Non the less you could have a go. You must have taken part in decisions or taken part in activities, duties, etc., which were a part of some larger initiative. Cost benefits may not have been an obvious issue, but regardless of whether they were or not, there is a cost bv benefit in almost all management activities. Idf you can't think of anything at work then invent some theoretical scenario and cost it out.

A nice simple one is replacing a member of staff.

Whilst you are missing this staff member what are the losses? Real, actual or simply guessed at ??
How much did it - or would cost to hire someone new - adverts, management time involved and so on.
How long (and how much effort/cost) was it before the new starter got up to speed?

And so on. Just remember this isn't an accurate calculation and is often based on guesswork and assumptions.

Hi Charlie. Examples of ROI could be savings on temporary staff costs as a result of reducing sickness absence; investing time in managing absence delivers a return. Or investing in development of staff could reduce turnover delivering savings and increase in quality. I will often look at performance against KPIs to demonstrate that the initiatives or interventions invested in are delivering results. Hope that helps and good luck with the next interview.

In reply to Suzanne:

In a previous role when we did big redundancy exercises, we had to complete a Capital Expenditure Form (honestly!)
The return was generally about 6 months. Not a true ROI type of figure but it makes more sense than a percentage.

Hi Charlie... most public sector orgs will probably have business intelligence units with loads of data; some posts will also be funded from capital grants, rather than the revenue budget.

Charlie, good luck with taking the next step in your career and moving from an Advisor to HRBP role. I imagine your potential employer is wanting to test out your business acumen, to check out your appreciate for the bigger picture and the ability for you to draw lines from the work you are doing to the impact, outcomes and returns it is showing.

This can be tricky in some people projects as not all have a direct, causal relationship however consider examples of the work you have done:
1. What was the overarching purpose of it? - The why?
2.What did you expect to see when the work was complete?
3. How could you measure the results - this can be qualitative as well as quantative and other KPI metrics
4. What was the budget for it and did it come in on budget, over or under and what were your views on this.

There's a lot of focus on evidence based HR and it's worth checking out resources on this on the CIPD and also on cebma.org/.../ or check out and follow Prof Rob Briner, and others, in this field.

Good luck making the move. It's hard when we stumble to remember interview stumblings are great sources of learning.

To add a bit more conversationally...

The way I tend to ask this question to HR bods is not about ROI but after they have waxed lyrically about a pet project I ask the simple question "So what?". That's what the ROI is probably getting towards - the so what question. How did your pet project or proudest achievement make the organisation better and how? Can you quantify it in any way (and many HR people really dont get data well - its the biggest gap in our profession IMO).

Everyone now completes our super appraisal form - so what? etc etc