His first York study of 1899 (this was followed up in 1935 and 1951) was a comprehensive survey into the living conditions of the poor in York during which investigators visited every working-class home. This amounted to the detailed study of 11,560 families or 46,754 individuals. The results of this study were published in 1901 in his book Poverty, A Study of Town Life and claimed that 27.84 percent of the total population of York lived below the poverty line. Rowntree defined the poverty line in terms of a minimum weekly sum of money "necessary to enable families... to secure the necessaries of a healthy life", including fuel and light, rent, food, clothing, and household and personal items. This was quantified using scientific methods that hadn't been applied to the study of poverty before. For example, he consulted leading nutritionists of the period to discover the minimum calorific intake and nutritional balance necessary before people got ill or lost weight. He then surveyed the prices of food in York to discover what the cheapest prices in the area for the food needed for this minimum diet were and used this information to set his poverty line. In analysing the results of the investigation he found that people at certain stages of life, for example in old age and early childhood, were more likely to be in abject poverty, living below the poverty line, than at other stages of life. From this he formulated the idea of the poverty cycle in which some people moved in and out of absolute poverty during their lives. Rowntree's argument that poverty was the result of low wages went against the traditionally held view that the poor were responsible for their own plight. The differing approaches to social work often led to heated debates. In the early 20th century, Mary Richmond of the Charity Organization Society (COS) and Jane Addams of the Settlement House Movement engaged in a public dispute over the optimal approach; whether the problem should be tackled with COS' traditional, scientific method that focused on efficiency and prevention, or whether the Settlement House Movement's immersion into the problem, blurring the lines of practitioner and client, was superior. Even as schools of social work opened and formalized processes for social work began to be developed, the question "is social work a profession?" lingered. In 1915, at the American National Conference of Charities and Corrections, Dr. Abraham Flexner spoke on the topic "Is Social Work a Profession?" He contended that it was not because it lacked specialized knowledge and specific application of theoretical and intellectual knowledge to solve human and social problems.