The China Study by Thomas Campbell

356 THE CHINA STUDY

of comprehensiveness, quality and uniqueness greatly improved the

credibility and reliability of the findings-by far. Indeed, the New York

Times, in a lead story in its Science Section, called the study "The Grand

Prix" of epidemiological studies.

COMPREHENSIVENESS OF DATA
This survey was, and still is, the most comprehensive of its kind ever
undertaken. After all the blood, urine and food samples were collected,
stored and analyzed, and after the final results were tabulated and evalu-
ated for quality (a few suspect results were not included in the final
publication), we were able to study 367 variables. These represented
a wide variety of dietary, lifestyle and disease characteristics, now in-
cluded in a dense 896-page monograph.l There were:

• disease mortality rates on more than forty-eight different kinds of
  disease^2 ;


• 109 nutritional, viral, hormonal and other indicators in blood;


• over twenty-four urinary factors;


• almost thirty-six food constituents (nutrients, pesticides, heavy
  metals);


• more than thirty-six specific nutrient and food intakes measured in
  the household survey;


• sixty diet and lifestyle factors obtained from questionnaires;


• and seventeen geographic and climatic factors.
  The study was comprehensive, not only because of the sheer number
  of variables, but also because most of these variables varied over broad
  ranges, as with the cancer mortality rates. Broad ranges strengthened
  our ability to detect important preViously undiscovered associations of
  variables.

QUALITY OF DATA

A number of features added quality to this study.

• The adults chosen for this survey were limited to those who were
  thirty-five to sixty-four years of age. This is the age range in which
  the diseases being investigated are more common. Information on
  death certificates of people older than sixty-four years was not in-
  cluded in the survey because this information was considered less
  reliable.