Final answer:
Comparative analysis is the most useful research technique for multi-national or single-country market research, as it allows for the comparison of data from different sources or time periods to identify similarities and differences.
Step-by-step explanation:
The most useful research technique for multi-national or single-country market research would be comparative analysis.
Comparative analysis involves comparing data from different sources or different time periods to identify similarities and differences. It allows researchers to understand the variations in market trends, consumer behavior, and competitive strategies across different countries or regions.
For example, a company that wants to expand its business to another country can use comparative analysis to analyze the market conditions, customer preferences, and competitor strategies in that particular country, and compare them with their existing market.