Probably the single biggest challenge in setting performance objectives is making them measurable.
This is important because …
Human beings adjust behavior based on the metrics they’re held against. Anything you measure will impel a person to optimize his score on that metric. What you measure is what you’ll get
Dan Ariely article “You are what you measure” in Harvard Business Review
And if we get it wrong, it can be dangerous and lead to the measure having an ineffective, or damaging, impact …
It[‘]s really easy to decide to measure something … and screw up a team beyond belief. For example, if I measure how productive individual programmers are, then it[‘]s to the advantage of individuals to focus on their own work and spend less (or no!) time helping others. Completely kills teamwork
Brian Button (Agile programmer and blogger) in “‘You get what you measure’ versus ‘what you measure you can manage'” – article no longer accessible)
So it’s worth getting it right … but it’s not so simple …
The most important things cannot be measured
This is even more true as most things sit within complex systems and have an impact over the long-term and so can’t be easily isolated or measured within a single twelve-month performance appraisal period.
John Tomlinson 