Morbidity and mortality during the health transition: a comment on James C. Riley, ‘Why sickness and death rates do not move parallel to one another over time’

Throughout most parts of the world, mortality rates have fallen dramatically since
the mid-nineteenth century, but morbidity rates appear to have risen.1 James
Riley's article is the latest in a series of attempts to explain this paradox. It breaks
new ground, in relation to the author's previous work, in its use of a mathematical
model to explain the relationship between morbidity and mortality, and in the
deployment of new data from the Abthorpe, Ashboume, Llangeitho, and Morcott
Friendly Societies.2 However, despite the undoubted importance of Riley's
article, many of his conclusions remain open to question.
In endeavouring to explain 'why sickness and death rates do not move parallel to
one another over time', Riley raises four major issues, which may be summarized
as follows:
1. What is the practical significance of the equation P = / X D?
2. To what extent has Riley succeeded in demonstrating the robustness of the
friendly society data as objective indicators of health status?
3. What do the data reveal about sickness and health among members of the four
societies?
4. What are the implications of Riley's findings for our understanding of the
relationship between morbidity and mortality during the period of the 'health
transition'?
This comment will attempt to highlight the questions raised by Riley's article
under each of these headings.
What is the practical significance of the equation P= IX D?
To what extent has Riley succeeded in demonstrating the robustness of the
friendly society data as objective indicators of health status?
What do the data reveal about sickness and health among members of the four
Societies?
What are the implications of Riley's findings for our understanding of the
relationship between morbidity and mortality during the period of the 'health
transition'?