An auditor wants to determine the rate at which transactions may have been recorded incorrectly by the accountants of the firm he is auditing. However, the client firm has processed thousands of transactions of different dollar amounts in the past year, and it is infeasible to examine all of them. He decides to select randomly ten transactions whose amount was under $100,000, another ten transactions whose amount was between $100,000 and $200,000, and continue with selecting ten transactions from each successively higher category until he has assembled 100 loans to analyze. What is the POPULATION that the auditor is investigating? What kind of selection process did the auditor use?