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OCR for page 45
4
THE RELATIONSHIP BETWEEN THE FIVE
VECTORS OF VARIABLES AND TTD
AND ITS COMPONENTS: A COMPARISON OF
ZERO-ORDER CORRELATIONS
This chapter examines the zero-order correlations between a number of
the independent variables used in the model and l-! l) and its component parts.
The analysis discusses why the data are broken down by field and describes zero-
order correlations between select variables in the five vectors in the model-
family background, student attributes, tuition and financial aid, institutional
environment, and market (economic and social) forces and TTD and its
components. It also provides correlations among the several salary and
employment variables themselves and analyzes the amount of variation in 1 TIP
explained by each vector.
The Importance of Disaggregation by Field
- Existing studies either addressed issues related to ~-1L) aggregated over
all fields (Wilson, 1965) or controlled for field differences using a set of dummy
variables (Abed) and Benkin, 1987~. The former approach ignores the possibility
that a given independent variable (e.g., whether the student has an undergraduate
degree in the same field) may have a different effect in some fields than in others,
while the latter makes the rather stringent assumption that a one-unit change in
an independent variable has the same effect on TTD for a student in chemistry,
for example, as it does for a student in the biosciences. A number of studies of
student aspirations and persistence suggest both assumptions are wrong (Biglan,
1973; Girves and Wemmerus, 1988; Thistlethwaite, 1962~. And economic
research suggests market conditions differ among scientific and engineering fields
(Berger, 1988; Freeman, 1971~. Failure to recognize that differences among field
exist can give rise to models that give inaccurate explanations of why TTD
changes.
The following sections provide field-specific data on the variables that
the opportunity-cost analysis and the literature suggest have an effect on AID.
The zero-order correlations are suggestive, since the actual relationship between
an independent variable and the dependent variable is captured by a model that
45
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tests their effect, holding all other things equal. These correlations highlight the
differences among fields and help to explicate the interrelationship of the
variables in each vector with TTD and its components. They also make it
possible to examine the relationship between TTD and variables for which data
are not available for sufficiently long periods of time.
Unless otherwise noted, all data are for the 1967-1986 period. All
correlations are between the selected variable and TTD and its components. A
single asterisk (*) denotes the correlation is significant at 1-percent level or
greater. A double asterisk (**) denotes a significance level of 5 percent.
Changes in Family Background Characteristics
Of particular interest are the percentage of graduates in each doctorate
cohort who are married (Table 4.1), the average number of dependents of
doctorates in each cohort (Table 4.2), the percentage who are black (Table 4.3),
the percentage who are Hispanic (Table 4.4), and the percentage who are women
(Table 4.5~.
Changes in Student Attributes
The variables of interest are average age of the cohort at the start of the
doctoral program (Table 4.6), percentage in the cohort who attended a highly
selective undergraduate school (Table 4.7), and percentage of the cohort with an
undergraduate degree in the same field as their doctorate (Table 4.~.
For the reasons discussed in Chapter 3, a thorough analysis of TTD
should employ a measure either of student ability, such as undergraduate or
graduate cumulative grade-point average,l2 or of achievement level, using scores
from the SAT, ACT, or ORE. Unfortunately, the DRF does not contain data
either on student grades or on predoctorate test scores. To develop a "proxy"
measure of the skills that a given cohort possesses, we used a variable equal to
the percentage of new doctorates in each cohort who attended a selective
undergraduate institution, where the average incoming 1973-74 freshmen earned a
combined SAT verbal and math score of 1,300 or higher. The assumption is
that the larger the percentage of students from institutions of this type, the larger
the overall ability level of the students in a given cohort.
12 Student grades pose a technical problem when they are aggregated at the
cohort level because the ordinal scales used to grade students at different
institutions are not additive.
46
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TABLE 4.1: Correlation for Percent Married, 1967-1986
Field l lo RTD TPGE TNEU
Chemistry -0.46** -0.67* -0.37 0.80*
Physics/Astronomy -0.68* -0.82* -0.59* 0.57*
Ea~/Atmospheric/Marine Sciences -0.44* * -0. 89* -0.08 0. 84*
Mathematics/Computer Sciences -0. 80* -0. 87* -0.74* -0.29
Engineering -0.69* -0.80* -0. 11 0.05
Agricultural Sciences -0.07* -0.86* -0.63* 0.68*
Biosciences -0.62* -0.92* -0.60* 0.78*
Health Sciences -0. 66* -0.80* -0.48* * -0.41
Psychology -0.82* -0.85* -0.85* -0.38
Economics -0.66* -0.91* -0.04 0.68*
Social Sciences -0.77* -0.93* -0.45** 0.65*
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
TABLE 4.2: Correlation for Average Number of Dependents, 1967-1986
Field
ITD RTD PAGE LIEU
Chemistry -0.66* -0.84* -0.42 0.76*
Physics/Astronomy -0.83* -0.91 * -0.64* 0.46* *
Earth/Atmospheric/Marine Sciences -0.48** -0.90* -0.03 0 . 8 5 *
Mathematics/Computer Sciences -0.84* -0.91* -0.74* -0.36
Engineering -0.85* -0.90* -0. 15 -0. 11
Agricultural Sciences 0 .04 -0.88* 0.72* O .7 8*
Biosciences -0.50** -0.88* -0.46** 0.85*
Health Sciences -0.5 8 * -0.74* -0.48* * -0.29
Psychology -0.74* -0.81 * -0.78* -0.24
Economics -0.47** -0.96* 0.18 0.85*
Social Sciences -0.71 * -0.92* -0.37 0.75*
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
47
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TABLE 43: Correlation for Percent Black, 1974-1986
Field 1-ID RTD TPGE INEU
Chemistry 0.09 0.008 -0.20 0.33
Physics/Astronomy 0.05 0.49 0.24 -0.48:
Earth/Atmospheric/Marine Sciences -0.007 0.25 -0.05 -0.59
Mathematics/Computer Sciences -0.20 -0.19 -0.27 -0.03
Engineering 0.25 0.47 -0.37 0.03
Agricultural Sciences 0.16 0.33 0.01 -0.13
Biosciences -0.09 -0.15 -0. 15 0.3 3
Health Sciences 0.01 0.06 -0.15 0.08
Psychology 0.57* 0.62** 0.53 0.46
Economics 0.60* 0.74* 0.55** -0.93*
Social Sciences 0.70* 0.75* 0.61** 0-.10
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
TABLE 4.4: Correlation for Percent Hispanic, 1974-1986
Field l lV RTD TPGE TNEI J
Chemistry 0.16 0.54 -0.14 -0.33
Physics/Astronomy 0.07 0.25 0.53** -0.40
Earth/Atmospheric/Marine Sciences 0.22 0.34 -0.03 -0.32
Mathematics/Computer Sciences 0.79* 0.73 * 0.73 * 0.53
Engineering 0.05 0.30 -0.49 -0.41
Agricultural Sciences 0.22 0.60** -0.26 -0.22
Biosciences 0.84* 0.86* 0.87* -0.17
Health Sciences 0.66* 0.62** 0.71* 0.52
Psychology 0.93 * 0.93 * 0.92* 0.91
Economics 0.68* 0.75* 0.41 -0.53
Social Sciences 0.89* 0.93* 0.83* 0.31
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
48
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TABLE 4.5: Correlation for Percent Female, 1967-1986
Field
l lV RID TPGE INAJ
Chemistry 0.63* 0.78* 0.48** -0.70*
Physics/Astronomy 0.68* 0.82* 0.69* -0.58*
Earth/Atmospheric/Marine Sciences 0.59* 0.92* 0.06 -0.76*
Mathematics/Computer Sciences 0.93 * 0.97* 0.86* 0.46**
Engineering 0.65* 0.72* -0.07 0.04
Agricultural Sciences 0.08 0.87* -0.67* -0.67*
Biosciences 0.70* 0.96* 0.68* -0.72*
Health Sciences 0.82* 0.88* 0.71* 0.58*
Psychology 0.91* 0.94* 0.93* 0.48**
Economics 0.63* 0.91* 0.03 -0.70*
Social Sciences 0.86* 0.96* 0.56* -0.57*
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
TABLE 4.6: Correlation for Average Age at Start of Doctoral Program, 1967-
1986.
Field TIN RTD TPGE luau
Chemistry 0.85* 0.89* 0.73* -0.51*
Physics/Astronomy 0.62* 0.61* 0.78* 0.23
Earth/Atrnospheric/hIarine Sciences 0.31 -Q.16 0.49* * 0.49 * *
Mathematics/Computer Sciences 0.93* 0.88* 0.91 * 0.65*
Engineering 0.29 0.08 0.83 * 0.42
Agricultural Sciences 0.44** -0.45** 0.75* 0.70*
Biosciences 0.90* 0.77* 0.91 * -0.11
Health Sciences 0.76* 0.61* 0.88* 0.65*
Psychology 0.99* 0.96* 0.98* 0.76*
Economics 0.72* -0.04 0.76* 0.42
Social Sciences 0.89* 0.61* 0.93* 0.19
.
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
49
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Table 4.7: Correlation for Percent from Selective Undergraduate Schools, 1967
1986
Field l lV RID TPGE TNAJ
Chemistry -0.61* -0.62* -0.40 0.27
Physics/Astronomy -0.55 * -0.43 -0.44* * -0.31
Earth/Atmospheric/~Iarine Sciences -0.30 -0.13 -0.29 -0.11
Mathematics/Computer Sciences 0.01 -0.003 0.11 -0.13
Engineering -0.25 -0.22 -0.37 -0.02
Agricultural Sciences -0.32 0.60* -0.56* -0.80*
Biosciences 0.30 0.19 0.37 0.01
Health Sciences -0.06 -0.13 -0.30 0.15
Psychology -0.39 -0.47** -0.42 0.02
Economics 0.11 0.11 0.08 -0.11
Social Sciences -0.70* -0.90* -0.34 0.68*
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
TABLE 4.8: Correlation for Percent with Undergraduate Degree in Doctoral
Field, 1974-1986
Field l lV RID TPGE TNEU
Chemistry -0.002 -0.06 0.07 0.22
Physics/Astronomy 0.76* 0.84* 0.45** -0.26
Earth/Atmospheric/Marine Sciences -0.29 0.67* -0.05 0.68*
Mathematics/Computer Sciences -0.82* -0.80* -0.83 * -0.40
Engineering -0.80* -0.89* -0.07 -0.02
Agricultural Sciences 0.28 -0.70* 0.65 * 0.85*
Biosciences 0.52* 0.89* 0.50* -0.85*
Health Sciences 0.77 0.83* 0.66* 0.57*
Psychology 0.07 0.16 0.08 -0.16
Economics 0.24 0.85* -0.27 -0.85*
Social Sciences 0.57* 0.79* 0.23 -0.69*
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
50
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Changes in Tuition and Financial Aid
The variables of interest here are average tuition and fees paid in a given
year (Table 4.9~; percentage of students with federal support (Table 4.10), private
foundation support (Table 4.11), research assistantships (Table 4.12), or teaching
assistantships (Table 4.13~; and percentage of students who relied on their own
earnings as their gnmary means of support (Table 4.14~.
Changes in Institutional Environment
This subsection examines the relationship between a select number of
aggregate measures of institutional environment and MID. These are the
percentage of students with a baccalaureate from a foreign institution (Table
4.15, p. 54), the ratio of full-iime equivalent faculty to doctorate recipients
(Table 4.16, p. 55), the ratio of the dollar value of government R&D
TABLE 4.9: Correlation for Average Tuition Paid
Field
llV
RID
IPGE
TNEU
Chemistry 0.07
Physics/Astronomy -0.007
EarthJAtmospheric/Marine Sciences -0.05
Mathematics/Computer Sciences -0.35
Engineering -0. 14
Agricultural Sciences 0.28
Biosciences -0.44* *
Health Sciences -0.26
Psychology -0.45**
Economics -0.54* *
Social Sciences 0.42
-0.05
-0.16
-0.30
-0.3 1
-0.15
-0.17
-0.39
-0.53
-0.40
-0.27
-0.33
0.05
0.12
-0.05
-0.36
0.27
0.17
-0.46
0.16
-0.46
-0.18
-0.54
0.33
0.38
0.40
-0.17
-0.10
0.36
0.09
0.21
-0.52*
-0.06
0.02
NOTES: (1) These are zero-order correlation coefficients. (2) Tuition lagged
three years. Weights were used to aggregate public end private institutions. Since
national averages are not available for graduate tuition and fees, our analysis
assumes that undergraduate tuition is a good proxy variable. The assumption is
that undergraduate and graduate tuitions are highly correlated and that increases in
the former are accompanied by similar increases in the latter.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
51
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TABLE 4.10: Correlation for Percent with Primary Support from Federal
Government, 1967- 1986
Field l lV RTD TPGE EMU
Chemistry -0.52** -0.70* -0.44 0.76*
Physics/Astronomy -0.51 * -0.67* -0.51 * 0.64*
Earth/Atmospheric/Marine Sciences -0.49* * -0.83 * -0.04 0.74*
Mathematics/Computer Sciences -0.87* -0.91 * -0.81 * -0.38
Engineering -0.61* -0.69* 0.14 -0.04
Agricultural Sciences -0.10 -0.59* 0.47* * 0.39
Biosciences -0.69* -0.94* -0.67* 0.72*
Health Sciences -0.74* -0.86* -0.48** -0.52**
Psychology -0.94* -0.94* -0.95* -0.60*
Economics -0.91 * -0.60* -0.47* * 0.20
Social Sciences -0.88 * -0.67 * -0.87 * -0.07
-
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
TABLE 4.11: Correlation for Percent with Primary Support from Private
Foundations, 1967- 1986
Field l lV RTD TPGE TNUJ
Chemistry -0.14 -0.18 0.06 0.05
Physics/Astronomy -0.58* -0.56* -0.21 -0.07
Earth/Atmospheric/Marine Sciences 0.01 -0.26 0.18 0.40
Mathematics/Computer Sciences -0.06 -0.23 0.03 0.26
Engineering -0.26 -0.38 -0.33 0.31
Agricultural Sciences 0.43 0.30 0.02 0.09
Biosciences 0.61* 0.18 0.59* 0.51**
Health Sciences -0.16 -0.24 -0.40 0.10
Psychology -0.56* -0.65 * -0.62* -0.07
Economics -0.02 -0.78* 0.43 0.86*
Social Sciences -0.21 -0.61* 0.24 0.90*
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
52
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TABLE 4.12: Correlation for Percent with Primary Support from Research
Assistantships, 1967-1986
.
.
Field TI,D RTD TPGE TNEU
Chemistry 0.63* 0.76* 0.46** -0.65*
Physics/Astronomy 0.60* 0.73* 0.56* -0.54*
Ear~/Atmospheric/Marine Sciences 0.33 0.82* -0.09 -0.88*
Mathematics/Computer Sciences 0.72* 0.75 * 0.72* 0.23
Engineering 0.79* 0.80* 0.09 -0.06
Agricultural Sciences -0.01 0.85 * - 0.66 * -0.77 *
Biosciences 0.77* 0.96* 0.74* -0.63*
Health Sciences 0.80* 0.91* 0.62* 0.58*
Psychology -0.64* 0.66 * -0.73 * -0.29
Economics 0.41 0.67* -0.09 -0.59*
Social Sciences 0.71* 0.77* 0.43 -0.39
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
TABLE 4.13: Correlation for Percent with Primary Support from Teaching
Assistantships, 1967-1986
Field
l lo RTD IPGE TNE]J
Chemistry 0.68* 0.72* 0.46** -0.38
Physics/Astronomy 0.87* 0.88* 0.48** -0.03
Earth/Atmospheric/Marine Sciences -0 .54* -0 . 61 * -0 . 24 0 .40
Mathematics/Computer Sciences 0.45 0.56* 0.31 O.1S
Engineering 0.66* 0.69* 0.43 0.09
Agricultural Sciences -0.02 0.65* -0.46** -0.61*
Biosciences 0.1 7 0. 64* 0.10 -O.8S*
Health Sciences 0.20 0.14 0.39 0.07
Psychology 0.04 0.10 0.04 -0.18
Economics 0.24 0.86* -0.29 -0.86*
Social Sciences 0.61* 0.81* 0.24 -0.65
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
53
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TABLE 4.14: Correlation for Percent with Primary Support from Own Earnings,
1977-1986
Field l lV RTD TPGE TNEU
Chemistry 0.63** 0.77* 0.11 0.25
Physics/Astronomy 0.52 -0.16 0.47 0.62
Earth/Atmospheric/Marine Sciences 0.71** 0.81* 0.40 0.14
Mathematics/Computer Sciences 0.81* 0.69** 0.72** 0.79*
Engineering -0.32 -0.32 -0.33 -0.08
Agricultural Sciences 0.66* * 0.31 0.49 0.77*
Biosciences 0.79* 0.73** 0.78* 0.63**
Health Sciences 0.92* 0.89* 0.93* 0.85*
Psychology 0.84* 0.85* 0.81 * 0.78*
Economics 0.66** 0.79* 0.05 -0.46
Social Sciences 0.91* 0.92* 0.84* 0.86*
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
TABLE 4.15: Correlation for Percent with B accalaureate from Foreign
Institutions, 1967-1986
Field l lV RTD TPGE TNEU
Chemistry 0.42 0.34 0.14 0.19
Physics/Astronomy 0.32 0.17 0.07 0.53*
Earth/Atmospheric/hIarine Sciences 0.22 -0.13 0.40 0.41
Mathematics/Computer Sciences 0.90* 0.90* 0.88* 0.50*
Engineering 0.76* 0.74* 0.70* 0.16
Agricultural Sciences 0.21 -0.29 0.32 0.41
Biosciences -0.52** -0.69* -0.53* 0.51*
Health Sciences -0.46** -0.45 * * -0.18 -0.48* *
Psychology -0.28 -0.27 -0.34 -0.09
Economics 0.68* 0.53* 0.35 -0.29
Social Sciences -0.32 -0.42 0.19 0.38
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
54
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TABLE 4.16: Correlation for Number of Full-Time Equivalent Faculty
l
Field l ill) RID TPGE LIEU
Chemistry 0.68* 0.85* 0.37 -0.65*
Physics/Astronomy 0.88* 0.95* 0.65* -0.33
Eard~lAtmosphericIMarine Sciences 0 .3 8 0 . 82* -0.09 -0 . 81 *
Mathematics/Computer Sciences 0.80* 0.90* 0.69* 0.33
Engineering 0.79* 0.93* 0.19 -0.14
Agricultural Sciences -0.06 0.83* -0.66* -0.79*
Biosciences 0.28 0.75* 0.25 -0.91*
Health Sciences 0.48 0.60* 0.49 0.19
Psychology 0.60* 0.69* 0.64* 0.04*
Economics 0.22 0.90* -0.37 -0.92*
Social Sciences 0.52** 0.83* 0.11 -0.85*
NOTES: (1) These are zero-order correlation coefficients. (2) Period for AD is
1967-1986; FACULTY, a crude proxy for the number of mentors available to
doctorate students, is lagged, 1964-1983.
*Denotes correlation is statistically significant at 1 percent level or greater.
**Denotes correlation is significant at 5 percent level or greater.
TABLE 4.17: Correlation for Government R&D Spending
Field l lo RID TPGE TNEU
Chemistry 0.54* 0.70* 0.47* -0.72*
Physics/Astronomy 0.59* 0.73 * 0. 64* -0.61 *
Earth/Atmospheric/Marine Sciences 0.63* 0.92* 0.07 -0.72*
Mathematics/Computer Sciences 0.92* 0.91* 0.90* 0.49**
Engineering 0. 62* 0.71 * -0.14 0.01
Agricultural Sciences 0.18 0.86* -0.56* -0.60*
Biosciences 0.80* 0.98* 0.79* -0.63*
Health Sciences 0.89* 0.95* 0.67* 0.70*
Psychology 0.97 * 0.98 * 0.97 * 0.63 *
Economics 0.75* 0.89* 0.14 -0.61*
Social Sciences 0.95 0.96* 0.71* -0.40
NOTES: (1) These are zero-order correlation coefficients. (2) Period for AD is
1967-1986 and for R&D is 1964-1983.
*Denotes correlation is statistically significant at 1 percent level or greater.
**Denotes correlation is significant at 5 percent level or greater.
55
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TABLE 4.20: Correlation for Percent with Graduate Degree from Category I or
Category II Research School, 1967-1986
Field l lV RTD TPGE TNEU
Chemistry 0.03 0.20 0.17 -0.64*
PhysicstAstronomy 0.13 0.27 0.25 -0.59*
Earth/Atmospheric/Marine Sciences -0;46** -0.79* -0.02 0.66*
Mathematics/Computer Sciences -0.17 -0.13 -0.13 -0.38
Engineering -0.14 -0.06 -0.53 * -0.08
Agricultural Sciences -0.17 -0.47** 0.18 0.29
Biosciences 0.003 -0.44** 0.04 0.74*
Health Sciences - 0.15 - 0.33 - 0.23 0.06
Psychology -0.79* -0.85* -0.82* -0.26
Economics 0.17 -0.63* 0.67* 0.77*
Social Sciences -0.68* -0.87* -0.38 0.67*
NOTES: These are zero-order correlation coefficients. Category I Research
University is taken from the Carnegie Classification of Colleges and Universities.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
TABLE 4.21: Correlation for Percent with Graduate Degree from "Top 40"
School, 1967-1986
Field ~ lV RTD TPGE TNEU
Chemistry -0.16 0.01 0.02 -0.58*
Physics/Astronomy 0.17 0.32 0.25 -0.58*
EarthtAtmospheric/Marine Sciences 0.005 0.14 -0.29 -0.20
Mathematics/Computer Sciences 0.08 0.10 0.12 -0.19
Engineering -0.46** -0.47* * -0.50* * -0.02
Agricultural Sciences -0.28 -0.82* 0.26 0.53*
Biosciences 0.05 -0.29 0.05 0.56*
Health Sciences -0.08 -0.28 -0.17 0.16
Psychology -0.80* -0.87$ -0.84* -0.29
Economics 0.35 -0.40 0.72* 0.59*
Social Sciences -0.45* -0.73* -0.09 0.77*
NOTES: These are zero-order correlation coefficients. "Top 40" refers to those
schools so identified in the NRC's Assessment of Research Doctorate Programs in
the United States.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
58
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\
TABLE 4.22: Correlation for Average Salary of Recent Doctorate Recipients
Field TID RTD TPGE EMU
Chemistry 0.70* 0.79* 0~40 -0.50**
Physics/Astronomy 0.67* 0.62* 0.25 0.23
Ear~/Atmospheric/hIarine Sciences -0.57* -0.52** -O.28 0.19
Mathematics/Computer Sciences 0.49** 0.59* 0.35 0.24
Engineering 0.78 * 0. 84* 0 .40 0. 02
Agricultural Sciences -0.20 -0.86* 0.57* 0.57*
Biosciences -0.73* -0.96* -0.73* 0.70*
Health Sciences -0.80* -0.82* -0.60* -0.70*
Psychology -0.96* -0.97* -0.97* -0. 60*
Economics -0.68* -0.37 -0.53* 0.05
Social Sciences -0.89* -0.97* -0.63* 0.52**
NOTES: (1) These are zero-order correlation coefficients. (2) Specifically, SDR
salary is regressed on weekly eamings, and the coefficients from this regression
are used to estimate salaries in the missing years; SDRSAL is lagged three years.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
TABLE 4.23: Correlation Between SALRAT1 and TTD and Its Components
Field
llV
RTD
TPGE
TNEU
Chemistry -0.69* -0.87* -0.43 0.7 1 *
Physics/Astronomy -0.59* -0.75* -0.52* 0.54*
Ear~/Atmospheric/Marine Sciences -0.007 0 .10 -0.002 -0 .13
Mathematics/Computer Sciences -0. 87* -0.95 * -0.78* -0.3 7
Engineering -0.75 * -0. 85 * 0.08 0.04
Agricultural Sciences 0.18 0. 66* -0.37* -0.47* *
Biosciences 0.60* 0.91* 0.57* -0.77*
Health Sciences 0.38 0.34 0.42 0.32
Psychology 0.76* 0.76* 0. 80* 0.44**
Economics 0.41 0.56* 0.20 -0.39
Social Sciences 0.23 0.29 0.19 -0.25
NOTES: (1) These are zero-order correlation coefficients. (2) The years prior to
1973 are projected; SALRAT1 is lagged three years.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
59
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TABLE 4.24: Correlation for Salary Ratio of Doctorates 10 Years After Degree
Field l lV RID TPGE LIEU
Chemistry
Physics/Astronomy
Ear~/Atmosphenc/Marine Sciences
Mathematics/Computer Sciences 0.56
Engineenng 0.55
Agncultural Sciences
Biosciences
Health Sciences
Psychology
Economics
Social Sciences
0.63
0.62
-0.51
0.72*
0.57*
0.63*
0.63*
0.5 1**
0.34
-0.56*
0.14
0.42 0.33
0.13 0.01
-0.6 1 * -0.56* -0.26
0.21 0.07 -0.01 -0.01
NOTES: (1) These are zero-order correlation coefficients. (2) A comparison is
made to the baccalaureate rather than the master's salary because of the larger
number of observations in the former category; SALRAT10 is lagged Tree years.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
Employment Indicator Variables
The percentage of doctorate recipients seeking postgraduate employment
is a reliable indicator of job market opportunity. Job opportunities, in turn, are
likely to affect TTD. Data on job-seeking behavior are easy to obtain and
reasonably reliable (Tables 4.2~4.30~. However, because such data are collected
at the time the doctoral candidate is completing the degree, they may understate
employment prospects, because finding a job after graduation takes time. Data
on job-seeking activity have been used in studies by Freeman (1971~.
The Stock Variable
The zero-order correlations between TTI) and its components and the
number of doctorates in the United States divided by the U.S. population are
shown in Table 4.31.
60
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TABLE 4.26: Correlation for Percent Seeking Postgraduate Employment
Field
llV
RTD
TPGE
TN~
Chemistry 0.62*
Physics/Astronomy 0.7S*
Earth/Atmospheric/Marine Sciences -0.02
Mathematics/Computer Sciences 0.30
Engineering 0.65 *
Agricultural Sciences 0.20
Biosciences 0.24
Health Sciences 0.51 *
Psychology 0.74*
Economics 0.19
Social Sciences 0.84*
0.58*
0.60*
0.42
0.41
0.62*
0.80*
0.61*
0.55*
0.78*
0.75*
0.95*
0.44*
0.36
-0.12
0.12
0.55*
-0.39*
0.19
0.59*
0.78*
-0.33
0.54*
-0.17
0.44**
-0.60*
0.11
0.24
-0.60*
-0.71*
0.27
0.30
-0.72*
-0.58*
NOTES: (1) These are zero-order correlation coefficients. (2) SEEK variable is
lagged three years.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
TABLE 4.27: Correlation for Percent with Definite Employment or
Postdoctoral Appointment
Field
l lV RTD TPOE ~J
Chemistry -0.64*
Physics/Astronomy -0.75 *
Earth/Atmospheric/hIarine Sciences -0.02
Mathematics/Computer Sciences -0.31
Engineering -0.63 *
Agricultural Sciences -0.20
Biosciences -0.1 ~
Health Sciences -0.62*
Psychology -0.71 *
Economics -0.09
Social Sciences -0.82*
-0.61*
-0.61*
-0.44**
-0.43
-0.60*
-0.77*
-0.54*
-0.67*
-0.75*
-0.66*
-0.95*
-0.45**
-0.38
0.15
-0.14
-0.53*
0.37
-0.11
-0.62*
-0.75 *
0.33
-0.52*
0.19
-0.37
0.60*
-0.09
-0.24
0.56*
0.68*
-0.36
-0.26
0.66*
0.60*
NOTES: (1) These are zero-order correlation coefficients. (2) DEFIN variable is
lagged three years.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
62
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TABLE 4.28: Correlation for Overall U.S. Unemployment Rate
Field T1D RTD TPOE TNAJ
Chemistry 0.55* 0.61* 0.61* -0.55*
Physics/Astronomy 0.61 * 0.64* 0.63 * -0.28
Earth/Atmospheric/hIarine Sciences 0.39 0.73* 0.15 -0.72*
Mathematics/Computer Sciences 0.81* 0.77* 0.73* 0.57*
Engineering 0.54* 0.63* -0.15 0.06
Agricultural Sciences 0.18 0.71 * -0.37 -0.51 *
Biosciences 0.71* 0.82* 0.69* -0.47*
Health Sciences 0.72* 0.81* 0.50** 0.53*
Psychology 0.78* 0.78* 0.82* 0.52*
Economics 0.61* 0.71* 0.07 -0.44**
Social Sciences 0.77* 0.78* 0.63* -0.34*
NOTES: (1) These are zero-order correlation coefficients.
variable is lagged three years.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
(2) Unemployment
TABLE 4.29: Correlation for Unemployment Rate of College-Educated
Population
Field l lo RID TPGE EMU
Chemistry 0.58 * 0.63 * 0.63 * -0.57*
Physics/Astronomy 0.74* 0.73* 0.68* -0.15
Earth/Atmospheric/bIarine Sciences 0.38 0.70* 0.16 -0.69*
Mathematics/Computer Sciences 0.77* 0.78* 0.67* 0.48**
Engineering 0.68* 0.74* 0.02 0.14
Agricultural Sciences 0.14 0.73* -0.39 -0.58*
Biosciences 0.58* 0.78* 0.54* -0.55*
Health Sciences 0.63* 0.73* 0.47** 0.42
Psychology 0.70* 0.71* 0.75* 0.39
Economics 0.44** 0.72* -0.07 -0.55*
Social Sciences 0.67* 0.76* 0.48** -0.47**
NOTES: (1) These are zero-order correlation coefficients.
rate is lagged three years.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
63
(2) Unemployment
OCR for page 64
TABLE 4~30: Correlation Between Percent Seeking Postgraduate Employment
and the Other Market Variables
Between SEEK and
.
Field I3NEMP* UNEMP4YR**
Chemistry 0.43 0.65
Physics/Astronomy 0.41 0.60
Ear~/Atmospheric/Marine Sciences 0.55 0.71
Mathematics/Computer Sciences 0.36 0.56
Engineering 0.40 0.5 8
Agricultural Sciences 0.72 0.85
Biosciences 0.64 0.80
Health Sciences 0.69 0.82
Psychology 0.81 0.88
Economics 0.70 0.82
Social Sciences 0.88 0.88
*UNEMP = Overall unemployment rate for the U.S. labor force (obtained from He
Bureau of Labor Statistics)
**UNEMP4YR = Unemployment rate for persons with four or more years of
college (obtained from the Bureau of Labor Statistics)
TABLE 4.31: Correlation for Per Capita Number of Doctorates in the United
States, 1967-1986
Field l lV RTD TPOE TOFU
Chemistry -0.71* -0.82* -0.49* * 0. 62*
Physics/Astronomy -0. 87* -0.93 * -0.63* 0.3 0
Earth/Atmospheric/Marine Sciences -0 .47 * -0 . 89 * -0.010 0 . 84 *
Mathematics/Computer Sciences -0. 8 7 * -0. 91* -0.7 8 * -0.44*
Engineering -0.83* -0.91* -0.16* -0.06
Agricultural Sciences -0.05* -0.70 0.36 0.63*
Biosciences -0.59* -0.87* -0.54** 0.70*
Health Sciences -0.38 -0.38 -0.11 -0.39
Psychology -0.91* -0.89* -0.91 * -0.68*
Economics -0.46** -0.91* -0.1 7 0.79 *
Social Sciences -0.85* -0.84* -0.67* 0.3 6
NOTE: These are zero-order correlation coefficients.
*Denotes correlation is statistically significant at 1% level or greater.
**Denotes correlation is significant at 5% level or greater.
64
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The Zero-Order Correlation of the Vectors
The correlations between I-l ~ and all of the variables in each vector for
which data are available for 1967-1986 are in Table 4.32. Regression analysis
was used to derive an adjusted R2 for each vector on the assumption that this is
Me only vector that affects l-! ~ (no one model consistently has the highest Rat.
The F vector (family background charactenstics) explains most of the adjusted
variation in TTD in math, health sciences, and social sciences. The I vector
(individual attributes) explains most of the variation in chemistry, engineering,
and psychology. Variations in two fields agricultural sciences and
biosciences are best explained by the TLFA vector (tuition and financial aid).
Finally, the O vector (organizational factors) explains most of IlD's adjusted
variation in the remaining three fields: P&A; EAM; and economics.
Remarkably, the E vector (economic variables) was not able to predict a larger
amount of the variation than other vectors in any fields.
TABLE 432: Amount of Adjusted Variation in TTD Explained by Each of the
Five Vectors
Vector
Field F I TLFA O E
Chemistry 0.73* 0.76* 0.75* 0.71* 0.48
Physics/Astronomy 0.80* 0.77* 0.81* 0.84* 0.76*
Ear~/Atmospheric/Marine Sciences 0.33** 0.29** 0.44* 0.66* 0.18
Mathematics/Computer Sciences 0.96* 0.86* 0.93* 0.95* 0.89*
Engineering 0.71 * 0.85* 0.57* 0.78* 0.63 *
Agricultural Sciences 0.11 0.09 0.34** 0.31 -0
Biosciences 0.82* 0.82* 0.94* 0.84* 0.50
Health Sciences 0.91* 0.75* 0.71* 0.83* 0.41*
Psychology 0.97* 0.98* 0.94* 0.95* 0.59*
Economics 0.76* 0.64* 0.88* 0.89* 0.17
Social Sciences 0.98* 0.91* 0.95* 0.92* 0.67*
NOTE: F = Family Background (MARRIED, DEPEND, TEMP, WOMEN); I = AGE,
SAMEFLD, SELECT; TLFA = TUITION, SUPPED, SUPPRIV, SUPTA, SUPRA; 0 =
FORBACC, BTOP40, BCARN1ST, PTOP40, PCARN1ST, FACULTY, R&D; E =
SALRAT1, UNEMP4YR, SEEK. Acronyms are defined in Appendix B. pp. 175-
177.
*Denotes correlation statistically significant at 1% level or greater.
**Denotes correlation significant at 5% level or greater.
65
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TABLE 4.33: Number of Fields in Which Each Variable Had a Statistically
Significant Correlation with AD or RTD
TTD RTD
Negative Positive Negative Positive
Correlation Correlation Correlation Correlation
Family Background Characteristics
MARRED 10 0 11 0
DEPEND 10 0 11 0
BLACK 0 3 0 3
HISPANIC 0 6 0 7
WORN O 1 0 0 1 1
Student Attributes
AGE 0 9 1 7
SELECI 3 0 4 0
SAMEFLD 2 3 3 6
Tuition and Financial Aid
TUllION ~ 3 0 1 0
SUPPED 1 0 0 1 1 0
SUPPRIV 2 1 4 0
SUPRA 1 7 0 1 1
SUPTA 1 4 1 8
SUPOWN O 9 0 8
Institutional Environment
FORBACC 2 3 2 3
FACULTY 0 8 0 11
R&D 0 9 0 11
BCARN1ST 1 2 2 1
BTOP40 3 1 4 1
PCARN1ST 3 0 6 0
PTOP40 3 0 4 0
Salary Variables
SDRSAL 7 3 6 4
SALRAT1 4 2 4 4
Employment Conditions
SEEK 0 6 0 10
D1EFIN 6 0 10 0
UNEMP O 9 . 0 11
UNEMP4YR 0 9 0 1 1
PERPOP
Stock Variable
10 0 9 0
NOTES: (1 ) These are zero-order correlation coefficients. (2) Statistical
significance is at the .05 level. (3) Acronyms are defined in Appendix B. pp. 175-
177.
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Summary
Table 4.33 shows the number of fields with which each of the
independent variables had a statistically significant correlation (p = .05) to time
to the doctorate. The table is limited to zero-order correlations with T1 D and its
component RTD, since other components did not appear to increase TTD.
The greatest correlation to I1D was for variables indicating marital
status, dependents, gender, and federal financial support. These correlations were
apparent in 10 fields for 11D and in all 11 fields for RTD. As predicted by the
opportunity-cost analysis, married members of the cohort and cohort members
with dependents had a negative correlation to DID. Those with federal support
also showed a negative correlation to TTD, which was not predicted. Female
gender was positively correlated to 1-1~.
Other variables that were strongly and positively correlated with RTD
in all fields were research assistantships, number of full-time faculty, level of
federal R&D support, the overall unemployment rate, and the unemployment
rate for college graduates. The signs were not always as predicted; for example,
the relation between the unemployment variables and RTD was expected to be
negative but turned out positive.
Zero-order correlations must be approached with some caution. While
they are useful for demonstrating an association between ICED and/or its
component parts and the variables posited by the literature and by opportunity-
cost hypotheses, the nature of He relationship is speculative. In addition, some
of"the independent variables are time-dependent and may move up or down
together over long periods.
67
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Representative terms from entire chapter:
rtd tpge
