impact of oil wealth on democratization. A 2016 study challenges the conventional academic wisdom on the relationship between oil and authoritarianism. A 2022 study found that the resource curse is only tied to easily extractable oil, but not oil that requires complex extraction. Other forms of resource wealth have also been found to strengthen autocratic rule. A 2016 study finds that resource windfalls have no political impact on democracies and deeply entrenched authoritarian regimes, but significantly exacerbate the autocratic nature of moderately authoritarian regimes. A third 2016 study finds that while it is accurate that resource richness has an adverse impact on the prospects of democracy, this relationship has only held since the 1970s. A 2017 study found that the presence of multinational oil companies increases the likelihood of state repression. Another 2017 study found that the presence of oil reduced the likelihood that a democracy would be established after the breakdown of an authoritarian regime. A 2018 study found that the relationship between oil and authoritarianism primarily holds after the end of the Cold War; the study argues that without American or Soviet support, resource-poor authoritarian regimes had to democratize while resource-rich authoritarian regimes were able to resist domestic pressures to democratize. Prior to the 1970s, oil-producing countries did not have democratization levels that differed from other countries. Oil Abundant authoritarian governments are suggested to earn high levels of income for oil but spend an extremely minimal amount on social expenditures for individuals being ruled while democracies are suggested to opposite. Research by Stephen Haber and Victor Menaldo found that increases in natural resource reliance do not induce authoritarianism, but may instead promote democratization. The authors say that their method rectifies the methodological biases of earlier studies which revolve around random effects: "Numerous sources of bias may be driving the results [of earlier studies on the resource curse], the most serious of which is omitted variable bias induced by unobserved country-specific and time-invariant heterogeneity." In other words, this means that countries might have specific, enduring traits that gets left out of the model, which could increase the explanation power of the argument. The authors claim that the chances of this happening is larger when assuming random effects, an assumption that does not allow for what the authors call "unobserved country-specific heterogeneity". These criticisms have themselves been subject to criticism. One study re-examined the Haber-Menaldo analysis, using Haber and Menaldo's