Simpson Enquiry (1930), the Passfield White Paper (1930), the Peel Commission report (1937), and the Survey of Palestine (1945). However, the Hope Simpson Enquiry did note that there was significant illegal immigration from the surrounding Arab territories, while the Peel Commission and Survey of Palestine claimed that immigration played only a minor role in the growth of the Arab population. The 1931 census of Palestine considered the question of illegal immigration since the previous census in 1922. It estimated that unrecorded immigration during that period may have amounted to 9,000 Jews and 4,000 Arabs. It also gave the proportion of persons living in Palestine in 1931 who were born outside Palestine: Muslims, 2%; Christians, 20%; Jews, 58%. The statistical information for Arab immigration (and expulsions when the clandestine migrants were caught), with a contrast to the figures for Jewish immigration over the same period of 1936–1939, is given by Henry Laurens in the following terms Palestinian immigration 1936-1939 {| class="wikitable" |- ! Jews !! Arabs |- | rowspan=1 | 69,716 ||2,267 |- |} Expulsions of illegals, 1937-1938 {| class="wikitable" |- ! Jews !! Arabs (et al.). |- | rowspan=1 | 125 ||1,704 |- |} According to Mark Tessler, at least some of the Arab population growth was the result of immigration, mostly from the Sinai, Lebanon, Syria, and Transjordan, stimulated by the relatively favorable economic conditions in Palestine, but he noted differing opinions among scholars over how substantial it was. He cited one study as putting the Arab population growth attributable to immigration between 1922 and 1931 at 7%, meaning that 4% of the Arab population in 1931 was foreign-born, while noting another estimate put the growth in the Arab population attributable to immigration at 38.7%, which would mean that 11.8% of the Arab population in 1931 was foreign-born. Tessler wrote that "Israeli as well as Palestinian scholars have disputed this assertion, however, concluding that it is at best a theory and in all probability a myth." In a 1974 study, demographer Roberto Bachi estimated that about 900 Muslims per year were detected as illegal immigrants but not deported. He noted the impossibility of estimating illegal immigration that was undetected, or the fraction of those persons who eventually departed. He did note that there was an unexplained increase in the Muslim population between 1922 and 1931, and he did suggest, though qualifying it as a "mere guess", that this was