I'm asking this from the perspective of the future supervisor. After a round of interviews I approached the highest ranked candidate. My error was not including a deadline in the initial email.
Now a week has passed from the last response I got from the candidate. I have sent another reminder recently. However, my patience is running out. I understand that of course the candidate might be trying to buy some time to make up their mind, and probably waiting for other offers.
Are there any other options apart from sending an ultimatum? If so, how much longer should I wait to filter out external reasons for the lack of responses? I.e. sickness, unforeseen events, etc.? This is in Europe.