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connectivity within the entering group itself (in the i rst column 18.191 compared to 8.729
for the exiting group), but also with respect to the linkages with the permanent group (in
the second column 7.592 compared to 6.738 for exit). While the former observation, that
entrants are a more homogeneous group, is signii cant, the latter is not at an acceptable
level of signii cance ( p -value of 0.208). The values in the second and third column are
based on the same number of connections but in calculating the mean they are divided
by a dif erent number of focal actors. Accordingly, we notice more technological con-
nections between the permanent innovators and the entering innovators (37.250) as
compared to the exiting group (22.531). The permanent innovators themselves increase
their technological overlap signii cantly between the two periods from 15.125 to 19.563
(fourth column).
With respect to our previous result of an increasing cohesion of the network of tech-
nological overlap, the i ndings here indicate that both the permanent innovators as well
as the entrants (compared to the exiting innovators) tend to increasingly concentrate
on the technological core competencies of the network as a whole. And with respect to
the increasing connectedness of the pr -network, we presume that the permanent actors'
degree of cooperation should have increased between P1 and P2, and the degree of coop-
eration with entrants should have been higher than with exiters.
Entry and exit to the network
In order to develop further on this presumption, we compute mean degrees for several
groups of actors in both periods with respect to personal relationships. We again distin-
guish between relationships based on cooperations ( co ) and on scientist mobility ( sm ).
The respective results are stated in Tables 17.5 and 17.6.
Table 17 . 5
Cooperation: mean degree (within and between blocks)
Within
Between
Between
Within
P1
Exit
Exit and
permanent
Permanent
and exit
Permanent
N
107
107
32
32
Mean degree
3.084
0.710
2.375
2.563
Standard deviation
(5.207)
(1.873)
(5.375)
(5.346)
P2
Entry
Entry and
permanent
Permanent
and entry
Permanent
N
157
157
32
32
Mean degree
2.242
1.516
7.438
3.938
Standard deviation
(4.424)
(2.623)
(17.005)
(6.710)
Signii cance of dif erence between mean degrees
Mann-Whitney
Wilcoxon rank sum test
W
9191.5
7111
34.5
49
p - value
0.066
0.003
0.136
0.100
Note: One-sided tests are performed with H 0 as no dif erence between samples and H 1 in the direction of the
observed dif erences.
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