004
relevant questions might be more arousing than CQ and a fear of not being believed while replying to RQ remain
DLT: US research council 2003
only applicable under restricted conditions: is a specific incident, activity or thing that can be subject of questioning and several details only known to investigators
Guilty knowledge test
examines whether examinee posses knowledge about a particular crime that they do not want to reveal. examiner will show suspect several items (i.e. type of knife) for each examinee they will be asked if they recognise the knife. both innocent and guilty will deny each time that they recognise the item, a guilty examinee with recognise the knife.
GKT: US research council 2003
truthful examinees under certain circumstances show physical patterns similar to those expected from deceptive examinees. Cardiovascular and electrodermal measures measures are all lumped together, different measures are all lumped together - different measures respond differently to psychological states
GKT: Elaad 1990
guilty: 42% correct, 58% incorrect
innocent: 98% correct, 2% incorrect
