Which type of evidence would an IS auditor consider most reliable?

The most reliable type of evidence for an IS auditor is the results from tests performed by external IS auditors. This type of evidence is viewed as more credible because it has been conducted by independent professionals who are not affiliated with the organization being audited. The independence of external auditors helps ensure objectivity in their findings, minimizing potential bias that could arise from internal stakeholders.

External auditors often apply standardized and well-established testing methodologies, leading to higher assurance in the results obtained. Their work is based on an assessment of the organization's systems, processes, and controls, and is subject to professional standards and scrutiny, making it a valuable reference point for auditors.

In contrast, the other types of evidence can have limitations. Peer reviews might reflect subjective assessments from individuals who may have vested interests or influences on the outcome. Documentation provided by the organization, while important, may not be completely unbiased, as it is generated internally and may lack external validation. Internal audit report findings are also crucial but are influenced by the organization and may not carry the same weight as external assessments due to potential conflicts of interest.

Thus, results from tests performed by external IS auditors stand out as the most reliable evidence due to their independence, objectivity, and adherence to professional auditing standards.