or the "Dutch disease" can make this appear an attractive option by lowering the cost of interest payments on the foreign debt, and they may be considered more creditworthy due to the existence of natural resources. If the resource prices fall, however, the governments' capacity to meet debt repayments will be reduced. For example, many oil-rich countries like Nigeria and Venezuela saw rapid expansions of their debt burdens during the 1970s oil boom; however, when oil prices fell in the 1980s, bankers stopped lending to them and many of them fell into arrears, triggering penalty interest charges that made their debts grow even more. As Venezuelan oil minister and OPEC co-founder Juan Pablo Pérez Alfonzo presciently warned in 1976: "Ten years from now, twenty years from now, you will see, oil will bring us ruin... It is the devil's excrement." A 2011 study in The Review of Economics and Statistics found that commodities have historically always shown greater price volatility than manufactured goods and that globalization has reduced this volatility. Commodities are a key reason why poor countries are more volatile than rich countries. Enclave effects “Oil production generally takes place in an economic enclave, meaning it has few direct effects on the rest of the economy.” Michael Ross describes how there are limited economic linkages with other industries in the economy. Consequently, economic diversification may be delayed or neglected by the authorities in the light of the high profits that can be obtained from limited natural resources. The attempts at diversification that do occur are often white elephant [public works] projects which may be misguided or mismanaged. However, even when the authorities attempt diversification in the economy, this is made difficult because resource extraction is vastly more lucrative and out-competes other industries for the best human capital and capital investment. Successful natural-resource-exporting countries often become increasingly dependent on extractive industries over time, further increasing the levels of investment in this industry as it is necessary to maintain their states' finances. There is a lack of investment in other sectors of the economy which is further exacerbated by declines the commodity's price. While resource sectors tend to produce large financial revenues, they often add few jobs to the economy, and tend to operate as enclaves with few forward and backward connections to the rest of the economy. Human capital Another possible effect of the resource curse is the crowding out