The number of people counted in the census of 1381 was 59,873,305; however, this number dropped significantly when the government found that some 3 million people were missing from the tax census of 1391. Even though underreporting figures was made a capital crime in 1381, the need for survival pushed many to abandon the tax registration and wander from their region, where Hongwu had attempted to impose rigid immobility on the populace. The government tried to mitigate this by creating their own conservative estimate of 60,545,812 people in 1393. In his "Studies on the Population of China", Ho Ping-ti suggests revising the 1393 census to 65 million people, noting that large areas of North China and frontier areas were not counted in that census. Brook states that the population figures gathered in the official censuses after 1393 ranged between 51 and 62 million, while the population was in fact increasing. Even the Hongzhi Emperor (r. 1487–1505) remarked that the daily increase in subjects coincided with the daily dwindling amount of registered civilians and soldiers. William Atwell states that around 1400 the population of China was perhaps 90 million people, citing Heijdra and Mote.