<Li> In stage three, birth rates fall due to various fertility factors such as access to contraception, increases in wages, urbanization, a reduction in subsistence agriculture, an increase in the status and education of women, a reduction in the value of children's work, an increase in parental investment in the education of children and other social changes . Population growth begins to level off . The birth rate decline in developed countries started in the late 19th century in northern Europe . While improvements in contraception do play a role in birth rate decline, it should be noted that contraceptives were not generally available nor widely used in the 19th century and as a result likely did not play a significant role in the decline then . It is important to note that birth rate decline is caused also by a transition in values; not just because of the availability of contraceptives . </Li> <Li> During stage four there are both low birth rates and low death rates . Birth rates may drop to well below replacement level as has happened in countries like Germany, Italy, and Japan, leading to a shrinking population, a threat to many industries that rely on population growth . As the large group born during stage two ages, it creates an economic burden on the shrinking working population . Death rates may remain consistently low or increase slightly due to increases in lifestyle diseases due to low exercise levels and high obesity and an aging population in developed countries . By the late 20th century, birth rates and death rates in developed countries leveled off at lower rates . </Li> <Li> Some scholars break out, from stage four, a "stage five" of below - replacement fertility levels . Others hypothesize a different "stage five" involving an increase in fertility . </Li> <P> As with all models, this is an idealized picture of population change in these countries . The model is a generalization that applies to these countries as a group and may not accurately describe all individual cases . The extent to which it applies to less - developed societies today remains to be seen . Many countries such as China, Brazil and Thailand have passed through the Demographic Transition Model (DTM) very quickly due to fast social and economic change . Some countries, particularly African countries, appear to be stalled in the second stage due to stagnant development and the effect of AIDS . </P>

In what stage of the dtm are most countries of the world