A relatively under-explored topic in the current literature on and methods for research in the field of comparative and international education is the problem of investigator bias in cross-cultural research. This article discusses the nature of and an approach to address investigator bias in research that originates from the theory-ladenness of observation. Theory-ladenness essentially holds that everything one observes or perceives is influenced by and interpreted through one's existing beliefs, values, assumptions and expectations. This article explains how the philosopher Ludwig Wittgenstein's exposition of belief system--what he calls "world-picture"--illuminates our understanding of investigator bias and theory-ladenness by elucidating the organisation, inculcation and revision of beliefs. It is further proposed that comparativists confront the challenge of investigator bias by critically reflecting on their world-picture, the impact of their world-picture on their theoretical commitment and research process, and the evaluation and revision of their theory through the interaction between theory and data.