Metrics are easy to measure. You can measure avg. time on site. You can measure the number of members. You can measure inbound links. You can even measure number of posts per member.
And if this is what you're measuring, this is what you will get. But it doesn't mean anything. Any rush to a metric quantity is at the expense of a real life quality.
My advice, don't be rigid with measurements. Measure the outcomes of the community. What has changed? What's different now? Who has benefited? Leave room to measure amazing things.
Angela Connor’s community saved a member from eviction. They are a close group. Upon hearing a friend was in trouble they pooled their money and stopped her from being eviected.
That was never part of the plan.
It certainly wasn't in Angela's job description. At no point in her job interview, her brief, her proposal or strategy was there a line that read "stop members from being evicted".
But now, one of Angela's proudest achievements (and certainly her community's finest moment) isn't something most companies would bother to measure.