Holland (1967) measured LOC of his participants and replicated Milgram's study. He found 37% of internals did not continue to maximum voltage compared to 23% externals.
Twenge et al (2004) criticise the idea of LOC following the review of 40 years of data, showing people became more resistant and more external over time. This contradicts previous research.
Rotter (1982) argues that LOC is not the most important factor in determining resistance, it can depend on the situation.