External benchmarking using trend analysis involves comparing a company's performance metrics with industry standards or averages over a certain period to identify trends and areas for improvement. Comparing common-size financial statements of the subsidiary with the averages of the industry for the last two periods allows for a normalized comparison by expressing financial statement items as a percentage of a common base figure (e.g., total assets or sales). This method highlights the subsidiary's financial structure and performance trends in relation to industry norms, facilitating a comprehensive analysis. References:

"Internal Auditing: Assurance & Advisory Services" (The Institute of Internal Auditors)

"Benchmarking: An Essential Tool for Assessment, Improvement, and Market Leadership" (Michael J. Spendolini)