64 The Rice Institute Pamphlet
The length of his illness and the degree to which it has af-
fected his normal activities, his job, and his financial status
are relevant variables. The effect of the illness on his family
and their attitude toward him and his operation may be
pertinent. Finally, the patient’s conception of his illness and
of the possible consequences of the operation also enter in.
The neurological disorder is not the only factor influencing
his behavior prior to the operation.
(b) Observations of behavior and tests of performance for
one subject must be interpreted cautiously. No measure of
intellectual functioning is perfectly reliable; judgments of
test reliability can only be made for groups of subjects. In
addition, the conditions listed under (a) certainly make it
difficult to conclude that the pre-operative performance re-
flects the typical behavior of the patient.
(c) The operation itself also provides sources of variability
other than tissue removal. It is difficult to determine whether
all tlιe defective tissue has been excised. Even where that
seems to have been accomplished, scarring and subsequent
atrophic changes might occur. Tumor growths have been
found to cause pathological changes at some distance from
their locus because of compression. In addition, it is neces-
sary to realize the possible effects of the operation on blood
supply, chemical changes in the cells, and the like.
(d) The interpretation of the changes in behavior and test
performance after the operation are subject to the same quali-
fications noted under (b). Variability in performance by a
subject on successive testings is expected; this variability can
only be evaluated if the patient population is sufficiently
large for statistical tests of significance. After the operation
the patient is aware that certain portions of his brain have
been removed and his conception of their significance will
undoubtedly influence his behavior. Moreover, his status as