  Background: Due to the societal, economic, and health costs of COVID-19
non-pharmaceutical interventions (NPIs), it is important to assess their
effects. Human mobility serves as a surrogate for human contacts and compliance
to NPIs. In Nordic countries, NPIs have mostly been advised and sometimes made
mandatory. It is unclear if making NPIs mandatory further reduced mobility.
  Aim: We investigated the effect of non-compulsory and follow-up mandatory
measures in major cities and rural regions on human mobility in Norway. We
identified NPI categories that most affected mobility.
  Methods: We used mobile phone mobility data from the largest Norwegian
operator. We analysed non-compulsory and mandatory measures with before-after
and synthetic difference-in-differences approaches. By regression, we
investigated the impact of different NPIs on mobility.
  Results: Nationally and in less populated regions, follow-up mandatory
measures further decreased time, but not distance travelled. In urban areas,
however, follow-up mandates also decreased distance, and the effect exceeded
that of initial non-compulsory measures. Stricter metre rules, gyms closing and
reopening, restrictions on guests in homes, and face mask recommendations most
impacted distance travelled. Time travelled was most affected by gyms closing
and restaurants and shops reopening.
  Conclusion: Overall, non-compulsory measures appeared to decrease distance
travelled from home, while mandates further decreased this metric in urban
areas. Time travelled is reduced more by mandates than by non-compulsory
measures for all regions and interventions. Stricter distancing and restricted
number of guests were associated with decreases in mobility.
