7Ihe Longitudinal Study of Social, Economic and Demographic Change in Thailand, a national sample survey covering a broad range of topics, is being conducted by the Institute of Population Studies of Chulalongkorn University. It is the first and only survey o'f its kind in Thailand and has systematically collected a vast array of information on the characteristics and behavior of the Thai population not available from any other source on a national level. The Longitudinal Study began in 1968 with an initial stage of planning and preparations. The first rounds of interviews took place in rural areas in April and May 1969 and in urban areas (defined as officially designated municipal areas) one year later. Both rural and urban samples were essentially national in scope, although for various reasons certain areas (most notably the four predominantly Muslim provinces in the south of Thailand) were excluded from the sampling universe. For the rural survey the population of the excluded areas constituted about 18% of Thailand's total rural population; for the urban survey the excluded areas comprised about 5% of the total urban population. The 1969 rural sample contained about 1500 households and the 1970 urban sample about 2000 households. Taken together (and properly weighted), the two :samples constitute an essentially national sample of the Thai population. When considering the results of each sample it is important to bear in mind that the Thai population lives predominantly in rural areas. According to preliminary results of the 1970 census, less than 15% 'of the total population resides in municipal areas. Furthermore, over half of the urban population lives in the capital, BangkokThonburi, which is over 30 times larger than the largest provincial town. For both samples, data was collected through interviewing the household head,