Want to measure the effectiveness of a design? Focus on the scale of impact.
The challenge with trying to determine the impact of a design solution in the private and public sector is that it is hard to quantify. People can't seem to figure out whether or not design makes a difference, particularly when what they really want is simply action.
Scale of impact is the consideration of how a design solution can affect all parts of a business or government ecosystem. One needs to understand how a decision will affect people at every jump in scale from the individual to the larger organization to the industry and then back down to the individual.
Where do you start?
Start with examining the big picture. What overall goal do you want to achieve? With this is mind, think about how your design will impact the local user, or a single individual. How will it impact a small group of users; a community of users; and then people not in your community?
Shifting from the micro to the macro perspective and comparing and contrasting what you see will give you a deeper sense of how your design solution may actually work and whether or not it is consistent with your vision for your organization. When an idea is developed for a small scale application, and then pulled out of that environment and placed in a new, larger context, the inefficiencies are generally very clear.
A design solution should work well at both small and large scales to be truly effective. Once you get over this hurdle, scaling up a small idea to solve a systemic problem is much easier to accomplish.