These high enrollment rates are a recent phenomenon. High income countries had on average a tertiary gross enrollment ratio of only 24% in 1970. This ratio has reached over 75% in just under 50 years. Upper middle income countries have seen an even bigger growth, going from 10% (1993) to over 53% (2018) in only 15 years. Lower middle income and low-income countries have also seen considerable tertiary enrollment growth since the mid-1990s, growing 300% and 100% in 15 years.