"Runners are far ahead in aging healthfully" NY Times 12 Oct 1994

Running and the development of disability with age, "Annals of Internal 
Medicine" Vol.121, No.7, pp.502-509

1.
a. 451 members of a runners club and 330 nonrunners living in the same 
community.  All were over 50 at the start of the study.
b. 8 years
c. To investigate the long range benefits of vigorous daily exercise on 
physical disabilities.
d. Disability measures included the participants ability to walk, arise 
from a straight chair and grip objects.  Also mobility was considered.
e. The community group - may include people who used to run but have been 
injured.  They may differ according to sex, age, weight, history of 
arthritis, and smoking.

2. I would change how the runners were selected (a).  Others would stay 
the same.

3. In 1989, the questionnaire was modified to increase the sensitivity to 
detect disability.  Figure 1 shows that for the community controls a big 
jump occurred.  Before and after the modification, these 2 groups were 
roughly parallel.

4.  Disadvantages with respect to experiment, we can never be sure that 
the difference is due to a factor which we haven't controlled for.
Disadvantage with respect to cross-sectional is attrition over 
the 8 years.

5. An ever runner is anyone who has ever run regularly for more than one
month.  The study compared ever runners to never runners to include
runners who had quit with those still running, to control for those who
are inclined to run and for those injured runners. 

6.  

7.