http://healthyinfluence.com/wordpress/steves-primer-of-practical-persuasion-3-0/intro/windowpane/

"The point of this demonstration is to show that you can think with numbers in a practical and efficient way without having a statistician in the room.  Anyone can handle the windowpane approach with numbers.  Just have a clear definition of Changed? (Yes or No) and a clear definition of the Group (Treatment or Control).  Then just count and look for percentage differences.  A 10% difference is small, 30% is moderate, and 50% is large.  And, realize that while “small” may be hard to detect, it can definitely make big practical effect.

Now whether you conceptualize Effect Sizes as windowpanes or jars with marbles, you now understand what the idea, Difference, means.  You can count or see No, Small, Medium, or Large Differences and interpret those complex statistical arguments you encounter all the time.  Realize again, that this approach is not Statistics for Dummies, Idiots, or Fools, but is a standard and mathematically correct way to present quantitative information."

http://www.psychologicalscience.org/journals/pspi/pspi_8_2_article.pdf

tldr; Natural frequencies (ratios of counts of subjects) rather than Conditional probabilities, are easier for people to comprehend.