They are similar but not the same. Most requires their members to abide by their standards and code of ethics by placing the inspector on a honor system. Most inspectors don't belong to any type of home inspectors' organization, and are not obligated to abide by any inspection standards or code of ethics. The chosen inspector or inspection company decides the amount of time and inspection format. But having those designations do not guarantee a better home inspection.
Some organizations only certify or register their own members.
Some only requires a fee paid, others requires taking a test, proving experience by the amount of completed paid inspections, completing yearly continuing education credits requirements and paying a fee. Inspectors are not evaluated nor monitored on adherence to the organization's minimum standards of practice or code of ethics, to receive and maintain a lifetime certification or registration. Inspectors are evaluated and investigated for compliance of these standards and code of ethics set by the Institute. Certifications or registrations do not guarantee the home inspector will be thorough, or has the vast construction knowledge and experience needed to perform a thorough home inspection. Only the Institute scrutinizes all home inspector appliants for certification.