Are international election observation missions able to deter election-day fraud?

The question I would like to answer relates to the “effect of international election observation on election-day fraud”. This means trying to discover the influence of the simple presence of observers on the behaviour of candidates, electoral staff, and voters. Even if proponents of election observation promote this instrument claiming its potential to reduce fraud, that capability (that must first be proved) can be classed among the “unintended consequences” of international election observation, since the stated role of observers is simply to “observe and report” on an electoral process. Its potential is to reassure the electorate that it is safe for them to vote and run for office and/or to deter fraud. While this is a fundamental element of the role of observers, it is not technically part of the observers’ job. They are some of the “positive” spill-over effects or unintended consequences, something that the mere presence of observers can provoke under certain circumstances without explicitly meaning to