Definition: Unbiased sample
OECD - Business tendency surveys
A sample drawn by a method which is free from bias. This implies not only freedom from bias in the method of selection, e.g. random sampling, but freedom from any bias of procedure, e.g. wrong definition, non-response, design of questions, interviewer bias, etc.
Organization for Economic Cooperation and Development (OECD), "Business Tendency Surveys - A Handbook", OECD, Paris, 2003