MALARIA SURVEY—METHODS AND PROCEDURES 
299 
should be considered together. An analy¬ 
sis of the survey data gives information on 
various subjects: (1) the scope of the ma¬ 
laria problem in the community, (2) the 
intensity of the malaria problem, (3) the 
vectors involved and their areas of produc¬ 
tion, (4) consideration of control measures 
which are applicable, (5) preparation of a 
control project. 
The perforated cards pertaining to each 
geographical unit should be analyzed 
separately. From these cards information 
is quickly tabulated showing: the age, sex, 
and race groups of those examined; the 
numbers with splenomegaly in each of the 
above groups, as well as the total j 1 the inci¬ 
dence of parasitemia in each spleen group; 
and the incidence of splenomegaly in each 
geographical subdivision. 
An index of malarial infection may be 
determined by choosing some criterion for 
infection and determining the number of 
persons satisfying the criterion per 100 or 
1000 of the sample examined. Since no 
one criterion will infallibly reveal all cases 
of infection, the computed index of infec¬ 
tion will almost invariably be too small. 
In case all persons constituting the 
sample are examined for splenomegaly, 
and parasites are sought in blood smears 
taken from each of them, it is possible to 
calculate readily the crude spleen and 
parasite indices for the entire group as 
just described. Of course, a parasite index 
cannot be directly computed from the para¬ 
site incidence observed only in those with 
splenomegaly. Each index should be com¬ 
puted from its own data. In addition to 
the crude index for the entire population 
it is desirable to compute indices for dif¬ 
ferent age groups. The percentage of 
children under 10 years of age in whom 
parasites are found has been called the 
1 Whether the P.D.I. spleens' should be regarded 
as significant or grouped with the negatives depends 
on the circumstances. If the incidence of parasites 
among persons with such spleens is significantly 
higher than among those with normal spleens. The 
P.D.I. spleens may in the case of white children be 
regarded as significant. In the case of negroes, 
they are definitely enlarged. 
endemic index by Stephens and Christo¬ 
phers. 
The smaller the proportion of the indi¬ 
viduals in the group or sample examined to 
all persons with the same characteristics of 
age, sex or race in the general population 
of the area surveyed, the greater the likeli¬ 
hood that chance variation might reveal 
considerable difference in the results if 
further samples were examined. On the 
other hand, when all children between cer¬ 
tain age limits are examined at school on 
a certain day, sampling errors are prac¬ 
tically eliminated, as° the group examined 
includes nearly the whole population 
within those limits of age, sex and race. A 
more extended discussion of these questions 
will be found in Boyd (1930a). 
The scope of the malarial problem is the 
first subject of interest. The local geo¬ 
graphic distribution of residences of in¬ 
fected persons should be shown by a spot 
map. A map indicating the extent of 
malaria—whether the incidence observed 
was of epidemic or endemic prevalence— 
should be supplemented with data cover¬ 
ing, among other considerations: the infec¬ 
tion measured by splenomegaly and blood 
positives, by age groups; numbers of the 
splenic group also positive to parasites; 
size and character of spleen; parasites in 
the general population or in the splenic 
negative group; numbers found with dif¬ 
ferent species of the parasite, and gameto- 
cytes present in blood smears. 
The expression endemic prevalence ac¬ 
knowledges the perennial prevalence of 
malaria with some degree of possible fluc¬ 
tuation, depending upon whether the en¬ 
demic level is normally low, medium, high 
or even greater. The limits of annual 
fluctuation are greatest under conditions 
of low endemicity and limited season and 
diminish as the level of endemicity in¬ 
creases. Malaria may attain epidemic 
prevalence after its introduction into areas 
from which it has been previously absent 
or from which it has spontaneously disap¬ 
peared, and after such an introduction 
remain endemically established for an in¬ 
definite period. Furthermore, the wider 
