PROBLEMS IN AIR TRAFFIC MANAGEMENT VI-TRITES

management: IV. Comparison of pre-employment, job-
related experience with aptitude tests as predictors of
training and job air traffic control spe-

performance of
cialists. Aerospace Med. 35:428, 1964.
14. Tas. > Ky: Ground support personnel. Aeroepace Med.,

6. Tame | » and Cops, B. B.: CARI research on air
traffic control specialists: Age, aptitude, and experience

1194 Aerospace Medicine » December 1964

as predictors of performance. Unnumbered Report, Civil
Aeromedical Research Institute, FAA, Oklahoma City,


PROBLEMS IN AIR TRAFFIC MANAGEMENT VI-TRITES

The descriptions of the factor areas, tests, and the
predicted relationships with age are contained in
Table I.

A number of the Civil Service Commission (CSC)
tests described in Table I, are alternate forms of the
tests now being used to select all new ATCS trainees.
The specific tests used for actual selection are those
which enter into the CSC Composite score (Variable
38 in Table 1). These were chosen for an operational
battery after intensive evaluation of their usefulness
and represented a culmination of the research whose
initial stages have been described by Cobb.’:? Ac-
counts of the later research published, to date, appear
in a report’® prepared for internal distribution within
the Federal Aviation Agency and in a technical version
of the same material published by the Western Euro-
pean Association for Aviation Psychology.!*

The Composite Score for Commercial Aptitude Tests
(Variable 37 in Table I) was initially developed for
Enroute trainees in the early phases of our research
program.! The remaining three CTMM composite
scores were computed according to directions given
in the Manual for the CTMM tests and can be con-
sidered as estimates of “intelligence” in the non-lan-
guage and language areas as well as an overall estimate
of “general intelligence.”

Personality Scales:—The personality characteriestics
of the ATCS trainees were assessed by the California
Psychological Inventory. This inventory was used be-
cause its 18 scales purported to measure a number of
aspects of personality which were favorable and posi-
tive instead of morbid and pathological. No predictions
were made for the relationships between the CPI
scales and age. Descriptions of the scales are contained
in Table II.

jamples:—Three different types of Air Traffic Con-
trol Specialists are trained by the FAA. The first of
these, the Términal, or Tower, Controller operates at
airports and is concerned primarily with the safe ar-
rival and departure of aircraft from terminal areas. The
second type of specialist is found in the Air Route
Traffic Control Centers scattered throughout the coun-
try. They are referred to as Enroute Controllers and
their principal task is to insure the safe transit of air-
craft between terminal areas. The final type is the
Flight Service Specialist (FSS) .who acts as a com-
munications link for all aircraft.

Since the training programs for the three ATCS
types differ and because of known differences in demo-
graphic characteristics of those entering each kind of
training, most of our previous research has treated
each speciality as a separate group. In the present
study, however, no information about job separation or
retention was available for FSS trainees. Consequently,
none were included in the analyses. Job separation
and retention data were available for large numbers
of Terminal and Enroute trainees, but the relatively
small number of those separating from the FAA re-
quired that these two types of trainees be pooled in
order to have a sufficiently large number of cases in
the Pass-Separated group.

Also, the tests and scales described in Tables I and
II were not administered to all ATCS trainees. Table

III contains a listing of the time periods during which
each test was administered and the number of cases
in each group who took the test, or scale.

Definitions of Criterion Groups and Age:—The three
trainee criterion groups mentioned previously were
defined in the following manner: (1) Fail: Trainees
failing to complete an 8 week ATCS training course at
the FAA Academy for reasons pertaining to unsatis-
factory performance in the academic or laboratory por-
tions of the course. Those who withdrew from training
for reasons beyond their control, such as illness or
family problems, were not considered as failures and
were eliminated from all analyses. This group was
predicted to have the lowest means on the aptitude
variables and, on the average to be the oldest group.
(2) Pass-Separated: Trainees completing their basic
ATCS training course at the FAA Academy and suc-
cessfully passing the final Air Traffic Control Specialist
Certification Examination at the end of the course, but
who subsequently left the FAA prior to completion of
approximately one year of employment. This group
was predicted to have intermediate means on the apti-
tude variables and be intermediate in mean age. (3)
Pass-Retained: Trainees similar in training accomplish-
ments to the Pass-Separated group and who were still
employed by the FAA approximately 10 months after
completion of FAA Academy training. This group was
predicted to have the highest means on the aptitude

1081
ass-neTai

wh

Fig, 1. Aye distributions of ATCS trainee criterion groups
entering training for the period September, 1960, through June,
1962 (Total N = 1353).

Aerospace Medicine + December 1964 1185



PROBLEMS IN AIR TRAFFIC MANAGEMENT VI—TRITES

soning test of the Mechanical Knowledge Factor, and
between age and the CSC Verbal Analogies test. (In-
duction Factor), the CTMM Verbal Comprehension
test of the Verbal Comprehension Factor, and the total
CTMM- Language Composite score. It would seem
then, that the intuitive expectation of a positive rela-
tionship between age and Verbal Comprehension has
been supported,

Even though the remainder of the variables did not
have statistically significant correlations with age, a
survey of the algebraic signs of their correlations is of
interest. Generally, those tests involving the solution of
new types of problems or reasoning (Induction Fac-
tor) were negatively related to age; whereas those
tests involving verbal aptitude (Verbal Comprehen-
sion Factor), numerical aptitude (Number Facility
Factor), or other knowledge (Mechanical Knowledge
Factor) were positively related to age. Since we are
dealing here with statistically insignificant relation-
ships, exceptions to these general trends are to be
expected; but overall the findings do seem to be in
agreement with the results involving the statistically
significant correlations.

‘With respect to the interactions of age, test per-
formance, and the criterion groups, the mean test per-
formance of the criterion groups differed significantly
on all but 3 of the 36: variables having homogeneous
regressions, irrespective of the age differences between
groups. In all 33 comparisons, the Fail group had the
‘lowest mean score.

Of course, in those covariance analyses involving
aptitude variables having a positive relationship with
age, the unadjusted mean score for Fails was higher

aot (ouApIUSTED MEANS »——

rem wenn

nosusreo Fe 7.29 R«.000)

seb \

(en (ty lve
CRITERION GROUPS
Fig. 2. Unadjusted and adjusted (for age) mean scores of the
three ATCS criterion groups on the CTMM verbal concepts
(vocabulary) test.

1190 Aerospace Medicine + December 1964

than the adjusted mean, The converse was true for
variables having a negative correlation with age. But
for only two variables did the regression adjustment
lead to pronounced changes in statistical significance
or interpretation. These two are illustrated in Figures
2and 3.

In Figure 2, the unadjusted and adjusted mean
scores on the CTMM Verbal Concepts (Vocabulary)
test are plotted for each of the three criterion groups.
Since there was a positive correlation of 33 between
the test score and age, the covariance adjustment pro-
duced a relatively large shift in the means. The rela-
tionship between the test and criterion groups was
changed from a statistically insignificant one to a statis-
tically significant difference having the predicted pattern
of Fails with the lowest mean score, the Pass-Retained
with the highest mean score, and the Pass-Separated
mean score in between the other two.

Figure 3 contains a similar plot of unadjusted and

a

[UNADSUSTED MEANS,

‘ADIUSTED MEANS =.

STANDARO SCORE

fas eon
[UMADIUSTED F217 («051
a0 ADlUSTED F = Lor)

On F
ney one

CRITERION GROUPS

Fig. 3. Unadjusted and adjusted (for age) mean scores of the
three ATCS criterion groups on the CTMM similarities test.

oo

adjusted means for the CTMM Similarities test. Origi-
nally the overall difference between the mean test
scores was statistically significant but the correction for
a negative correlation of —.15 reduced the mean differ-
ences to insignificance.

Examination of the differences between the adjusted
mean test scores of the Pass-Retained and Pass-Sepa-
rated groups revealed that on only two tests did the
groups differ significantly, with the Pass-Separated
group having the smaller mean in each case. These two
tests were Air Traffic Problems: Parts I and II and the
RPM Number Facility test. Both of these involve high-
ly speeded tasks with the former negatively related to
age and the latter positively related to age. A third


PROBLEMS IN AIR TRAFFIC MANAGEMENT VI-—TRITES

Speed of Closure: “The ability to unify an apparently disparate perceptual field. into a
single percept.” : -
29. RPM Four-Letter Words: Detect common four-letter words imbedded in
lines of letters. This highly speeded test has a high loading on a possible
factor called “Verbal Closure.” _ ciel
Unknown or Complex Factor Structure
30. Air Traffic Problems, Part. I: Determine whether aircraft may be per-
mitted to change altitude without violating a specified time-separation
rule. Unpublished factor analyses indicate high loadings on the Number

Facility Factor and Induction Factor. ? _
31. Air Traffic Problems, Parts I and II: Twice as long as Air Traffic Prob-
tems, Part I. ? =

32. RPM Aiming: Ability to carry out quickly and precisely a series of
movements requiring eye-hand coordination. — _
33. CSC Oral Directions: From orally presented information, decisions must

be made regarding performance of simple tasks. ? +
34. CTMM Language Composite: A sum of Variables 12, 15, 23, and 25. ? +"
35. CTMM Non-Language Composite: A sum of Variables 2, 3, 4, 5, 6,
20, 21, and 22, = a
36. CTMM Language plus Non-Language Composite: An overall estimate of
“«general intelligence” composed of Variables 33 and 34. ? +
37. Composite Score for Commercial Aptitude Tests: A sum of Variables
1, 2, 11, 18 and 30, weighted 14, 49, 13, 6, and 18, respectively. ? =
Composite Score for CSC Aptitude Tests: A sum of Variables 7, 9, 14,
19, 31, and 33 each weighted 2, 2, 1, 2, 1, 1, respectively. ? -

1 Factor descriptions are quotations from: French, J. W., Ekstrom, Ruth B., & Leighton, A. P.

Manual for kit of reference tests for cognitive factors. Educational Testing Service, 1963. Princeton, N. J.

Test Names preceded by DAT were part of the Differential Aptitude Test Battery, Form A, 1947, published
by the Prychological Corporation, New York, N. ¥.; those preceded by CTMM were part of California
‘Test of Mental Maturity, Advanced, Form A, 1957, published by the California Test Bureau, Los Angeles,
California; those preceded by RPM are part of a battery of Repetitive Psychometric Measures developed
by Dr. L. J. Moran and published for experimental use in 1959, by the Hogg Foundation for Montal Health,
‘The University of Texas, Austin, Texas; those preceded by CSC are issued by the United States Civil
Service Commission; and the Air Traffic Problems tests were originally developed by the American Institute
for Research, Pittsburgh, Pa., under contract with the Civil Aeronautics Administration in 1950, Forms
‘used in the present research were extensive revisions of the originals tests and were prepared by the Selec-
tion Section, Psychology Laboratory, Civil Aeromedical Research Institute, Oklahoma City, Oklahoma,
* Relationship significant at less than the .05 level.

‘** Relationship significant at less than the .01 level.

+ Regression lines were significantly heterogenous for these tests.

variables, and, on the average, be the youngest group. rated were obtained, approximately 10 months after

Information used to classify an individual as a Fail completion of FAA Academy training, from the field
was supplied by the FAA Academy. Data used to facility to which the individual had been assigned. For
classify an individual as Pass-Retained or Pass-Sepa- a few individuals, the: retention-separation data could

TABLE II. DESCRIPTION OF PERSONALITY SCALES?

Scale Name Description

1, Dominance ‘To assess factors of leadership ability, dominance, persistence, and social initiative.

2. Capacity for status ‘To serve as an index of an individual’s capacity for status (not his actual or achieved status). The scale
attempts to measure the personal qualities and attributes which underlie and lead to status.

3. Sociability To identify persons'of outgoing, sociable, participative temperament.

4. Social presence To assess factors such as poise, spontaneity, and self-confidence in personal and social interaction.

5. Self-acceptance To assess factors such as sense of personal worth, self-acceptance, and capacity for independent thinking and
action.

6. Sense of well-being To identify persons who minimize their worries and complaints, and who are relatively free from self-doubt and
disillusionment.

7. Responsibility To identify persons of conscientious, responsible and dependable disposition and temperament.

8. Socialization To indicate the degree of social maturity, integrity, and rectitude which the individual has attained.

9. Self-control To assess the degree and adequacy of self-regulation and self-control and freedom from impulsivity and self-
centeredness.

10, Tolerance ‘To identify persons with permissive, accepting, and non-judgmental social beliefs and attitude.

11, Good impression ‘To identify persons capable of creating a favorable impression, and who are concertied about how others react
to them.

12, Communality To indicate the degrée to which an individual’s reactions and responses correspond to the modal (‘‘common”)
pattern established for the inventory.

13. Achievement via conformance To identify those factors of interest and motivation which facilitate achievement in any setting where con-
formance is a positive behavior. °

14, Achievement via independence ‘To identify those factors of interest and motivation which facilitate achievement in any setting where autonomy

and independence are positive behaviors.

15, Intellectual efficiency To indicate the degree of personal and intellectual efficiency which the individual has attained.

16, Psychological-mindedness ‘To measure the degree to which the individual ‘is interested in, and responsive to, the inner needs, motives,
and experiences of others.

17. Flexibility To indicate the degree of flexibility and adaptability ofa person’s thinking and social behavior.

18. Femininity To assess the masculinity or femininity of interest. (High scores indicate more feminine interest, low scores

more masculine.)

1 Descriptions of the scales are quoted from the Manual prepared by Dr. H. G. Gough for the California Psychological Inventory and published by Con-
suliing Psychologist Press, 1960, Palo Alto, Cal.

Aerospace Medicine * December 1964 1187



PROBLEMS IN AIR TRAFFIC MANAGEMENT VI-TRITES
TABLE I—DESCRIPTION OF COGNITIVE FACTORS AND APTITUDE TESTS

‘Relationship
with Age

Cognitive Factor and Test* “Predicted Obtained

Induction: “Associated abilities involved in the finding of general concepts that will
fit sets of data, the forming and trying out of hypotheses.” -
1. DAT Abstract Reasoning: Indicate which of a series of choices (figures)
properly carries out of a principle of logical development exhibited by a
sequence of figures: - ~
CTMM Analogies: Seven’ drawings’ of different objects are presented for
each item. The first object has a definite relationship to the second which
must be recognized in order to identify, by analogy, the drawing among
the last four which is similarly related to the third drawing. - _"
3., CTMM Opposites: Select from among several alternatives a pictured
‘object which is most opposite to a stimulus object in terms of its nature,
position, of iaéaning. - ~-
4. CTMM Similarities: Seven drawings of different objects are presented for
‘each item. Select from the last four drawings one. which is similar to
the first three. . . - —
5. CTMM Number Series: Indicate which of a series of numbers properly

‘carries out a principle of logical development. exhibited by a sequence

of numbers. = ~
. 6 CTMM Coins: Manipulate mentally interrelated amounts of money and

namber of coins. - -

7. CSC Abstract Reasoning: Similar to DAT Abstract Reasoning.
8 CSC Number Series: Similar to CTMM Number Series, .
9% CSC Letter Sequence: Similar ‘to Number Series tests but using letters. = — -
10. CSC Verbal Analogies: Seven words are presented for-‘cach’ item. Select

from the last five words one which is related to the third word in the

I
i

_ same way that the first two words are related. . ? +
i Number Facility: “The ability to manipulate numbers in arithmetical operstions rapidly." —
: 11, DAT Numerical Ability: Test of arithmetic computational skill: ? +
12, CTMM Arithmetic: Word, problems must be solved involving simple
arithmetic and mathematical situations. ? +
13, RPM Number Facility: Highly speeded test of ability to.add one or two-
digit numbers’ in sets ot three. +"

14, CSC Computations: Test of arithmetic computational skill.
Verbat Comprebention: “The ability to understand the English language.”
18. CTMM Verbal Concepts (Vocabulary): Multiple choice vocabulary: ‘est.
16. DAT Language Usage-Sentences: Indicate all parts of sentences containing
errors in grammar, punctuation, or spelling.
17. CSC Sentence Arrangement: Rearrange lengthy sentence to form a proper

+

narrative. +
Visualization: “The ability to manipulate or transform the image of spatial patterns
: into other visual arrangements.” ?
i 18. DAT Space Relations: Identify solid figures that can be made from an
unfolded pattern. ? —"
19. CSC Spatial Patterns: Identify solid figures that can be made from an
unfolded pattern or, from various views of an object, identify the object
in a series of alternatives. ? -
Spaiit Oriensetion: “The ability to perceive spatial patterns or to maintain orientation
with respect to objects in space.” ?
“CTMM Sensing Right and Left: Discriminate between right and left for
Pictured objects auch as vatious parts of the human anatomy, clothing,
? +
21. CTMM Manipulation of Areas: Identify three dimensional spatial drawings
representing different views of a stimulus object. ? -
Associative (Rote) Memory: “The ability to re bits of unrelated material.” —

22. CTMM Immediate Recall: Series of words are pronounced in pairs: After
each series, the first word of each pair is pronounced again, and the
word that went with it must be recalled from among three objects
pictured in each item. =

+1

23, CTMM Delayed Recall: Recall facts of a story after an intervening period, — —
Mechanical Knowledge: “Knowledge of mechanical principles, devices, and tools, acquired
through experience and training.” ?
2%. DAT Mechanical Restoning: Through « study of drawings depict the
‘operation of physical and mechanical principles determine the correct
ftatement describing & situational outcome feotiting from application of
ciple, ? “
Syhogistic Rewoning “Ability to reason from stated premises and derive logical con-
clusions. z
28, CTMM Inference: Comprehend statements presenting premises and derive
logical conclusions. ? -
Perceptual Speed: “Speed in finding figures, making comparisons, and carrying out other
very simple tasks involving visual perception."” =
26, RPM Perceptual Speed: Detect and cross out all numbers ini a row that
are like a circled number at the beginning of each row. Highly speeded. = — -
Spatial Scanning: “Speed in visually exploring a wide or complicated spatial field.” -
27. RPM Visualization: Follow visually the path of lines in a tangled pattern
of such lines. Highly speeded, . oe
Plasibility of Closure: “The ability to keep one or more definite configurations in mind
0 as to make identification in spite of perceptual distractions.” —, -
28. RPM Copying: Copy four-line geometrical figures onto a ‘matrix of dots.
Highly speeded. - 4

1186 Aerospace Medicine * December 1964



PROBLEMS IN AIR TRAFFIC MANAGEMENT VI-TRITES

TABLE V. CORRELATIONS (r) WITH AGE, ADJUSTED AND UNADJUSTED CRITERION GROUP MEANS (X),
‘AND F-TEST VALUES FOR ALL APTITUDE TEST VARIABLES

‘Unadjusted Means ‘Adjusted Means
Factor and Pass Ret. Pass-Sep. Fal Pasi-Ret. Pass Sep, Fail
Test r x N x N x N F x xX x FE
Induction
DAT Abst. Reas. 36.0 6264792 294 186 «17.6 tt = 35.7348 SOR. TT
CTMM Analogies 7.0 626 67 9S 62 18717 tt 70 67 63774
CTMM Opposites 76 (458 74 69 «1365 76. «75 70 38%
CTMM Sirnilar 102 458 = 10.3, 82 97 1360 3.2" 102 10300 99
CTMM Number Series 6.2 © 458 6.0 = 82 SA 136121 tt 6.2 6.0 5.2 8.6 tt
CTMM Coins 85 458 85 82 67 136 20.3 tt a4 8S 6B GSH
CSC Abstract Reas, 12703473433 105 16094 tt =| 126 13.5108 7.5 Ht
CSC Number Series 25 M47 24 33 17 160 (10.7 tt a4 24 BTA
CSC Letter Sequence 11434710833 73 160 422th | 13 1047.8 ATT
CSC Verbal Analogies 105 4700 O33 93 160 «© BT TT = 10610. 10.8 TE
Number Facility .
DAT Number Ability 04 23.6 © 626 22.993 182 1858.8 tt 238228178106 tt
CTMM Arithmetic 08 * 86 458 89° 82 7A 1360143 Ht a7 89 7.3 (16.3 tt
RPM Number Facility U0* 384 6233883 347 «186A TY 8G BSLT AL 1S. TE
‘CSC Computations 06 7) 4740S 3338.0 1609 0.437.714. HT
Verbal Comprehension
‘CTMM Verbal Concepts ae 24 458 LBL 20.6 136 9 18 260 19.2 7.3 tt
DAT Lang. Usage-Sent. gt 3720 «4588279 413528 377-380 33.0 At
CSC Sent. Arrangement 05 37047 40 © 33 33 1604.8 3700390 325A
Visualization
DAT Space Relations 63.0 6498 S10 185 SLOTt = 62.6 63.3 S20, 23.0 tT
CSC Spatial Patterns m7 7 BH 3B 24160288 tt 27.6 8718 HT
Spatial: Orientation
CTMM Sensing R & L O1 1720488178 16213698 Tt | 172A 162 OBIT
CTMM Manip. of Areas —07 81 458 84 82 72 1367.6 tt B10 8474 5.6 TF
Associative (Rote) Memory .
CTMM Immed. Recall —a 304 458 30.3 BE 28.7 136 0.2tt «= 30.8. 30,3 288A. HT
CTMM Delayed Recall 05 1720 4587.3, 81 189 1364 TE 7273189 ASA TE
Mechanical Knowledge “
DAT Mech. Reasoning 26% 43.7. 4B AGS 79 ALT 13ST 443 46.0 39.9 8.6 TE
Syllogistic Reasoning
CTMM Inference 08 120-458 AZA «82 Ma 1361S. = 120 ad Tt
Perceptual Speed
RPM Perceptual Speed 08 * 918 623 8B 8B BH O15 886906
Spatial Scanning
RPM Visualization 0st 343 6233238 310-186 18.4 M2324 BLD KAT.
Flexibility of Closure
RPM Copying 04 10.0 623 97 98 83 1860106 tt = 0.07 A
‘Speed of Closure
RPM 4-Letter Words am 20.6 © 623, 20.5 93 19.1 186 43% 208 203 184 9.6 tt
Unknown or Complex
Structure
‘Air Traf, Prob.: Pt I —07* 157626 13.393 200 186 79th SSA
‘Air Traf. Prob.: Pts. 1 & IT —.08 35103470733 283 160 9.9tt «= 34.9 30.9 28.8 20.5 tt
RPM Aiming —06 108. «622,04. 9S 106, 18H 2.9 108. 104.106. 19
CSC Oral Directions 01 a4 473 169 1607.9 tt = 1 RO 16.9 18.9 FT
CTMM Lang. Compos. (26% 95.1 458948 BL 55.0 1360 Ott | 59.7 89.9 S35 19S Tt
CTMM Non-Lang. Comp,  —14** 95.1 458948 I 868 136 SKS tt | 948 94.9 87.6 HT HE
CTMM Lang. + Non-Lang. 07 15458135, 114,136 TE ISS. 155.41, 28.9 TE
Commercial Test Compos,  —.06 178, «6281738, 934K (NBG SGOT 178,178,147. ST TT
CSC Test Compos. 06 zo, 347,198,337, = 6058.7 HF 201.198.1681 TT

+ Regression lines were significantly heterogeneous for these tests.
* Significant at the .05 level.

** Significant at the .01 level.

tt Significant at the .001 level.

relationships with age, statistically significant negative
correlations were obtained between age and test
scores in 3 of the factor areas, These were: (1) The
Induction Factor as measured by the DAT Abstract
Reasoning test and the CTMM tests of Analogies Sim-
ilarities, and Number Series; (2) the Associative Mem-
ory Factor measured by the CTMM Immediate Recall
test; and (3)-one highly speeded test representing the
Perceptual Speed Factor. Among the 4 remaining fac-
tor areas with negative predictions, a negative correla-
tion was obtained for the RPM Visualization test
representing the Spatial Scanning Factor. Unfortunate-
ly, the regression lines for the three subgroups were
heterogeneous which makes interpretation of the age-
Visualization test correlation difficult. RPM Copying,

a highly speeded test assigned to the Flexibility of
Closure Factor, had an insignificant positive correlation
with age; and the RPM Four-Letter Words test
(Speed of Closure Factor) had a significant positive
correlation with age as did two (CTMM Arithmetic
and RPM Number Facility) of the four tests assigned
to the Number Facility Factor.

Three additional negative and significant correla-
tions between age and test scores were obtained. The
first with the total CTMM Non-Language Composite
score was predicted. The other two were with the DAT
Space Relations, test measuring the Visualization Fac-
tor and the test of Air Traffic Problems, Part I.

Statistically significant positive correlations were also
obtained between age and the DAT Mechanical Rea-

Aerospace Medicine » December 1964 1189



AM 65-21

PROBLEMS IN AIR TRAFFIC MANAGEMENT:

VI. Interaction of Training-Entry Age With Intellectual and
Personality Characteristics of Air Traffic Control Specialists

David K. Trites, Ph.D.

Approved by Released by
Srantey R. Mouter, M.D. M.S. Wurre, M.D.
Dmecror, CARI Feprrat Air Sureron
July 1965

FEDERAL AVIATION AGENCY

Office of Aviation Medicine
Civil Aeromedical Research Institute
Oklahoma City, Oklahoma



PROBLEMS IN AIR TRAFFIC MANAGEMENT VI-TRITES

DISCUSSION

As in other studies of samples from different popula-
tions, the comparison in the present investigation of
older versus younger people indicated that older indi-
viduals had greater aptitude test decrements in meas-
ures of nonverbal reasoning and the solution of novel
tasks, immediate memory for new material of an un-
usual nature, spatial relations, and certain highly
speeded tasks.*-° On the other hand, older individuals
had greater aptitude test increments in measures of
verbal comprehension, numerical operations, and me-
chanical knowledge. In addition, certain highly speed-
ed tasks were unexpectedly found. to be positively
correlated with age.

The different relationships between age and highly
speeded tests emphasize the need to take test content
into account. For example, two highly speeded tests
positively related to age involved, in the one case,
simple numerical operations (a measure of the Num-
ber Facility Factor) and, in the other, identification of
common four-letter words (Speed of Closure Factor).
This latter test has been shown by several of our un-
published factor analyses to have a high loading on a
factor similar to the Verbal Comprehension Factor sug-
gesting that it may be more highly related to a verbal
ability than to the Speed of Closure Factor which it
was initially thought to measure. Within the frame-
work of this study, then, the expected negative rela-
tionships between age and speeded tests were nullified
by test content in some instances.

The positive correlations between age and numerical
operations are in agreement with the findings of Glan-
zer, Glaser, and Richlin who, in their study of rated
officers of the Air National Guard and commercial
airline pilots, reported a positive correlation of .08
(P<.10) between a test of numerical operations and
age.° A contradiction between their study and this one
occurred in the area of mechanical reasoning or me-
chanical principles. They found a significant negative
correlation of —.12 (P<.01), and we found a signifi-
cant positive correlation of .26 (P<.01). Accounting
for this discrepancy, be it caused by differences in the
tests used to measure the factor or in the characteristics
of the samples, certainly calls for additional research
since logically one can defend the expectancy of either
a positive or negative relationship.

Overall, Failures in ATCS training proved to be an
inferior group in terms of the aptitudes assessed when
compared with trainees who either passed the training
and were retained with the FAA or who passed and
were separated from the FAA. The results suggest
that the higher training failure rate of older individuals
may be partially accounted for by age-related deficien-
cies in non-verbal abstract reasoning, immediate mem-
ory for new and different material, and by the require-
ments to perform their job tasks-rapidly and accurately.
Since the Air Traffic Control Specialist must have
a good memory, constantly assimilate new information,
think in abstract terms: and work rapidly, it is not
surprising that older individuals coming into the occu-
pation have difficulty adjusting to its demands. This is
counterbalanced to some extent by the superior ability

1192 Aerospace Medicine * December 1964

of older individuals to handle arithmetic computations
more correctly and their superior verbal comprehen-
sion as compared to younger trainees, but this is not
sufficient to offset their deficiencies.

With respect to job performance as reflected by re-
tention or separation from the FAA within the first
year after completing ATCS training, those who sepa-
rate appear to be deficient primarily in their ability to
perform arithmetic operations rapidly and correctly
and, to a lesser degree, in non-verbal abstract reason-
ing. This was indicated by the fact that the two tests,
on: which performances of the Pass-Retained group
were significantly higher than the Pass-Separated
group, were a highly speeded test of numerical opera-
tions and a highly speeded test designed especially for
assessment of aptitude for air traffic control work. Un-
published factor analyses of this latter test revealed
that it is highly related to non-verbal abstract reason-
ing and number facility.

As pointed out previously, the patterning of the
mean differences between the Pass-Retained and Pass-
Separated groups, even though statistically insignifi-
cant, is of some interest. In most cases, the Pass-Re-
tained growp had higher mean scores on tests of
nonverbal abstract reasoning or number facility, and on
highly speeded tasks; whereas the Pass-Separated
group had higher mean scores on tests involving spatial
orientation, spatial visualization or verbal aptitude.

All in all, the findings in this study give continued
support to the appropriateness of the Civil Service
Commission Test Battery currently being used to se-
lect all new ATCS trainees, insofar as prediction of
training failure is concerned. With respect to the dis-
crimination of those who pass and are retained from
those who pass and are separated early, the evidence
is not as clear. Although the CSC Composite score does
discriminate as expected between the Pass-Retained
and Pass-Separated individuals, on 3 of the 6 tests
(CSC Abstract Reasoning, CSC Spatial Patterns, and
CSC Oral Directions) forming the composite score,
the Pass-Separated group had a higher mean score
than the Pass-Retained group. The differences were
not statistically significant but do contribute to the
reduction in the difference between means of the Pass-
Retained. and Pass-Separated groups on the CSC Com-
posite score.

It is tempting to conclude that only the three CSC
tests on which the Pass-Retained individuals have
higher mean scores than the Pass-Separated (CSC

» Computations, CSC Letter Sequence: and Air Traffic

Problems, Parts I and II) should be used in the selec-
tion process. This is particularly true in light of the
finding that the only tests significantly discriminating
these two groups were the air traffic problems test
and one of the numerical ability tests. However, this
conclusion is not warranted until further research has
demonstrated whether the current findings are mere-
ly a matter of random variation in the samples of
trainees used, what loss in efficiency of prediction of
training failures might occur as a result of deletion of
the three CSC tests, and what differences in test per-
formance characterize the three different types of
ATCS trainees,


PROBLEMS IN AIR TRAFFIC MANAGEMENT VI-TRITES

test, RPM Visualization measuring the Spatial Scan-
ning Factor, also had a significant difference between
the mean scores of the Pass-Retained and Pass-Sepa-
rated groups’ but, as mentioned previously, the hetero-
geniety of the group regressions for that test clouded
interpretation of the statistical test of significance.

The remainder of the variables revealed an intri-
guing pattern of mean differences between the two Pass
groups. Mean scores for the majority of spatial tests
and tests involving language were higher for the Pass-
Separated group. In this context, the tests measuring
the Visualization Factor form a logical cluster with
the DAT Mechanical Reasoning test since, as pointed
out by French, Ekstrom, and Price, “Visualization is
important to Mechanical Movement and Mechanical
Comprehension tests . . .”° On the other hand, the
mean scores for the majority of numerical and induc-
tion tests were higher for the Pass-Retained group.

These opposed trends obviously accounted to some
extent for the lack of significance between means of the
Pass-Retained and Pass-Separated groups on the Com-
mercial Composite score and the CSC Composite score.
It should be noted, however, that in spite of all the
counteracting trends influencing these two composites,
the Pass-Retained. group still had the highest adjusted
mean score on eas

The other three composite scores, CTMM Language,
CTMM Non-Language, and the sum of the two, had
relationships with age and the criterion groups which
were logical’ knowing the relationships between age.
and the individual components of each composite.
The Language score was positively correlated with
age (.26, P<.01), the Non-Language score was nega-
tively correlated (—.14, P<.01), and the sum of the
two was positively, but insignificantly, correlated with
age. For all three composites the adjusted mean scores
of the Fails were significantly lower than the Pass

groups with the largest relative difference (by stand-
ard score conversions) occurring in the Non-Language
area prior to correction of the means for the age effect.

Personality Variables:—Table VI contains the criterion
group means of the 18 scales of the California Psycho-
logical Inventory (CPI) unadjusted and adjusted for
their regression on age, the correlations between the
scales and age: and the F-test values. Eleven of the 18
scales had significant positive correlations with age,
the largest of which was only .17. For the remaining
7 scales, all but 1 had insignificant negative correlations
with age.

From this, it may be concluded that the older train-
ees reported themselves as being more intellectually
efficient, dependable, interested in leadership and
dominance, oriented toward achievement in situations
where either conformance or independence are posi-
tive behaviors, self-controlled, tolerant and understand-
ing of others, socially oriented, and not preoccupied
with worries and self-doubt. In spite of these positive
relationships, the statistical tests for the adjusted mean
differences revealed that Fails were actually less in-
tellectually efficient, less oriented to achievement in
situations where either conformance or independence
are positive behaviors, less tolerant of others, Jess in-
terested in leadership and dominance, less dependable,
and more preoccupied with worries and self-doubt
than. were the Pass-Retained and Pass-Separated indi-
viduals. In addition, it was found that among the Fails
the adjusted mean of their self reports of social matur-
ity, integrity and rectitude, and the agreement of their
responses with the common pattern established for the
CPI were significantly lower than means of the two
Pass groups. In none of the comparisons of adjusted
mean scores were the Pass groups found to differ sig-
nificantly.

TABLE VI. CORRELATIONS (r) WITH AGE, ADJUSTED AND UNADJUSTED CRITERION GROUP MEANS (X),
‘AND F-TEST VALUES FOR THE PERSONALITY SCALES

‘Unadjusted Means

Adjusted Means

Pass Ret. Pass-Sep. Fal PaseRet. Pass-Sep._ Fail

CPI Scale =x N x N x N F x x x F
1. Dominance rc nr 7 eS eS co) 28 291 276 33°
2. Capacity for Status pe 196622979319, a 19.7 19.6 19.2, 1
3. Sociability 108 * 235 6228.7 9S ST BS a 25.6 25.7 25.4 a
4. Social Presence 01 o2 5393S BS 359 35.3 38.2 a7
5, Self-acceptance —03 oA 9418S eT m2 2 LD 0
6, Sense of Well-being tows 389 22 BS MH B.Z BS 39.0 384 38.0 ait
7. Responsibility ‘ye 3080 22sl—(atit HBS SMF 80.9 B10 29-2 10.6 F
8. 'Sécialization 01 ya ats 7 H8518S SBM BTL 85.6 3.240
9.. Self-control “oe 30.7622 SL 94 SL 85 3 309 310 30.7 a
10, Tolerance ‘ise 220 6221 HBSS 221 - 22.0 24.0 a4
11. “Good Impression 08 197 622, «20.1 9S 20. BE 7 198 20.1 20.2 3
12, Communality —02 262 © «622,—=:«—«6 SG « BE GOH 2G 26.0 5.6 age
13. Achigvernent via .

Conformance ast 6623284 938.0 BHO 28.7 837 3a
14; Achievemént via

Independence ag 178 os. dN 7.8 180168 sae
15, Intellectual

Efficiency 08 * 3602289 HC 87S BS SH BT BB 37.0 rat

16; Psychological-

miindedness age* 1S 6229S 8S 9 M60 16M 29
17, Flexibility 04 82 622 a2 (98 79185 3 8.2 82 8.0 a
18. Femininity 05 16.2 622, 16.1 9516.4 185 4 16.2 16.1 16.5 2

* Significant at the .05 level.
+ Significant at the 01 level.
+ Significant at the .001 level.



PROBLEMS IN AIR TRAFFIC MANAGEMENT VI-TRITES

TABLE I1I—SAMPLE DESCRIPTIONS AND TESTS ADMINISTERED TO EACH SAMPLE

Number of Cases in

Sample ‘Time Period ‘Tests or Scales Pass-Ret. Pass-Sep. Fail
1 Sept., 1960-July, 1961 From Table 1, Variables Numbered: 3, 4, 5, 6, 12, 15, 16, 20, 21, 458 a2 136
22, 23, 24, 25, 30, 34, 35, 36
2 Sept., 1960-Jan. 1962 ‘From Table 1, Variables Numbered: 1, 2, 11, 13, 18, 26, 27, 28, 626 95 187
29, 32, 37; and all variables in Table 2
3 July, 1961-June, 1962 From Table 1, Variables Numbered: 7, 8, 9, 10, 14, 17, 19, 31,'33, 38 M7 33 160

\ The numberof individuals actually administered any particular test may vary slightly from the N’s given here as a result of missing data.

not be obtained from a facility. Such individuals were
deleted from the study.

The decision to use Retention-Separation after train-
ing as the criterion of job performance rather than
some index involving ratings by an individual’s super-
visors was based upon several considerations. First, the
fact of retention or separation was completely objec-
tive. Second, there can be no doubt that the separation
of an individual within less than a year following com-
pletion of ATCS training represents a distinct mone-
tary loss to the FAA and can be considered presump-
tive evidence of unsatisfactory adjustment to the FAA’s
working environment. Naturally, some separated for
reasons not related to performance or adjustment, such
as health or a better job opportunity, but the. data
furnished by facilities indicated that the vast majority
of those in the Pass-Separated group were considered
deficient in job performance or adjustment. A third
consideration was the. unavailability of supervisory
ratings for many of the separated individuals. Finally,
any ratings which were available for separated in-

1 dividuals had to have been made in retrospect; and it

! is likely that the fact of separation would have given a

i negative halo to such an individual regardless of the
reasons for separation.

Age at entry into training was recorded to the near-
est birthdate, The distribution of ages of trainees was
skewed with the majority of trainees in the 22 to 26
year age range. The distribution. was also definitely bi-
modal with a secondary peak in the 38 to 41 year
range.* Figure 1 contains the frequency polygons for
the three trainee-criterion groups and the total of all
Enroute and Terminal course trainees coming to the

*In a previous study,!1 the age distribution of Enroute
trainees was found to contribute most to the bimodality. Un-
fortunately, several items of information which might have
helped in the interpretation of the age distribution and other
results of the investigation were not available; @.g., the propor-
tion who were retired military personnel and complete work
histories of all trainees.

FAA Academy from September, 1960, through June,
1962,

Statistical Methodology:—The analyses of the inter-
action of training-entry age and the other variables
were bi upon the covariance analysis techniques
described by Snedecor.® As programmed for an IBM
1620 computer, the’ output contained all relevant sta-
tistical information, including a test of the homogeni-
ety of the regressions of the criterion groups and a
within-groups correlation coefficient. This latter statis-
tic was selected as the appropriate estimate of the
correlation between age and the other variables.’ ® To
test the significance of the differences between ad-
justed means .of the Pass-Retained and Pass-Separated
groups on each variable, the adjusted within-groups
variance estimate was used in the conventional formula
for a t-test. As for the assumptions underlying use of
the covariance technique, a survey of the data in-
dicated that all were tenable.

RESULTS

Table IV contains the means and standard deviations
of the age distributions for each group of trainees, In
every case, the differences between the mean ages
were statistically significant in the anticipated direc-.
tion; i.e., the Fails were oldest, the Pass-Retained the
youngest, and the Pass-Separated in between the other
two groups.

Aptitude Variables:—Table.V contains the criterion
group means of all aptitude variables unadjusted and
adjusted for their regression on age, the within-groups’
correlations between the variables and age, and the
F-test values for differences in the unadjisted and
adjusted means. Of the 38 individual and composite
aptitude variables listed in the table, only two were
found to have significantly heterogeneous regressions—
‘DAT Language Usage and RPM Visualization. This
precluded the interpretation of their F-tests. Table I
contains a summary of the signs and statistical’ signifi-
cance of the obtained correlations.

Of the 7 factor areas predicted to have negative

TABLE IV. MEAN AGES OF THE THREE ATCS TRAINEE CRITERION GROUPS AND THE
POOLED MEAN AND STANDARD DEVIATION OF AGE IN EACH SAMPLE?

Pass-Retained Pass-Separated Fail Pooled

Samples x N x N x N x S.D. N
1 27.0 458 28.8 2 316 136 28.1 62 6
2 26.9 626 28.7 95 315 187: 28.1 6.2 908
3 = 26.5 347 29.7 33 31.8 160: 28.2 64 340

1 Within a sample, the differences between the mean ages of the criterion groups are all significant at’ less

than the .001 level.

1188 Aerospace Medicine + December 1964


Problems in Air Traffic Management
VL. Interaction of Training-Entry Age with
Intellectual and Personality Characteristics

of Air Traffic Control Specialists

Davo K. Tarres, Px.D.

‘VIOUS RESEARCH HAS conclusively demon-
strated that a substantial negative relationship ex-
ists between an individual's chronological age at entry
into Air Traffic Control Specialist (ATCS) training
with the Federal Aviation Agency (FAA) and subse-
quent performance in training and on the job. It has
also’ been shown that chronological age at entry into
ATCS training is related to performance on aptitude
tests.2+ 210, 11, 12, 38, 14, 15, 16

The present investigation represents an exploration
of the interaction of training-entry age of Air Traffic
Control Specialists with their intellectual and person-
ality characteristics as assessed by paper-and-pencil
tests at the time of entry into training. Particular em-
phasis has been placed upon the identification of de-
crements in specific aptitudes, or cognitive abilities,
which may predispose the older trainees to less effec-
tive training and job performance.

In order to present a more meaningful description
of the various aptitude tests administered to over 900
Enroute and Terminal ATC trainees, the contents of
the tests were examined and matched with the cogni-
tive factor areas described by French* and French,
Ekstrom and Price.* Although some tests could not be
matched and others were obviously poor measures of
the factor area to which assigned, it was felt that the
results might have more usefulness and meaning for
other investigators if reported in this frame of refer-
ence.

In addition, the literature on aging, as represented,
for example, by Dennis’ survey® and the study of
Glanzer, Glaser, and Richlin,* was utilized to predict
the direction of the relationships expected to obtain
between the cognitive factor areas and age. Predic-
tions could not be made for all factors and, for some,
examination of the tests assigned to the factor areas
suggested that different relationships might occur with-

From the Federal Aviation Agency, Civil Aeromedical Re-
search Institute, Aeronautical Center, Oklahoma City,

Dr. Trites is Chief, Selection Section, Psychology Laboratory.

Opinions or conclusions contained in this report are those of
the author, They are not to be construed as necessarily reflect-
ing the views or the endorsement of the Federal Aviation Agency.
Several of the statistical analyses reported in this paper were,
performed as an integral part of Contract Number FA/AC-4-730
‘between the Civil Aeromedical Research Institute and the Bio-
statistical Unit of the University of Oklahoma Medical Center,
Oklahoma City.

1184 Aerospace Medicine + December 1964

in a factor area as a function of differences in test con-
tent.

Finally, the aptitude and personality differences
serving to distinguish three types of training and job
performance outcomes were studied. To accomplish
this, ATCS trainees were classified as failures in train-
ing (Fail), passing the training course but leaving the
FAA’s employment within one year after train-
ing (Pass-Separated), and passing the training course
and still employed by the FAA (Pass-Retained).

PROCEDURE

Cognitive Factors and Aptitude Tests:-The paper-
and-pencil tests administered to the ATCS trainees
were part of an experimental testing program designed
to improve selection of Air Traffic Control Specialists.
They were administered to the trainees prior to their
entry into training at the FAA Academy, Oklahoma
City, and yielded 33 discrete scores and 5 composite
scores. All but 4 of the 33 individual test scores were as-
signed to 1 of 12 cognitive factor areas.

Negative relationships were predicted to occur be-
tween age and the tests representing 7 of the 12 factor
areas, The factor areas were those measured by highly
speeded tests (Perceptual Speed, Spatial Scanning,
Flexibility of Closure,.and Speed of Closure), the As-
sociative Memory Factor, the Induction, or non-verbal
abstract reasoning, Factor, and the Number Facility
Factor. For the last factor, the negative prediction was
based primarily upon the fact that one test was highly
speeded (RPM Number Facility Test) even though
some studies ® have suggested that a positive relation-
ship would occur. Based upon the content of the tests
entering into the score, the occurrence of a negative
relationship with age was also predicted for the CTMM
Non-Language Composite.

Intuitively, it was felt that measures related to
verbal aptitude might show an increment with age.
Unfortunately, the evidence relating to this is contradic-
tory since some studies have found little, or no, de-
crement with increasing age* but other studies have
found age-related decrements. ‘This permitted no pre-
diction for the verbal area and suggested that where
verbal ability appeared to enter into performance on a
particular test assigned to one of the factors with a
negative prediction, the direction of the relationship
with age would be ambiguous.




Problems in Air Traffic Management
VI. Interaction of Training-Entry Age with
Intellectual and Personality Characteristics

of Air Traffic Control Specialists

Davo K. Trrres, Pu.D.

Reprinted from AEROSPACE MEDICINE
-Vol. 35, No. 12, December, 1964. © Acrospace Medical Association





PROBLEMS IN AIR TRAFFIC MANAGEMENT VI-TRITES

With regard to the latter point, it has recently been
discovered that measurement of verbal abstract reason-
ing ability (the CTMM Inference test of the Syllogistic
Reasoning Factor in Table 1) makes a distinct con-
tribution to prediction of training success of Terminal
ATCS trainees.* Such was not the case in predicting
training success of Enroute ATCS trainees. Since the
present study pooled both types of trainees, it is pos-
sible that some of the findings may reflect compensa-
tory differences among trainee types.

Until the preceding questions regarding the test bat-
tery being used to select ATCS trainees have been
answered, no harm can result from its continued opera-
tional usé, since the value of the component tests for
prediction of training failure has ‘been repeatedly
demonstrated.

In the personality area, the responses of the older
individuals tended to be more positive than responses
of the younger; i.e., more intellectually efficient, toler-
ant, responsible, worrying less, etc. After correcting the
mean personality scores for the age differentials, Fails
were found to respond less positively in almost every
personality dimension than either of the two Pass
groups. No significant differences were found between
these latter two groups.

It must be emphasized, however, that in the person-
ality realm none of the ATCS groups deviated ap-
preciably from the mean scores of the groups used to
establish the inventory’s norms. We can conclude from
this that, on the average, Air Traffic Control Specialist
trainees are essentially normal individuals, insofar as
normality is defined and measured by the personality
inventory used in the investigation, but that relative
to trainees passing the ATCS course, Fails give a more
unfavorable assessment of themselves.

From the present study, a fairly clear picture of the
successful Air Traffic Control Specialist has emerged.
He is one who is relatively young when he enters the
occupation, thinks rapidly, reasons correctly, is adept
with simple arithmetic, and shows no great deviations
from a normal pattern of adjustment.

SUMMARY

By examining the relationships between age at entry
into ATCS training and scores on aptitude and person-
ality tests of over 900 Enroute and Terminal ATCS
trainees, it was found that: (1) Older trainees had
lower test scores than the younger trainees on tests of
immediate memory and non-verbal abstract reasoning.
(2) Older trainees had higher test scores than the
younger trainees on tests of arithmetic and verbal
ability. (3) In highly speeded aptitude tests, the type
of test (e.g., arithmetic, spatial, vocabulary, etc.)
seems to determine whether the older or younger
trainees have the higher scores. (4) In the personality
area, older trainees were found to be more intellectual-
ly efficient, responsible, tolerant, etc., than their young-
er classmates.

When test scores were examined for groups of train-
ees classified as failures in training, passing training
but leaving the FAA within a year, and passing train-
ing and still have the FAA, it was found that: (1) Us-

ually the failure group had the lowest average test
scores, the pass but separated group the next lowest,
and the pass and retained group the highest average
test scores. (2) The pass-separated group was signifi-
cantly poorer than the pass-retained group in the
ability to rapidly and accurately handle arithmetic,
and, to a lesser degree, in non-verbal abstract reason-
ing. (3) With respect to personality, training failures
were less intellectually efficient, tolerant, responsible,
etc., than the other two groups of trainees. No differ-
ences in personality were found between the pass-
separated and pass-retained groups.

From the research it was concluded that: (1) The
higher training failure rate of the older individuals can
be partially accounted for by inferior aptitudes for
non-verbal abstract reasoning, memory for new materi-
al, and by the inability to work as rapidly and accu-
rately as required in training and on the job. (2) The
group of tests presently being used to select ATCS
trainees contains measures of those aptitudes shown to
be related to retention or separation from the FAA, but
further study of the tests is needed. (3) As a group
ATCS trainees seem to present an essentially normal
picture of their personalities.

REFERENCES

1. Coss, B. B.: Problems in air traffic management: II. Pre-
diction of success in air traffic controller school. Aero-
space Med., 33:702, 1962. Also published as: Civil Aero-
medical Research Institute Report 62-2. FAA, Oklahoma
City, Okla., 1962.

2. Cops, B. B.: Problems in air traffic management: V. Identi-
fication and potential of aptitude test measures for selec-
tion of tower air traffic controller trainees. Aerospace
Med. (in press).

3. Dennis, W.: Age and behavior: A survey of the literature.
School of Aerospace Med., USAF, Brooks AFB, Texas,
Proj. No. 21-0202-0005, Rept. No. 1, 1953.

4, Frencu, J. W.: The description of aptitude and achievement
tests in terms of rotated factors. Psychometric Mono-
graph, No. 5; Chicago: University of Chicago Press,
1951.

, J. W., Exsrrom, Ruta B., and Pricz, L. Ax:
Manual for kit of reference tests for cognitive factors.
Princeton, New Jersey: Educational Testing Service, 1963.
6. Granzer, M., Graser, R., and Ricmuy, M.: Development
of a test battery for study of age-related changes in
intellectual and perceptual abilities. School of Aerospace

1.

8. McNeaan, Q.: Psychological Statistics. New York: Wiley;
2nd Edition, 1955.

9. SNEDECoR, G. W.: Statistical Methods, Ames, Iowa: Iowa

State College Press, 5th Edition, 1956,

10. Trrres, D. K.: Problems in air traffic management: I.
Longitudinal prediction of effectiveness of air traffic
controllers. Aerospace Med., 32:1112, 1961. Also pub-
lished as: Civil Aeromedical Research Institute Report
61-1, FAA, Oklahoma City, Oklahoma, 1961. i

11. Trrres, D. K., and Coss, B. B.: Problems in air traffic
management: III. Implications of age for training and
job performance of air traffic controllers. Rept. No. 62-3,
Civil Aeromedical Research Institute, FAA, Oklahoma
City, Okla., 1962.

12. Tries, D. K., and Coss, B. B.: Problems in air traffic
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13, Trrres, D. K., and Cons, B. B.: Problems in air traffic

Aerospace Medicine + December 1964 1193