Cognition and Neuropsychology 489age, there is an increasing recognition of new diseases,
and discovery of treatments and cures for old diseases. The
de“nition is fundamental to the study of interactions between
aging and disease.
Despite the attention this issue has received, there is still no
de“nitive answer to what is disease, what is primary aging,
and which, if any, diseases are irreversible. The fact that the
diseases, once thought to be intrinsic to the aging processes,
are being identi“ed every day serves to place us on shifting
sand. Today•s primary aging variable is tomorrow•s secondary
aging variable. J. G. Evans of Oxford University states this
most eloquently: •In fact to draw a distinction between disease
and normal aging is to attempt to separate the unde“ned from
the inde“nableŽ (Evans, 1988, p. 40). Despite the dif“culty in
making distinctions between primary and secondary aging
caused by progress in diagnostics and treatment, it is neces-
sary to make this distinction for each patient and to do so ex-
plicitly. The •age variableŽin any experiment or analysis is an
empty variable unless operationally de“ned or indexed.
Not only are there research implications with respect to our
conceptions of primary and secondary aging, but there are also
signi“cant implications for treatment. Evans (1988) summa-
rizes these issues and argues that the distinction between
normal aging and disease has arisen from clinical medicine be-
cause of its tradition of thinking dichotomously, that is, if one
must treat or not treat, it then becomes important to think in
terms of disease or nondisease. Most importantly, he argues that
the disease and nondisease model is inappropriate for clinical
practice with the elderly because it precludes nontraditional in-
terventions and allows physicians to dismiss potential medical
problems as the natural consequence of aging. Siegler and
Costa (1985) point out that patients may seek treatment if they
do not dismiss changes in health and behavior as an inevitable
consequence of aging. In a classic study, Dye and Sassenrath
(1979) reported that health care professionals classi“ed as
•normal agingŽany condition associated with the onset of old
age, even though that condition could be treated or reversed.
INTERACTIONS WITH OTHER DISCIPLINES
Both aging and disease are dynamic processes, and the study
of these processes is inherently multidisciplinary involving
particularly geriatric medicine and epidemiology.
Geriatric Medicine
It is important to review the literature of geriatric medicine.
Very good summaries on the impact of age on basic
mechanisms of the immune system (Murasko & Bernstein,
1999; Roth & Yen, 1999), cardiovascular system (Lakatta,
1999), and endocrine system (Gruenwald & Matsumoto, 1999;
Matthews & Cauley, 1999; Tenover, 1999), as well as major
diseases of aging that are studied in health psychology„
especially coronary heart disease (Wei, 1999), hypertension
(Applegate, 1999), diabetes (Halter, 1999), and Alzheimer•s
disease (AD; Kawas, 1999), can be found in Hazzard et al.•s
text (1999) on geriatric medicine. The 126 chapters of
this compendium provide an excellent source for the clinical
care of the aged and should be extremely useful for health psy-
chologists when working in an area with older persons as re-
search subjects or patients.
Geriatric medicine includes the full range of variation
seen at the end of the lifecycle. For some, life span continua-
tion is the norm, and the typical health psychology orienta-
tion by disease makes sense. For others, homeostasis has
broken down (see Siegler, 1989), and death appears to result
from nonspeci“c mechanisms (see Nuland, 1995), making
the search for behavioral correlates dif“cult.Epidemiology and Preventive MedicineFamiliarity with the epidemiological literature and training in
epidemiology, at some level, is very important for behavioral
scientists who work in aging and healthy psychology. You
need not be an epidemiologist to be suf“ciently well-versed in
epidemiological methods to bring these tools into your prac-
tice. Basic familiarity with epidemiological designs, method-
ological issues, and de“nitions provides useful tools for
research to health and psychologists and facilitates cross-
disciplinary communication. Epidemiological terms, also
sometimes used widely in medical research, are used incor-
rectly by psychologists. The termincidence(new cases over
some period of time) is often confused with prevalence
(number of cases at a designated time). Descriptions of designs
(e.g., case study, prospective cohort, retrospective cohort) are
often used incorrectly in the psychological literature. Psychol-
ogists should become familiar with these terms. A number of
texts offer this background (Fletcher, Fletcher, & Wagner,
1988; Hennekens, Buring, & Mayerent, 1987; Sackett, Haynes,
Guyatt, & Tugwell, 1991). Rothman•s work (1986, 1988) of-
fers an advanced exposure to methodological issues such as
subject selection, power calculation, and logistic regression
analysis (Hosmer & Lemeshow, 1998), while Larsen and
Shadlen (1999) provide an excellent chapter on who should in-
terpret screening diagnostics tests in individual cases.COGNITION AND NEUROPSYCHOLOGYResearch on cardiovascular disease and aging represents a
well-studied topic in health-aging research and serves as
a model for conceptual and methodological problems