 14. Personality in Young Adulthood  325
ness than participants who remained single 
across the study period.
Neyer and Lehnart (2007) followed up on 
and extended this study by using the same 
sample to examine the effects of the first ro -
mantic relationship on personality change 
across three measurement waves over 8 
years. The inclusion of a third measurement 
wave allowed them to compare personality 
trait changes among four different groups of 
young adults: stable singles (participants who 
remained single across 8 years), early begin -
ners (participants who were in stable roman -
tic relationship across the 8-year research 
period), timely beginners (participants who 
entered into a romantic relationship between 
the first two measurement occasions), and 
late beginners (participants who entered into 
a romantic relationship between the last two 
measurement occasions). With one exception, 
the results were largely similar to the find -
ings by Neyer and Asendorpf (2001). Early, 
timely, and late beginners showed decreases 
in neuroticism and increases in extraversion 
after they entered into a serious romantic re -
lationship, whereas stable singles remained 
stable on these traits throughout the 8-year 
period. Notably, the effects of relationship 
formation on conscientiousness did not rep -
licate in the group of late beginners.
The effect of romantic relationship forma -
tion on neuroticism was replicated in anoth -
er 8-year study with participants from the 
United States. The study was comparable in 
terms of longitudinal design and age group 
but focused on changes in neuroticism only 
(Lehnart, Neyer, & Eccles, 2010). Com -
pared to stable singles, young adults who 
entered a romantic relationship for the first 
time showed decreases in facets of neuroti -
cism such as depression and social anxiety.
A potential limitation of the studies by 
Neyer and colleagues (and research on life 
transitions in general) concerns the problem 
that random assignment of participants to 
different life transitions or no transitions is 
usually not feasible or ethical. People typi -
cally select themselves into certain relation -
ships, roles, and environments. In other 
words, the experience (or nonexperience) of 
most life transitions may reflect selection ef -
fects. Consequently, putative effects of the 
life transitions are confounded with preex -
isting group differences (Foster, 2010). For 
instance, singles and individuals who enter a relationship have been found to differ in 
a number of demographic and psychologi -
cal characteristics, including their person -
ality traits (e.g., Neyer & Lehnart, 2007). 
To the degree that these preexisting group 
differences drive the observed differences in 
personality trait change, causal interpreta -
tions of romantic relationship effects on trait 
change would be compromised.
Wagner, Becker, Lüdtke, and Trautwein 
(2015) aimed to address this problem by 
providing a more rigorous test of the effects 
of the first partnership experience on per -
sonality change. Specifically, they used pro -
pensity score matching techniques (Rosen -
baum & Rubin, 1983; Thoemmes & Kim, 
2011) to integrate the information on ob -
served covariates to create matched samples. 
These samples differed statistically only 
with regard to the experience of the particu -
lar life transition of interest. Using matched 
samples and 4-year longitudinal data, the 
results of this study only partially replicated 
the findings of previous research on the im -
pact of the transition to the first romantic 
relationship on personality change. Specifi -
cally, the first partnership experience was 
related to higher extraversion and conscien -
tiousness and to lower neuroticism only in 
participants who had their first partnership 
experience between ages 23 and 25, but not 
in participants who established their first 
partnership between ages 21 and 23.
In addition to research on personality 
change in the context of romantic relation -
ship transitions, a handful of longitudinal 
studies has examined whether marriage 
stimulates changes in newlyweds’ person -
ality traits. For example, Neyer and Asen -
dorpf (2001) compared the personality trait 
changes of unmarried participants who were 
in a romantic relationship ( N = 176) with 
those who got married ( N = 67) during the 
4-year research period. This study found no 
differences between married participants 
and participants in a romantic relationship.
Specht and colleagues (2011) addressed 
the question whether marriage is related to 
personality change in a large-scale nation -
ally representative longitudinal study. Using 
two-wave longitudinal data, they compared 
Big Five trait changes in married participants 
(N = 664) with those in participants who did 
not get married during the 4-year research 
period ( N = ~14,000). They found that in -