Dr D. Barltrop asked:
(a) How were the average water quality data obtained? Were supplies which crossed county boundaries taken into account and were the values obtained volume-weighted?
(b) Do the mortality statistics include data for still-births or early foetal death?
(c) Would the ethnic structure of the populations stated be relevant in this work, and has it been possible to obtain this information?
Professor Kagey, in reply, said:
(a) The water quality data were obtained by averaging municipal water supply data. There are approximately 6 such systems per county which routinely measure the parameters mentioned. In earlier discussions prior to our decision to proceed with this particular set of data, we realized this potential problem. However, we decided to utilize these data as a first look at the state. If our results merit more in-depth analyses we will follow through.
(b) We are not looking at stillbirths or early foetal deaths at this time. These causes of death, as diagnosed in the U.S., are questionable owing to the probability of under-diagnosis. Since we are looking for a rather small effect to begin with, we are concentrating on the major cardiovascular diseases as well as digestive cancers. We do have data on congenital abnormalities which cover a broad spectrum of central nervous system malformations.
(c) Missouri is a fairly homogeneous state and we are studying only the white population, which constitutes over 90% of the state total.
DrM. F. Cuthbert said that the authors had shown a relationship between