Q:

How to measure the value of Product management?

There are 2 types of product management broadly - New Product and Existing products. For an existing product, the task of the product manager is to increase revenue, in a declining market share scenario arrest/protect the revenue from further decline. Find ways for cost reduction.
Is there a way to collectively look at the performance of the PM by looking at the aforementioned indicators and other metrics and condense them into a single composite variable or index of sorts.
Such that when one looks at the number, depending on the magnitude one can say the PM has done his job well, moderately well, or has performed poorly.

A:

There are many ways to define the value added to a product. These include:

Revenue generated
Cost savings
Cost of not doing the work (e.g. if we don't do this work a security breach is possible that would damage the organisation)
Helps to reach the organisation's objectives (e.g. helps to extend market share, helps to enter a new market, helps patients, etc.)
Regulatory
Compliance

Each organisation will have their own definition of value that may be a combination of the factors listed above.
One metric might be the value (as defined by the organisation) added to the product over time. However Product Management does not work in isolation. A better metric would measure the overall effectiveness of the product team that includes both the Product Management and the Delivery Team.
I can imagine a metric for a product team might be: value added divided by the the cost of the team.

