Letters to the Editor
donal Classification of Diseases, Ninth Revision, Clinical
Modification (ICD-9-CM) code 820.8) were analyzed separately from the other types; in the US study, unspecified
hip fractures (ICD-9-CM codes 820.0) were grouped with
transcervical hip fractures (ICD-9-CM code 820.1). Validation of the Quebec data indicated that about 84 percent of
unspecified hip fractures were, in fact, transcervical. This
supports the groupings used by Karagas et al. (1).
Figure 2 shows a plot of the Quebec data revised to group
unspecified hip fractures with transcervical hip fractures.
With this grouping, the pattern of hip fractures for the
United States and Quebec is remarkably similar; rates increased rapidly with age and were higher among women
than men. The magnitude of rates of pertrochanteric hip
fracture was slightly lower in Quebec and, after including
unspecified fractures, rates of transcervical hip fracture
were also slightly lower in Quebec. For men, the ratio of the
two types did not change over age, and transcervical fractures were slightly less common than pertrochanteric fractures. For women, transcervical fractures predominate until
the eighth decade of life, after which the pattern is reversed.
These similarities and the parallelism in rates provide evidence that similar etiologic processes are operating in both
populations.
REFERENCES
1. Karagas MR, Lu-Yao GL, Barrett JA, et al. Heterogeneity of
hip fracture: age, race, sex, and geographic patterns of femoral
neck and trochantenc fractures among the US elderly. Am J
Epidemiol 1996,143:677-82.
2. Levy AR, Mayo NE, Grimard G. Rates of transcervical and
pertrochantenc hip fractures in the province of Quebec, Canada, 1981-1992. Am J Epidemiol 1995;142:428-38.
Adrian R. Levy
Nancy E. Mayo
Guy Grimard
Division of Clinical Epidemiology
Royal Victoria Hospital
687 Pine Ave. W., R4.29
Montreal, Quebec
Canada H3A 1A1
THE AUTHORS REPLY
We are grateful to Levy et al. (1) for their reanalysis of
the Quebec hip fracture data and for pointing out the dis-
803
tinction between our study (2) and their original analysis
(3). At the time we submitted our paper, their study had not
yet been published, and so it was not addressed in our paper.
This makes their comparison of the two studies especially
useful, and it is reassuring that the two analyses have similar
findings.
As noted by Levy et al., at issue is the interpretation of
International Classification of Diseases, Ninth Revision,
Clinical Modification (ICD-9-CM) c o d e s 8 2 0.8 and 820.9,
which include hip fracture not otherwise specified. Physician claims can clarify the actual fracture location in many
instances, providing an example of "internal" validation (4).
In our data, there were 5,570 hip fractures coded as ICD9-CM code 820.8 and 59 hip fractures as ICD-9-CM code
820.9. Of these, 3,592 had a physician claim which specified the location of the fracture: 3,107 (86.5 percent) indicated treatment of a femoral neck fracture, 446 (12.4 percent) had a physician claim for a trochantenc fracture, and
39 (1.1 percent) had both types listed. These data correspond with the results reported by Levy et al., and they
indicate that fractures coded as ICD-9-CM codes 820.8820.9 are very likely neck fractures.
REFERENCES
1. Levy AR, Mayo NE, Grimard G. Re: "Heterogeneity of hip
fracture: age, race, sex, and geographic patterns of femoral
neck and trochantenc fractures among the US elderly." (Letter) Am J Epidemiol 1996,144.801-3
2 Karagas MR, Lu-Yao GL, Barrett JA, et al. Heterogeneity of
hip fracture: age, race, sex, and geographic patterns of femoral
neck and trochantenc fractures among the US elderly. Am J
Epidemiol 1996;143:677-82.
3. Levy AR, Mayo NE, Grimard G Rates of transcervical and
pertrochanteric hip fractures in the province of Quebec, Canada, 1981-1992 Am J Epidemiol 1995,142:428-38.
4. Baron JA, Lu-Yao G, Barrett J, et al. Internal vahdauon of
Medicare claims data Epidemiology 1994;5:541-4.
Margaret R. Karagas
John A. Baron
Jane A. Barrett
Section of Epidemiology and Biostatistics
Department of Community and Family
Medicine
Dartmouth Medical School
Hanover, NH 03755-3861
RE: "MORTON LEVIN (1904-1995): HISTORY IN THE MAKING"
I was pleased that the Journal recently recognized the
passing of one of the "giants" of modem epidemiology,
Morton L. Levin (1). When Mort was being considered as
the fourth recipient of the John Snow Award of the Epidemiology Section of the American Public Health Association
in 1978, one of the members of the selection committee
remarked, ". . . . Mort Levin has had as much impact on
public health in this country as anyone during the past
quarter of a century" (quoted in reference 2). Thus, in
addition to his substantive and methodological contributions
to epidemiology, briefly described in the Journal obituary
(1), he made major contributions to public health in a
Am J Epidemiol
Vol. 144, No. 8, 1996
variety of areas. As assistant commissioner for medical
services in the New York State Health Department from
1947 to 1959, Levin pioneered the establishment of programs for the early diagnosis, treatment, and rehabilitation
of patients with cancer, diabetes mellitus, cerebral palsy,
and other chronic diseases; expanded the scope of statesupported cancer research; played a key role in the decision
to include a placebo-controlled, double-blinded, component
to the poliomyelitis vaccine field trials of 1954; and directed
the studies of the Commission on Chronic Illness to establish just what the burden of these diseases was on US
society in order to provide a scientific basis for the planning
804
Letters to the Editor
and implementation of appropriate public health interventions. Mort Levin was also a great teacher and an inspiration
to many, including the late Abraham M. Lilienfeld, who
credited Mort with arousing his interest in chronic disease
epidemiology. The life and work of Morton L. Levin deserve comprehensive documentation. In the meantime, readers of the Journal may find the following vignette revealing
of another facet of Mort Levin's character.
When the undersigned was an "apprentice epidemiologist" in the New York State Department of Health and
pursuing a master of public health degree at Columbia
University, the American Public Health Association met in
New York City. The year was 1949. At one of the meetings,
I fell into conversation with Dr. Levin. I had met him only
briefly during the previous year in the Department, but I
knew of his work and greatly admired him. On the spur of
the moment, I invited him to dinner at such a time when he
might be free during one of his frequent trips to the city. He
graciously accepted and a date was set. A few weeks later,
he came to our one-room apartment overlooking an air shaft
on West 87th Street I had anticipated an evening of reminiscences of epidemiologic investigations and discussion of
current issues. Instead, the conversation never touched on
epidemiology; the subjects were J. S. Bach, Albert
Schweitzer, and the Irish Poets. The conversation was between Mort and my wife.
REFERENCES
1 Armenian HK, Szklo M. Morton Levin (1904-1995): history
in the making Am J Epidemiol 1996;143.648-9.
2 Winkelstein W Jr. Introductory remarks of Warren Winkelstein Jr. on the occasion of the presentauon of the 1978 John
Snow Award of the Epidemiology SecUon of the American
Public Health Association to Morton L. Levin, Los Angeles,
CA, October 18, 1978.
Warren Winkelstein, Jr.
Division of Population Biology and
Epidemiology
School of Public Health
University of California
Berkeley, CA 94720-7360
Editor's note: In accordance with Journal policy, Drs.
Armenian and Szklo were asked if they wished to respond to
the above letter from Dr. Winkelstein, but they chose not to
do so.
RE: "MAGNETIC FIELDS AND CANCER IN CHILDREN RESIDING NEAR SWEDISH HIGH-VOLTAGE
POWER LINES"
In reply to questions raised by Dr. Richard G. Stevens (1)
in regard to their study on magnetic fields and cancer in
children residing near Swedish high-voltage power lines
(2), Feychting and Ahlbom (3) referred to their linear correlations of field strength with inverse-squared distance
from power lines. They pointed out that with R2 = 0.62, for
correlation coefficient R, this means 62 percent of the variance is explained, but that there is a mixture of 220 kV and
400 kV lines.
A combination of data from two perfect linear correlations could easily reduce R2 to 0.62 when mixed together.
If we take data at independent variable values xh
i = 1, .... n with dependent variable values perfectly correlated on two lines, y = kxx and y = k2x, we have the
2n points (x,, k^ x,), (xn k2x,). We can then show that
R2 = B(n - A)/(2n -
AB),
where
y = kj x for j = 1, ..., m, the result above extends to a
general formula for mixed correlations:
R2 = C(n - A)/(mn - AC),
where
C =
summed7 = 1 ... m.
We can further show that 1 < A < n and 1 < C
< m for positive distinct values of x, and of kJt and that R2
spans the whole range from 0 to 1. A simple choice of data
which are severally perfectly correlated with a moderate
variation in the k can easily pull R2 down to 0.1.
The moral is that if you mix data from good correlations
with different slopes, expect a poorly correlated result.
Distance from power lines will, however, be a good indicator of time-averaged fields from lines of similar rating and
average loading.
REFERENCES
A =
summed/ = 1 ... n,
= (*, + *2) 2 /0tl 2 + * 2 2 )-
Taking five equally spaced values x, = i and one line
slope as twice the other, i.e., k^ = 2k2, gives R2 = 0.62.
In practice, the line slopes may not be in the ratio 2:1,
particularly for magnetic fields, which depend on current
rather than voltage. But the strength also depends on the
power load of the line, which varies substantially from time
to time, by more than a factor of 2.
If we consider the various field strengths to be like
a mixture of several different correlation lines,
1. Stevens RG. Re: "Magnetic fields and cancer in children
residing near Swedish high-voltage power lines." (Letter).
AmJ Epidemiol 1994; 140:75.
2. Feychting M, Ahlbom A. Magnetic fields and cancer in children residing near Swedish high-voltage power lines. Am J
Epidemiol 1993,138:467-82.
3. Feychting M, Ahlbom A. Re: "Magnetic fields and cancer in
children residing near Swedish high-voltage power lines."
(The Authors Reply). Am J Epidemiol 1994; 140:75.
M. J. O'Carroll
Langhope Tower, Ryhope Road
University of Sunderland
Sunderland SR2 7EE
England
Am J Epidemiol
Vol. 144, No. 8, 1996