Polygraph seems to be a tool to discriminate against applicants they cannot otherwise flush out of good government jobs. Investigators will lie about the process to get any inconsistent or conflicting information from you. As soon as you do you are toast. They will ask same questions over and over, ask you to elaborate, tell you that you won't be disqualified for providing additional information. If you change any information however slight they will use it to fail you. You can only fail a polygraph by your own admissions.