Vol 103, No 6
AMERICAN JOURNAL OF EPIDEMIOLOGY
Copyright © 1976 by The Johns Hopkins University School of Hygiene and Public Health
Printed in U.SA.
ASSOCIATIONS OF CORONARY AND STROKE MORTALITY WITH
TEMPERATURE AND SNOWFALL IN SELECTED AREAS OF
THE UNITED STATES, 1962-1966
EUGENE ROGOT AND STEPHEN J. PADGETT 1
coronary heart disease; mortality; stroke; weather
Speculation on the effects of climate
upon health goes back at least to Hippocrates and his "Air, Waters and Places"
(1). Only in recent years, with the careful
and complete recording of vital and medical events and the weather, has it been
possible to relate on a daily basis such
figures as deaths from disease to average
temperature for a city. Some of the earliest
studies in the United States in which daily
mortality and weather data were used
appear to have been those of Justin (2) and
of Huntington (3), who both covered mortality and weather in New York City for the
years 1882-1888. More recently, studies in
temperate climates here and abroad (4-11)
have shown the characteristic pattern for
total mortality and for cardiovascular mortality to be one with high mortality in the
winter and low mortality in the summer.
Exceptions to the usual pattern are the
studies by Heyer et al. (12), reporting
increased frequency of acute myocardial
infarctions in the summer in Dallas, Texas;
DePasquale and Burch (13) reporting similarly for New Orleans, Louisiana; and Avierinos (14) with similar findings for Cairo
and all of Egypt.
The present study is a sequel to studies
of cardiovascular mortality as related to
weather in Memphis for 1959-1961 (15)
and in Chicago for 1967 (16, 17). In both
studies the weather variable most strongly
associated with coronary heart disease
(CHD) mortality was the daily average
temperature.
In Chicago, an inverse linear relationship
was observed between temperature and
CHD deaths. Snowfall also appeared to be
an important factor. With temperature
Received for publication August 15, 1975, and in
final form October 29, 1975.
Abbreviations: CHD, coronary heart disease;
SMSA, standard metropolitan statistical area.
1
Epidemiology Branch, Division of Heart & Vascular Diseases, National Heart & Lung Institute, NIH,
Landow Building, Room C-825, Bethesda, MD 20014.
The authors thank Robert W. Buechley and John
B. Van Bruggen for providing the basic tapes, and
Charles E. Sydenstricker for invaluable programming
help in the early stages of this study.
565
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Rogot. E.. and S. J. Padgett (NHLI. NIH. Bethesda. MD 20014). Associations of coronary and stroke mortality with temperature and snowfall in selected areas of the United States. 1962-1966. Am J Epidemiol 103:566-575.
1976.
Daily temperatures and snowfall were related to coronary and stroke deaths
in selected standard metropolitan statistical areas for the 5-year period
1962-1966. Typically an inverse approximately linear pattern of coronary heart
disease (CHD) and of stroke mortality with temperature was seen over the
greater part of the temperature range, with mortality reaching a low for days
with average Fahrenheit temperatures in the 60's and 70's (15.6-26.6 C). and
then rising sharply at higher temperatures. Snowfall was found to be associated
with higher CHD and stroke mortality for a 5- or 6-day period. Temperatures 1
and 2 days prior to death were also found to be associated with deaths from
CHD and stroke. Very hot days appeared to exert a cumulative effect upon
mortality in many of the areas.
566
ROGOT AND PADGETT
sen. Next, high snowfall areas with moderately large populations were chosen. Here
it seemed appropriate to include SMSA's
fairly close to one another. Next, areas with
hot climates and of moderately large size
were chosen. Here again, several areas
fairly close to one another were included.
A number of areas were then chosen in an
attempt to improve the geographic representation of the United States. Finally,
certain areas were chosen because of their
unique climates. In all, the 32 SMSA's
included about 40 per cent of the US
population.
RESULTS
Figure 1 shows average numbers of CHD
deaths per day for each area according to
MATERIALS AND METHODS
200
Mortality data for the United States for
the five years, 1962-1966, were made available to us by the National Center for
Health Statistics (NCHS). This is the most
recent period in which day of death was
coded by the NCHS. The causes studied in
this paper are CHD (ICD #420, 7th Revision) and stroke (ICD #330-334, 7th Revision).
A total of 32 standard metropolitan statistical areas (SMSA's) were initially
chosen for study. Resident deaths in these 8 "
areas with underlying cause of death given 3
as either CHD or stroke were selected. The B 1
choice of an SMS A rather than a city as the
basic unit of study seemed appropriate
i •
since these mortality data were available
and temperature and snowfall data as
reported by the Weather Bureau for the
central city in the SMSA could be used to
cover the entire SMSA. The areas chosen
for study are given in table 1, along with
the total number of CHD and stroke deaths
in the five year period, the average daily
-20
0
20 40
EO BD 100
0 20 U SO 10 UD F
temperature and numbers of snowfall days.
-S -U
-7
4
16
27
X
-o -7 4 ii n a c
The 32 areas were chosen from the 201
AVBWH laOBUTUBE ON OAT Of DEATH
SMSA's designated in the 1960 census as
FIGURE 1. Average daily deaths from CHD by
follows: First, the largest areas, those with average temperature on day of death for 32 selected
more than 1 million population, were cho- SMSA's: US, 1962-1966.
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controlled, positive associations were noted
for CHD deaths and snowfall. The patterns
observed for temperature and snowfall held
mainly for men.
For stroke deaths, no clear-cut relationship to the daily temperature emerged in
Chicago, although in Memphis an inverse
relationship had been reported.
A number of questions raised in the
above studies suggested a study of more
areas for longer periods of time. The major
goals of the present study] are to investigate
the association of CHD deaths, and of
stroke deaths, with daily temperature and
snowfall in selected standard metropolitan
statistical areas over a five year period, and
to explore associations by sex, age and
area.
567
WEATHER AND CORONARY AND STROKE MORTALITY
Overall, these graphs are remarkably
consistent by area. An inverse approximately linear (or log-linear) pattern of
CHD mortality with temperature is seen
over the greater part of the temperature
range with mortality reaching a low for
days with average Fahrenheit temperatures in the sixties and seventies (15.6-26.6
C), and then rising sharply. This pattern
holds for 15 of the 17 snow areas (Denver
and Salt Lake City are the exceptions).
Excepting Honolulu and possibly Memphis the warmer areas show the same basic
pattern. However, for the warmer areas,
the low mortality point occurs at 80-89 F
TABLE 1
Deaths from CHD and stroke, average daily temperature and number of snowfall days for 32 selected SMSA's'
US, 1962-1966
SMSA
Atlanta
Boston-Lowell-Lawrence
Buffalo
Chicago
Cleveland
Dallas
Denver
Detroit
Honolulu
Houston
Los Angeles-Long Beach
Memphis
Miami
Milwaukee
Minneapolis-St. Paul
New Orleans
New York
Omaha
Philadelphia
Phoenix
Pittsburgh
Portland, Oreg-Wash
Rochester
St. Louis
Salt Lake City
San Antonio
San Diego
San Francisco-Oakland
Seattle
Syracuse
Tampa-St. Petersburg
Washington, D.C.-Md.-Va.
Average daily F(C)
temperature
Days under 40 F
Stroke
5,969
16,697
6,547
28,863
8,655
5,530
3,978
16,237
1,026
4,837
36,450
4,520
4,665
6,450
8,317
4,318
44,064
2,397
20,006
2,715
13,788
6,077
3,253
11,347
1,499
2,769
4,498
13,503
6,413
2,984
7,466
7,500
60(15.6)
51 (10.6)
47 (8.3)
51 (10.6)
49 (9.4)
66(18 9)
50(10.0)
50 (10.0)
77 (25.0)
70 (21.1)
62(16.7)
62 (16.7)
76 (23 9)
46 (7.8)
44(6 7)
68 (20.0)
55 (12.8)
52(11.1)
53(11.7)
70(21.1)
50(10 0)
53(11.7)
48 (8.9)
55 (12.8)
51 (10.6)
69 (20.6)
63(17.2)
56(13.3)
54(12.2)
47 (8.3)
72 (22.2)
57 (13.9)
11
135
344
168
254
15
158
175
Deaths from
CHD
10,715
57,257
24,585
118,001
29,006
12,552
11,895
52,216
2,999
13,511
88,734
6,865
15,867
17,897
20,576
13,665
212,606
7,016
68,886
8,453
44,514
14,466
11,328
34,118
3,540
6,876
12,654
41,854
16,511
10,838
16,722
21,668
{A A C*\ with
\t i \jf witn
snowfall
20
189
184
1
81
132
78
221
12
289
62
164
4
1
24
318
61
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the average (mid-range) temperature in
10-degree units Fahrenheit (equivalent to
5.6-degree units centigrade) on the day of
death. The 17 areas on the left side of figure
1 are considered our "snow areas," with
snowfall days ranging from 61 in Washington, D.C. to 344 in Buffalo (table 1). By
contrast the 15 areas on the right side experienced few if any snow days over the
five-year period. The vertical scale in figure
1 is logarithmic to allow for direct comparisons between areas of relative changes and
to present a more compact set of graphs.
The numbers of days by temperature
ranges for each area are given in table 2.
568
ROGOT AND PADGETT
TABLE 2
Frequency distribution of days by daily average temperature 32 selected SMSA's, US, 1962-1966
DayB by daily average temperature
SMSA
10 to
19
20 to
29
30 to
39
40 to
49
50 to
69
60 to
69
70 to
79
80 to
89
,«> Below - 2 2 to - 1 7 to
(C)
-12
-22
-18
- 1 1 to
-7
- 6 to
-1
Oto
3
4to
9
10 to
15
16 to
20
21 to
26
27 to
31
7
57
116
92
94
5
61
102
34
170
206
168
179
25
177
191
167
302
310
261
290
99
231
287
289
323
284
249
270
216
341
255
304
305
274
242
288
273
295
261
6
39
128
32
253
5
253
202
175
343
247
316
153
298
562
289
249
294
162
8
309
520
273
44
310
253
627
285
57
273
254
273
290
237
292
411
276
502
272
263
300
275
596
863
605
281
217
287
352
366
373
311
360
309
372
348
45
362
913
292
277
343
337
347
320
312
319
307
377
458
363
285
290
339
912
609
537
353
412
282
588
263
215
342
284
403
294
291
1250
461
241
445
841
224
230
583
378
366
337
322
302
101
229
435
287
409
301
38
58
235
696
396
84
36
10
100
23
422
17
65
531
573
11
306
646
27
43
404
87
117
86
387
16
2
21
140
95
572
8
2
4
5
29
1
-1
1
17
5
1
4
37
42
33
8
2
26
24
6
9
63
161
33
65
51
102
120
123
19
1
43
4
28
112
39
206
206
8
120
153
146
3
24
1
3
5
37
24
8
90
4
116
56
66
291
245
36
257
218
287
13
273
185
299
226
273
50
6
40
166
12
199
135
208
7
1
115
8
202
20
89
(26.7-32.1 C) for Miami, Tampa, Houston
and Phoenix. Also, there was no upturn in
mortality at the hot temperatures for
Miami and Tampa.
Figure 2 presents stroke deaths versus
temperature for the 32 areas, as in figure 1.
We note first that the numbers of stroke
deaths in each area are much smaller than
the numbers of CHD deaths, and for this
reason alone, underlying patterns for
stroke would be more affected by random
fluctuation than those for CHD. In general,
the patterns seen for stroke are quite simi-
7
97
295
5
261
90+
on .
SZ +
74
4
2
6
2
2
233
10
12
1
26
552
181
lar to those described for CHD. The main
differences are for mortality at the coldest
temperatures. Considering just that portion of each curve for days with average
temperature under 40 F (under 4.4 C), six
of the 17 snow areas showed peak mortality
at their lowest temperature points and six
showed peak mortality at their second
lowest points. The corresponding numbers
for CHD were 15 and 1, respectively. For
the warm areas, this distinction between
stroke and CHD is not as evident.
At higher temperatures, comparing fig-
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Atlanta
Boston
Buffalo
Chicago
Cleveland
Dallas
Denver
Detroit
Honolulu
Houston
Los Angeles
Memphis
Miami
Milwaukee
Minn-St.Paul
New Orleans
New York
Omaha
Philadelphia
Phoenn
Pittsburgh
Portland
Rochester
St. Louis
Salt Lake
San Antonio
San Diego
San Francisco
Seattle
Syracuse
Tampa
Washington
-9 to
Oto
9
,^1 Below
(F)
_9
1
569
WEATHER AND CORONARY AND STROKE MORTALITY
0
-28-1
8
-7
«»
4
60
IS
JO 100
27 31
0
-«
20
-7
40
4
Snowfall day
Days after most recent snowfall
1
2
3
4
5
6
II
27
I
C
CHD
17
Stroke
15
15
13
12
10
9
8
14
16
15
15
13
9
Note that each entry here is an independFIGURE 2. Average daily deaths from stroke by ent statistic, and under the null hypothesis
average temperature on day of death for 32 selected that snow and mortality are not associated,
each statistic has an expected value of 8.5.
SMSA's: US, 1962-1966
Using the control averages, we calcuure 1 with figure 2, there is a tendency for lated expected numbers of deaths in each
areas to experience even sharper rises in of the other categories by multiplying the
mortality for stroke than for CHD. This number of days in a given category by the
tendency appears to be especially pro- control average. These expected numbers
nounced for the larger SMSA's. It may also can be compared to the observed numbers
be seen in figures 1 and 2 that warmer areas of deaths to measure the effect of the
tend to show greater mortality excesses on snowfall. These results are summarized in
cold days than do colder areas. Similarly, figure 3. Since days of and following snowcolder areas tend to exhibit greater mortal- fall tend to be somewhat colder than the
ity excesses on hot days than do warmer other days under 40 F, the data were also
areas. It should be noted that the right- adjusted for temperature. (The method of
most and leftmost points of figures 1 and 2 adjustment is described in the footnotes to
in many areas may be based on small num- table 3.) In the case of stroke, no noticeable
bers of deaths and days.
change was observed. In the case of CHD,
Of the 32 SMSA's, 17 were studied for values for the excesses were in almost every
possible effects of snowfall upon mortality. instance smaller by amounts from .01
These are the areas on the left side of to .02.
figures 1 and 2. Preliminary analyses indiBoth figure 3 and the text table above
cated positive associations between snow- show that snowfall is related to mortality
fall and mortality for the day of the snow- on the day of the snowfall and for several
fall and for several days afterward. As a days after. For stroke there is a substantial
AVBWE TWBUTURE ON MY Of DEATH
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on March 5, 2016
result we calculated mortality averages on
days under 40 F (under 4.4 C) for the
following non-overlapping categories of
days: day* with snowfall; days 1, 2, 3, 4, 5
and 6 following the most recent snowfall;
and 7 or more days following the most
recent snowfall. The average daily mortality (for each area) for the group 7 or more
days'from any snowfall was used as "control," i.e., the average for days under 40 F
unaffected by snowfall.
The number of areas (out of 17) for which
the mortality averages in the first 7 categories were in excess of the control average
were as follows:
570
ROGOT AND PADGETT
days under 40 F which follow most recent
snowfall by six or more days. Ratios of O to
E are given in table 3.
For both diseases, almost all SMSA's
show mortality excesses during the snow
periods—CHD in Denver was the only
exception. Out of 17 cities, 10 show statistically significant excesses for CHD and 11
SI UK
iE
TABLE 3
0
1 2
3
4
5
6
0
1 2
3
4
5
M Y ABB) MOST RHHfT SNOWFAU
For Oqn Wift A m p T m p n l i n i Unda 40 F (4.4 a
SMSA
FIGURE 3. Mortality excesses for CHD and stroke in
17 SMSA's on days of and after snowfall by amount of
snowfall: US, 1962-1966. O
O, light snow ( < 1 Boston
inch; <2.54 cm); A
A, medium snow, (1-4.9 Buffalo
inches; 2.54 cm-12.7 cm); A
• , heavy snow (5+ Chicago
Cleveland
inches; >12.7 cm).
O = total observed deaths over 17 SMSA's; E = Denver
total expected deaths over 17 SMSA's based on Detroit
averages for days under 40 F which follow snowfall by Milwaukee
at least 7 days. Points are not shown for "heavy snow, M i n n - S t P a u l
days 3, 4, 5 and 6 since not all 17 areas had days in New York
Omaha
these categories.
Philadelphia
Pittsburgh
and uniform mortality excess lasting from Rochester
the day of the snowfall until five days after. St Louis
However, mortality appears to be related Salt Lake
only weakly to amount of snowfall. For Syracuse
Washington
CHD, there is a substantial mortality ex- Total §
cess on the day of the snowfall and on the Total (temperature
adjusted) |
first day after. For two through four days
after snowfall, CHD shows weak but statistically significant association. CHD mortality is strongly related to amount of
snowfall.
To summarize the association of snow
with CHD and stroke, we tabulated observed (O) deaths and calculated expected
(E) numbers of deaths on days under 40 F
during a six-day snow period—includes
snowfall day and days 1, 2, 3, 4, 5 after
most recent snowfall. A five-day snow period would have been sufficient for CHD,
but six was used in order to make direct
comparison with stroke. Expected numbers were based on mortality averages of
CHD
O/E
£
1.09*
1.02
1.07*
1.10*
.97
1.03
106*
104*
1.04*
1.15*
105*
1.06*
1.11
1.07*
1.09
1.01
1.02
1.056
1.034
1 .11*
1 .06
1 .07*
1 11*
1 .19*
1 .08*
] .17*
1 .08*
] .04*
L.04
O/E
L.02
] 13*
1L.ll
] .02
L 18
1.36*
L.07*
L.084
L.092
penodf
369
603
433
502
378
459
498
535
245
349
252
449
542
207
403
572
192
* E based on daily mortality averages of days under
40 F which follow the most recent snowfall by 6 or
more days
t Snowfall period includes snowfall days and days
1, 2, 3, 4, 5 after most recent snowfall.
* Statistically significant at .05 level.
§ Total ratio is found after O and E were accumulated over all areas. No statistical tests of significance were done on totals.
I Each area was adjusted separately by an indirect
method using for standard "rates" the average daily
deaths for days following the most recent snowfall by
6 or more days. Temperature categories used were:
less than 20 F, 20-29 F and 30-39 F (less than - 6 . 7 C,
- 6 . 7 through - 1 . 2 C and - 1 . 1 through 4.3 C). The
adjusted values of E were accumulated over all areas
in order to find the adjusted total O/E.
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0
•JE
Ratios of observed (O) to expected (E)* numbers of
CHD and stroke deaths for days under 40 F (4.4 C)
during the 6-day snow period, 17 SMSA's. US,
1962-1966
571
WEATHER AND CORONARY AND STROKE MORTAUTY
Stroke
A
B
C
D
E
-
Average temperature <40F with snowfall
Average temperature <40F with no snowfall
Average temperature 40-59 F (4 4-15 5 C)
Average temperature 60-79 F (15.6-26.6 C)
Average temperature 80 F + (26.7 C+)
Next, each day was classified according to
its temperature-snowfall and the temperature-snowfall of the day before. This gives,
theoretically, 25 possible kinds of days—
AA, AB, A C , . . . , DE, EE, with the first
letter indicating the weather of the previous day and the second the weather of the
current day. Similarly, we may consider
one day's weather as made up of the
temperature-snowfall of that day and the
two previous days. Each day can then be
represented by a three-letter group such as
AAA, AAB, etc., with the initial letter
denoting the weather two days ago, the
second letter indicating yesterday's
weather and the third letter indicating today's weather. Table 4 presents summary
data for the simplest case (A, B, C, D, E
days); table 5 shows data for selected pairs
and table 6 for selected three-letter groups.
The areas were divided as shown in tables 4
and 5 on the basis of similarity of temperature ranges (see table 2). The figures shown
are averages of index numbers which were
prepared initially for each area. The index
numbers for a given area were calculated
by dividing the average deaths per day for
each weather category by the average
deaths per day over the five-year period for
that area, and multiplying the result by
A
B
C
D
E
108
105
98
95
116
122|
107
97
99
105
103
93
107
96
121
102
94
•A - Average temperature <40 F (<4.4 C) with
snowfall.
B «. Average temperature <40F with no snowfall.
C - Average temperature 40-59 F (4.4-15.5 C).
D - Average temperature 60-79 F (15.6-26.6 C).
E - Average temperature 80 F+ (26.7 C + ) .
f Index numbers were first calculated for each area
by dividing the average daily CHD (and stroke)
deaths in given weather categories by the average
daily CHD (and stroke) deaths in the 5-year period
and multiplying by 100. Averages were then obtained
by summing the appropriate index numbers and
dividing by the number of areas in the group.
| Includes Boston, Buffalo, Chicago, Cleveland,
Denver, Detroit, Milwaukee, Minneapolis, New York,
Omaha, Philadelphia, Pittsburgh, Rochester, St.
Louis, Salt Lake, Syracuse and Washington, D.C.
} Includes Atlanta, Dallas, Houston, Memphis,
Miami, New Orleans, Phoenix, San Antonio and
Tampa.
I Based on 8 areas.
100. Index numbers based on less than 20
deaths were not included in calculating
averages. The averages obtained give
equal weight to each area.
The data in table 4 recapitulate much of
the previous material. For the 17 snow
areas, for CHD and for stroke, we have
A > B > C > D and D < E . For the nine
warm areas we have B > C > D > E for
CHD; for stroke, B > C > D butD <E. Port-
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TABLE 4
for stroke. The totals indicate that overall,
stroke mortality is affected relatively more Average index numbers for CHD and stroke deaths by
weather on day of death for selected groups of
than CHD. Temperature adjustment reSMSA's- US, 1962-1966
sults in a reduction in the overall excess for
Average index numberet for
CHD but not for stroke. Thus some of the Average
mortality excess for CHD during the snow atureand
Los
Portland,
Angeles, HonoSan
snowfall 17 snow 9 warm
period may be due to colder temperatures.
San
on day areas}
areas}
Francisco.
lulu
Diego
Seattle
Since snowfall was associated with ofdeath*
higher CHD and stroke mortality for a 5- or
CHD
6-day period, we decided to study the
A
112
possible prolonged effects of cold or hot
B
108
1211
106
107
103
110
100
C
days upon mortality as well. For this pur96
D
93
102
98
93
pose each day was first classified into one
116
E
96
104
95
of five broad categories:
572
ROGOT AND PADGETT
TABLE 5
TABLE 6
Average index numbers for CHD and stroke deaths by
type of weather on day of death in terms of yesterday's
and today's average temperature and snowfall, for
selected groups of SMSA's US, 1962-1966
Average index numbers for CHD and stroke deaths by
type of weather on day of death in terms of average
temperature and snowfall 2 days ago, yesterday and
today: 17 SMSA's, US, 1962-1966
Average
Portland,
Los
Angeles, HonoSan
temperature 17 enow 9 warm
and snow- areas
San
lulu
areas Francisco,
fall on day
Diego
Seattle
of death*
CHD
AC
108t
BC
CC
DC
104
100
95
98
93
100
101
109*
CD
DD
ED
DE
EE
AA
BA
CA
AB
BB
CB
AC
BC
CC
DC
CD
DD
ED
DE
EE
110
105
104||
108
105
102
110**
104
98
95
98
94
107
112
128t
123}
1191
108
105
1201
112
106
107
98
91
93
95
Stroke
113
103
93
97
93
1208
1201
112ft
1131
107
102
108
96
96
98
100
100
104
96
93
93
107
107
106
95
111
95
132
104
84
89
96
107
109
104
95
129**
124**
151**
39
140
76
98
101
* See table 4 for list of areas, description of weather
categories A, B, C, D, E and average index numbers
Each pair of letters is taken as a single day with a
weather component from yesterday (the first letter)
and a weather component from today (the second
letter) and is related to deaths today.
t Based on 14 areas
* Based on 15 areas
§ Based on 6 areas.
H Based on 7 areas
I Based on 16 areas.
*• Based on 12 areas
f t Based on 2 areas.
** Based on Los Angeles only.
AAA
BAA
ABA
BBA
CBA
CCA
AAB
BAB
ABB
BBB
CBB
BCB
CCB
BBC
CBC
BCC
CCC
DCC
CDC
DDC
CCD
DCD
CDD
DDD
EDD
DED
EED
DDE
DEE
EEE
CHD
Stroke
116
114
111
110
114f
110
114
110
106
105
102
106*
100
104
103*
104
100
95
99
94
99
94
99
92
92
96
105f
101
108f
112}
114*
106
HO*
106
1091
1051
108
110
111
104
97*
100*
103
102
107*
109
96
93
96*
93
98
96*
99
93
97
102*
110"
112
124}
132**
* See table 4 for list of areas, description of weather
categories A, B, C, D, E and average index numbers.
Each 3-letter group is taken as a single day with a
weather component from 2 days ago (the first letter),
a weather component from yesterday (the second
letter) and a weather component from today (the
third letter) and is related to deaths today
t Based on 15 areas.
* Based on 16 areas.
} Based on 12 areas.
1 Based on 10 areas.
I Based on 13 areas
*• Based on 11 areas.
land, San Francisco and Seattle show
B>C>D for both CHD and stroke. Los
Angeles and San Diego resemble the snow
areas in that O D but D<E.
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AB
BB
CB
114
111
110
110
105
102
AA
BA
CA
Average temperature
and snowfall on day
ofdeath*
573
WEATHER AND CORONARY AND STROKE MORTALITY
tutes more or less favorable mortality days
but this is beyond the scope of the present
paper.
The data so far have dealt only with total
CHD or stroke deaths. We are also interested in describing associations according
to age and sex. Material similar to tables
4-6 was prepared separately for males,
females, ages under 65 and ages 65 and
over. A portion of these results—those for
the 17 snow areas—is given in table 7. For
CHD, the main pattern is seen to be
essentially the same by sex and by age,
although the excess for snowfall days compared with other cold days (A vs. B days) is
more pronounced for males than females
and for ages under 65 compared with ages
65 and over.
For stroke deaths, table 7 shows that the
largest excesses occur during the very hot
E-days for all groups, with the excess more
pronounced for females than males, and for
the 65+ ages compared with those under
65. Unlike CHD, there is no observed
excess for snowfall days compared with
other cold days (A vs. B days) for males,
although a substantial difference is noted
for females.
The main results described above for
temperature and snowfall were examined
separately by year for the larger areas and
appeared to be consistent from year to
year.
TABLE 7
Average index numbers for CHD and stroke deaths by weather on day of death and sex, and by weather on day
of death and age (in years)- 17 SMSA's, US, 1962-1966
Average
temperature
and enow- —
fall on day
Male
ofdeath*
A
B
C
D
E
113
105
99
94
105
CHD
Stroke
Female
<66
65+
Male
Female
<65
65+
109
107
100
92
104
111
103
98
97
108
112
107
100
92
103
105
106
99
95
110
105
97
95
124f
108
105
99
96
107
106
98
95
120
116t
109*
* See table 4 for list of areas, description of weather categories and average index numbers,
t Based on 15 areas.
X Based on 9 areas.
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on March 5, 2016
CHD and stroke show similar overall
patterns but differ in that highest mortality usually occurs for CHD on the coldest
days while for stroke highest mortality may
occur on the hottest days. For the 17 areas,
average index numbers range from 93 for D
days to 112 for A days for CHD and from 95
on D days to 116 on E days for stroke.
Table 5 shows that yesterday's weather
is associated with deaths today from CHD
and stroke. Thus, for the 17 snow areas,
controlling on today's weather, we have
AA>BA>CA, AB>BB>CB, A C > B O C C
>DC, CD>DD but ED>DD and EE>DE.
Average index numbers range from 93 on
DD days to 115 on AA days for CHD and
from 94 on DD days to 128 on EE days for
stroke.
Controlling on yesterday's as well as
today's weather, table 6 indicates that the
weather two days ago is also associated
with today's mortality but the associations
are not as consistent as before. Thus, for
the 17 snow areas (for CHD and for stroke),
ABB > BBB > CBB and BCC > CCC > DCC
but CBA>BBA. For these areas, the average index numbers range from 92 on DDD
days to 116 on AAA days for CHD and from
94 on DDD days to 132 on EEE days for
stroke.
Studying longer weather strings involving the previous three, four or more days
may yield further insights into what consti-
574
ROGOT AND PADGETT
DISCUSSION
Downloaded from http://aje.oxfordjournals.org/ at Pennsylvania State University on March 5, 2016
Of the several results in this study, the
most important we believe is the inverse
relationship between temperature and
mortality which prevails over most of the
temperature range. The idea that extremely cold weather has an adverse effect
upon people, sick or well, is easily appreciated. Many studies have in fact shown that
excess mortality occurs when the weather
is very cold. Not so evident and certainly
not as well known is the greater mortality
occurring at the more moderate temperatures of 40-49 F (4.4-9.9 C) compared with
50-59 F (10.0-15.5 C), or that of 50-59 F
compared with 60-69 F (15.6-21.0 C). Further, this inverse relationship is remarkably consistent from area to area. The main
differences between areas seem to be the
exact temperature grouping at which mortality is lowest, and whether in fact an
upturn in mortality is realized at the very
high temperatures. The fact that the
"ideal" temperature is somewhat higher
for the warmer areas seems reasonable.
This suggests that a relative as well as an
absolute level of temperature is important,
and that an overall physiologic adjustment
or adjustment in life style to the local
climate occurs.
In theory, the relationship between mortality and temperature might be visualized
as a U-shaped function with mortality
rising very sharply during extremely cold
and extremely hot weather. A hint of this is
present mainly for some of the colder areas
for CHD.
The fact that stroke deaths do not show
any consistent pattern at the colder temperatures is not understood. One possibility may be that with stroke, since there is
on the average a longer period between onset and death than with CHD, and since
there are relatively few days at the coldest
temperatures, there may be a masking of
the underlying effect as a given stroke
death may be associated with the tempera-
ture of a day several removed from the day
of onset. If the day of onset were in the
coldest temperature grouping, the day of
death could easily fall into a higher temperature grouping. This would be less apt to
happen for CHD since a high proportion
of CHD deaths are "sudden," occurring
within one hour of onset (18). We also have
the prolonged effects of snowfall upon
stroke deaths which may confuse the picture.
The excess of CHD mortality associated
with snowfall was anticipated. The results
agree with previous findings reported for
Chicago for 1967 (16, 17) and with a recent
Japanese report (19) on hospitalized cases
of myocardial infarction. As far as we know
there is no other literature on this subject.
The finding of excess mortality from
stroke associated with snowfall was unexpected. Yet more surprising was the finding that overall, the per cent excess for
stroke was greater than that observed for
CHD. However, CHD mortality was much
more strongly related to amount of snow
than was stroke. This suggests that factors
associated with snow rather than snow
itself may be responsible for the increase in
stroke mortality during the snow period.
There is a widespread clinical impression
that shoveling snow may set off a heart
attack. We know of no similar claim for
stroke. In any event, this study provides no
data bearing directly on these points.
An interesting finding worth noting in
the present study is the apparent cumulative effect of the very hot days upon
mortality, in most of the colder areas and
in Los Angeles and San Diego. Thus, for
example, average index numbers for CHD
over the 17 snow areas were 101, 108 and
112 and for stroke 112, 125 and 132 for
DDE, DEE and EEE-days, respectively
(table 6). The question arises, "For how
many days does a cumulative effect persist?" A full study of this question is
beyond the scope of the present study. A
special study of New York and Chicago in
WEATHER AND CORONARY AND STROKE MORTALITY
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this respect showed that the excess mortality built up for about a week and then
declined.
The ideal temperature of 60-79 F
(15.6-26.6 C), at which lowest mortality
generally occurs, corresponds with what
many people consider to be pleasant temperatures. Possibly such days are considered pleasant because the cardiovascular
system is functioning at its optimum. Evidently, any departure from an "ideal day"
constitutes a threat—sufficient in some
instances to kill. Some of the observed
excesses in mortality are no doubt due to
terminal or very seriously ill heart or stroke
patients succumbing in bad weather, the so
called "harvesting effect." However, there
may also be a concomitant increase in
incidence of disease, and in severity of
disease, as well. These increases must also
contribute to the observed excess mortality
in bad weather. In support of this we have a
number of studies in which hospital admissions were related to the weather or season
of the year: for example, the studies of Rose
(7), Bull (8), Doring and Loddenkemper
(10) orYamazaki (19).
We visualize a simple process in which
bad weather, defined as average daily temperature outside the ideal range, exerts an
adverse effect upon everyone whether
healthy or sick. In the case of CHD, new
disease may develop and result in sudden
death that day, in death the next day or
several days later. An increase in severity
of disease could also occur and result in
death that day or in the next several days.
Such events could be directly attributable
to the weather. In the case of stroke, a
similar situation may prevail but with
relatively fewer sudden deaths and relatively more prolonged effects due to the
weather.
575