I was explaining my dissertation to a friend the other day, and I came up with this analogy.
Think of the last time you bought something online for yourself. Now pretend the item was a pair of shoes, you bought them from Amazon, and they were the #1 best selling shoe in the world. Next, pretend you bought the pair of shoes because your feet were sore. And pretend your feet were sore because your shoes were a year-old.
The fact your feet were sore because your shoes were old was why you bought shoes. But this didn't determine which shoes you bought. You like particular colors, designs, and fashions. Maybe you want the shoes for walking, or for hiking, or for running. And before you bought the shoes, you likely read the reviews of other shoes, and maybe you called and asked a friend who bought the same shoes a month ago.
The fact that you bought the shoes, and the fact that you were one of many who did so, is diffusion.
If you were a policymaker instead of an Amazon customer, and if your decisions regarded public policy instead of shoes, this would be called policy diffusion.
The fact that you researched which shoes to buy by reading the reviews of others, or by asking a friend, is learning.
If you were a policymaker who drew lessons from the policy experiences of other policymakers, it would be policy learning.
My dissertation looks at policy learning and diffusion. The major difference, however, is that I'm focused on offshore wind energy, far rarer than the #1 best selling shoes on Amazon. By exploring learning and diffusion in the context of Cape Wind, I'm one of the first to look at learning and diffusion when something is new and innovative.
Why is this important? Because the world is becoming increasingly complex, and there are often few models to learn from. Decisions must be made amidst great uncertainty.
It is like living in a world with few, if any, customer reviews.
Except it's public policy, which is a lot more difficult to return.