  There have been recent calls for research on the human side of software
engineering and its impact on various factors such as productivity, developer
happiness and project success. An analysis of which challenges in software
engineering teams are most frequent is still missing.
  We aim to provide a starting point for a theory about relevant human
challenges and their causes in software engineering. We establish a reusable
set of challenges and start out by investigating the effect of team
virtualization. Virtual teams often use digital communication and consist of
members with different nationalities.
  We designed a survey instrument and asked respondents to assess the frequency
and criticality of a set of challenges, separated in context "within teams" as
well as "between teams and clients", compiled from previous empiric work, blog
posts and pilot survey feedback. For the team challenges, we asked if
mitigation measures were already in place. Respondents were also asked to
provide information about their team setup. The survey also measured Schwartz
human values. Finally, respondents were asked if there were additional
challenges at their workplace.
  We report on the results obtained from 192 respondents. We present a set of
challenges that takes the survey feedback into account and introduce two
categories of challenges; "interpersonal" and "intrapersonal". We found no
evidence for links between human values and challenges. We found some
significant links between the number of distinct nationalities in a team and
certain challenges, with less frequent and critical challenges occurring if 2-3
different nationalities were present compared to a team having members of just
one nationality or more than three. A higher degree of virtualization seems to
increase the frequency of some human challenges.
