The accuracy of demographic data is critical to an understanding of regional and global environmental issues. The need for accurate and unbiased information is particularly acute in China where population growth could outpace agricultural yields and undermine economic development. While there is a general perception that government statistics are correct and unbiased, a number of social, economic and policy factors can result in significant errors. Jiang described many of the problems associated with the collection of statistical data in China and particularly emphasized the factors that lead to under - and over - reporting of population data from the 1950s to the 1990s. In addition, he described the factors that have influenced the development of official Chinese population policy and the prospects for agricultural development to support the growing population into the future.

To gain a better understanding of the problems associated with census taking in China, one can examine four censuses in China between the 1950s and 1990s (1953, 1964, 1982, 1990). Each of these censuses has been used to correct the under- or over-reporting of population in the regular population registration. To understand the causes and extent of these errors, additional surveys have been conducted by the Chinese government. The results of these surveys allow an examination of the reasons that underlie the biases in the final population data so that the demographic data published in the year books will be reliable.

In 1964, a survey was conducted in which 8 million people were removed from the population registry. Of these 8 million, about 6 million were found to be dead and the remainder were found to be non-existent. The significant over-reporting of population during this period was likely the result of a quota system and the control of agricultural land by production teams. Because of these government policies, agricultural resources were allocated on the basis of family size, creating a tremendous incentive for over-reporting.

In the 1970s and 1980s, government surveys indicated significant under-reporting, particularly in rural regions of China. These errors probably were the result of population control/responsibility programs that levied taxes based on family size. Allocation of agricultural resources no longer favored over-reporting as families were given control over land and the production team system was discontinued. In addition to policy-oriented biases, social traditions contributed to under-reporting. Because females are traditionally associated with their future husband's family, they are sometimes not reported as the children of their biological parents.

The Chinese government uses two primary methods to correct reported population data. The first is a sample survey of roughly 1.8 million people annually. In addition to the primary survey, an additional small survey is undertaken with highly trained personal and is used to correct the larger survey. In some cases, the results of the small survey can in crease birth rate estimates by 2 percentage points. Starting in 1990, censuses are conducted every 10 years with smaller sample censuses in the intercensus years. These data from the smaller sample censuses can also be used to correct economic data. For example, in industrial towns there is often an over-reporting of economic outputs. In one instance, a townships' output was scaled down by 30% following corrections. The reasons for these errors vary from region to region and are not always overestimates. In rich areas there tends to be an under-reporting of income because only direct forms of income are taken into account. The reasons for under-reporting are probably related to a desire to not appear overly wealthy and thus subject to greater taxation. In poor areas, the opposite is true, and the tendency is to report all economic activity that roughly qualifies as income. This may be due to the desire of local officials to appear economically successful. In addition, there is a pressure to demonstrate year-to-year increases in economic activity as decreases would be viewed as a failure.

In the last several decades, the Chinese population problem has become a major focus of government policy. In the 1950s, Chinese population had already reached 600 million (about 25% of the world population at the time). But at that time, there was not much serious government attention. Although the 1956 five-year agricultural production plan contained population targets, these targets were not taken seriously or rigorously encouraged. The rapid population increases in the 1960s began to result in serious government attention. In calculations based on the 1960s growth rates, doubling time amounted to 30 years. By 2000 then, China would have had a population of 1.6 to 1.7 billion people and this would have reached 6 billion by the mid 2000s. As a result, the population problem became a focus for the national government. By 1962, a family planning program was introduced to major cities and some of the coastal areas. But after 1966, the process was interrupted by the cultural revolution. The programs were started again in 1972 and were expanded to the whole country. By the end of the 1970s, Chinese population approached one billion and the government tightened its program, making it one of the most rigorous in the world. One common misperception of this period however, is that the policy is strictly one child per family. In reality, the population program should be viewed as a 1 to 2 children per family policy, with some families reaching 3 to 4 children.

As China moves into the future there are several major problems that will need to be addressed. Chief among these is energy consumption. Per capita energy consumption in China averages less than 0.4 tons of standard coal. Compared to an average of 1.7 in developed countries and 8 to 9 in the United States, the Chinese average has no direction to go but up.

Another serious problem is soil erosion which is estimated to affect 38% of the total land area of China. Desert expansion due to the degradation of grassland is also a major problem as one third of the total grassland area is degraded. As a result, fewer cows can be grazed on a given area of land and grazing efficiency is lowered. Water use is also a critical issue as current Chinese water availability is roughly 1/4 of the global average and groundwater stores are already threatened.

Use of grain in China will also be an important issue as China continues to increase the amount of grain imported from abroad. Grain production in some areas of China has been somewhat decreased due to conversion to cash crops and conversion of land from agricultural to industrial uses. It is also important to note that current grain imports are directed to urban areas and in many rural farming areas, individual families have grain stores. Development of cities will then be a critical component in future Chinese agricultural policy.

At the moment, the Chinese government is hoping to increase grain production by increasing areas used for grain production, increasing the use of two cropping systems, and increasing the contribution of technology to grain production by increasing nitrogen and phosphorous fertilizer use and through soil surveys and land analysis. Efforts are also being made to create new high-yield varieties of grain and improved irrigation systems.