 39. Ecological Sampling Methods  811
situation perceptions relate to personality 
states in daily life. They assessed situation 
perceptions and self-  reported personality 
states up to eight times a day between 9:00 
A.M. and 11:00 P.M. on 7 consecutive days 
among 210 undergraduate students. In this 
study, participants received text messages 
containing a personalized link to the Web-
based questionnaire that they answered on 
their own smartphones. This study restrict -
ed participation to people who owned an ap -
propriate smartphone with mobile Internet 
access. The results showed that personality 
traits and perceived situational characteris -
tics predict personality states; for example, 
trait emotionality and perceived adversity 
and negativity of the situation predicted that 
people reported behaving more nervously. In 
contrast, results did not support the hypoth -
esis that traits and situation perceptions dy -
namically interact in shaping (self-  reported) 
behavioral states (Sherman et al., 2015).
In summary, repeated self-  reports of emo -
tions, thoughts, perceived behavior, and ex -
perienced situations in daily life have been 
successfully used in personality research 
over the last decades and have contributed 
greatly to understanding how personal -
ity manifests and matters in the real world. 
These studies showed considerable consis -
tency of personality states across diverse 
situations and also meaningful covariation 
of situations and states, which are partly 
moderated by personality traits. Thus, the 
studies meet the criteria of assessing expe -
riences in vivo across a range of naturally 
occurring settings and in (close to) real time. 
At the same time, they rely on participants’ 
self- perceptions, which can be considered 
the “gold standard” for assessing “inner” 
thoughts and experience but might be subop -
timal, relative to direct behavioral observa -
tion, for assessing “outer” behavior (Vazire, 
2010; Robins, Chapter 26, this volume).
Ecological Assessment of Daily Behavior
Several methods allow for the real-world as -
sessment of daily behavior (Wrzus & Mehl, 
2015). On the one hand, experience sampling 
can be used to study self-  reported momen -
tary behavior. As mentioned, this approach 
has proven successful, for example, in study -
ing personality stability and variability from the perspective of traits as density distribu -
tions of states (Fleeson & Gallagher, 2009; 
McCabe & Fleeson, 2016; Noftle & Fleeson, 
2010). On the other hand, studying momen -
tary personality-  related behaviors through 
the lens of participants’ self-  perceptions still 
renders their responses subject to self-  report 
limitations such as impression manage -
ment, self-  deception, and lack of awareness 
(e.g., verbal mannerisms, automatic expres -
sive behaviors). Observational methods can 
help bypass these limitations (Furr, 2009). 
Whereas behavioral observation in the labo -
ratory is relatively straightforward, assess -
ing behavior in daily life is more challenging 
(Wrzus & Mehl, 2015). Two decades ago, 
the comprehensive observational assess -
ment of a person’s daily behavior was close 
to impossible (Craik, 2000). Since then, the 
mobile device revolution unfolded and has 
rendered the collection of comprehensive, 
real-world behavioral data more feasible 
(Harari, Müller, et al., 2017; Harari et al., 
2020; Kosinksi & Behrend, 2017).
The scientific desire to capture humans 
directly in the pursuit of their lives is not 
new. Webb, Campbell, Schwartz, Sechrest, 
and Grove (1981) reviewed early creative 
attempts to study behavior nonreactively 
through both direct observation and indi -
rect trace measures. The field of ecological 
psychology set out to study “human behav -
ior and its environment in situ ” through 
“specimens” collected from the “continu -
ous stream of a person’s behavior” (Barker, 
1968, p. 1), with its most prominent product 
being Barker and Wright’s (1951) unique, 
book-  length observational record of 1 day in 
the life of 7-year-old Raymond Birch. Craik 
(2000) later built on this seminal study with 
his Lived Day Analysis, in which he followed 
a participant for 1 day with a handheld video 
camera to describe and analyze her lived day.
The challenge for naturalistic observation 
research has been to translate the rich ideas 
that ecological psychology developed within 
case studies into larger, empirical research 
realities. In pioneering studies on behavioral 
residues, observers rated people’s personal 
spaces to draw conclusions on the personal -
ity of the inhabitants (Gosling, Jin Ko, Man -
narelli, & Morris, 2002; Gosling, Craik, 
Martin, & Pryor, 2005). Several new meth -
ods facilitate the intermittent or (nearly) 
continuous sampling of everyday behavior.