In today's economic scenario, everyone in my organization is talking about "productivity improvement" but no one has a clue how to measure it. Different people percieve productivity in their own way. As per the metrics definition it is "size of work product/ effort spent", while in my experience I have rarely seen organizations measuring size in Function Points (FP) or Source Lines of Code (SLOC) very accurately. Measuring size itself is a distant reality.
Could you share some of your thoughts or ideas or resources on "improving software productivity" or "measuring developers productivity" in simple terms?
The first thing that you have to do is define what productivity improvement means for your organization. As you have stated, everyone has a different definition. So by asking for help you will receive additional definitions to what you have already encountered in your organization, and these answers may be as unsatisfactory as what you have already discussed internally. Instead I recommend that you hold a meeting with your management team and come to consensus on what productivity means for your organization. What does management care about?
What I am suggesting that you do is perform Measurement and Analysis SP 1.1 Establish and maintain measurement objectives that are derived from identified information needs and objectives.
Again, what is your management concerned about? Do they want to reduce time to market? Do they want to reduce total lifecycle cost? Do they want to improve product quality? etc. The answers to these and similar questions will provide you with the information you need to determine what productivity improvement means for your company.
And if you are still struggling with this concept, I suggest that you hire a CMMI consultant with a Measurement and Analysis background who can help you and your organization define the specific measures you need for your company.