Final answer:
Economists deal with the problem of many factors changing at the same time in a market by conducting a marketing audit to systematically assess all the factors influencing the market.
Step-by-step explanation:
When analyzing a market, economists deal with the problem of many factors changing at the same time by conducting a marketing audit. A marketing audit involves gathering information from customers and other stakeholders, finding expert information, and doing a root cause analysis to identify the real problem. By performing a marketing audit, economists can systematically assess all the factors influencing the market and understand their individual impact.