Before World War II the world population was about 2.3 billion and the world Jewish population was about 17 million. Today the world population is about 6.7 billion and the world Jewish population is about 13 million.
Population 1939 - Present
In World War II the world lost 50 to 70 million people, mostly Europeans, including 6 million Jews, which was 35.3% of the world Jewish population. Since 1940, the world human population has grown by about 300% to 6.7 billion, mostly outside of Europe. The Jewish population, however, at about 13 million, while it has grown by roughly 18% since 1945, is roughly 24% lower than it was in 1939. If the world’s Jewish population grew at the same rate as the general population, we would expect a population of 51 million people, not 13 million.
Human population: http://www.census.gov/ipc/www/worldhis.html.
Jewish population: http://www.simpletoremember.com/vitals/world-jewish-population.htm.
Please note that this drawing is not to scale. The time slice between 1939 and 1945 represents 6 years; that between 1945 and 2009 is 64 years. The Jewish population is in the millions, the world population is in the billions, or thousands of millions. The growth in world population is exponential, not linear. However, the picture seems to be a useful representation.