Twenge conducted a meta-analysis of American LOC studies that took place over 40 years. They found that over time, people became more resistant to social influence, but the number of people with an external locus of control also increased. This suggests that Holland's research is invalid as based on their findings, people with an internal locus of control are more likely to resist social influence, not those with an external LOC. This questions the validity of the LOC as an explanation for resistance to social influence.