How do you answer 'can you tell us about a time you have made a decision which affected your team or group of people.?

This is a standard "job interview" question. Many think you can only answer it if you've been actually employed, this is not necessarily the case.

If you have been employed consider where for any reason you have had to make a decision on your own (i.e. used your initiative!)

What was the issue?. what decision did you make? Was it affecting just you or would it have affected more than one person?

In a working situation , even at basic level we make decisions all the time based on initiative and knowledge of the role your in.

Simple Example: There is a warning just announced on the radio that local utility company is switching off the water in an hours time and you've heard it on the radio. You take it upon your self to find some buckets and bottles - you fill these quickly and pace bottles in a canteen /kitchen are a safely and the buckets in the bathroom area for toilet use ./ cleaning.

The water is off and no one else has done anything you however have provided an emergency resource of water for a temporary shut down which his highly likely to allow the business around you to still function. Not only has your decision affect you but others

In a non-work based environment.

You play in a school orchestra - You are due to play that evening at an event and notice a box carrying all the manuscripts has been left on a shelf. No sure if these are are just extra copies of they are the essential ones you take them with you - That night it's realised that the "box" is not there - you provide it.

or

You are out at a venue (perhaps watching a film) the bus you are due to take home has not arrived. You ring home to tell parents etc but there is no answer, you have remembered to take additional numbers of trusted people who you can ring and ask them to inform your parents what has happened.

The question is not a trick question. Its set up to see if you have the ability to make judgements based on a situation and do your best to follow either a procedure or to make a decision that is not covered by a standard procedure. The interviewer/question is testing your "Problem Solving Skills". They are also seeing if you have the "initiative" required to make a judgement call.