Yes, there are notable differences. Often, people misinterpret or mistakenly use them interchangeably.
However, the differences can be explained in three succinct ways.
Intent
Effectiveness: Doing the right thing.
Efficiency: Doing things right.
Manner
Effectiveness: Focuses on what purpose is being achieved; Goal. The Big Picture.
Efficiency: Focuses on how the purpose is achieved; Performance. The Extent.
Time and Effort
Effectiveness: Little attention to time, effort and cost.
Efficiency: Strongly considers time, effort and cost.
For example,
I could use a thousand words to explain the differences between effectiveness and efficiency. If you got the point, then I'm effective. Since I pursued the right goal. But if I had explained it with less than a hundred words, and you're still able to clearly understand it, then I'm efficient and effective. Since I was time conscious and it cost me less words, yet I pursued the right goal.
Or
Imagine a company becoming too focused on minimizing cost by producing more products in short periods of time and making lots of money. This company is efficient. But the moment their products start losing the quality they once had, because of their undue focus on quantity and profit, they would lose their overall effectiveness and values. In the long run, lose customers, by pursuing the wrong combination of goals.
The bottom line is, you can have your heart in the right place (effective); pursue the right goals, but be inefficient in achieving them.
You can also become too focused on efficiently using or maximizing limited resources, to the point of losing the right goals, values and overall effectiveness in the process.
If you could only be either effective or efficient, which would you choose?
I will choose to be effective. I'd rather have my heart in the right place. I cannot trade my values for efficiency.
Efficiency is merely a sub task of effectiveness. You lose sight of the big picture when you focus on efficiency.
With that said, a combination of both would make a perfect mix. Effectiveness and efficiency are both invariably important in life and in a business, in order to be successful and attain maximum satisfaction. But if one must be forgone, I would suggest efficiency should be neglected.
Too often in the world we live in, people choose to be efficient rather than being effective. People would do anything to get what they want, within the quickest time possible. I'm not saying it's wrong to try and get what you want as fast as possible. What I'm saying is; is it worth losing yourself, your values and ethics?
If your choices or decisions would cost you your values. Then, it isn't right for you. Integrity should be your most valuable asset. What shall it profit a man that he gains the world but loses himself?
Be yourself and don't let anything take that away from you, not even you.