Here is a 4th method (method 1d) I call the "Learning Tree."
Before getting started, figure out the single most important thing you would like audiences to learn from your talk (Learning Objective 1.0). This should be a qualitative conclusion. Then figure out the next level of ideas that will give them a deeper understanding of that first major learning objective (2a, 2b, 2c, etc.). Keep going until you've figured out all the key points you hope the audience will learn from your talk. You can now make slides to convey those main ideas.
Below is an example from a talk I recently heard, which unfortunately was cluttered with many more objectives than shown on this Learning Tree
The main point the speaker was trying to make is that not all cells in a tumor are lethal, but that there is a subset of "cancer stem cells" that are important for the future course of the disease. Most of the tumor contains cells that are less virulent. As a result we need to develop therapeutics that specifically target these cells.
A second level point he wanted to make is that he could distinguish cancer stem cells from other cells in the tumor by measuring the expression of two surface makers, XX and YY. High XX and Low YY was a characteristic on non-stem cells, low XX and high YY of stem cells. He also wanted the audience to learn that only 1/300 cells in triple negative breast tumors were cancer stem cells and that the research in other tumor types had not been done yet (3rd level under cancer stem cells branch).
On the non-stem cell side (left had side of third level) he wanted the audience to understand that as XX expression moved lower (low-low) the cell was more likely to be permanently in the non stem cell state (not plastic). Conversely as expression of YY rose (high-high), then it became possible for the cell to revert to a stem cell state.
Finally on the lowest level of the tree, he wanted the audience to learn that in the high-high case a somewhat lower expression of X (mid-high) might result in spontaneous transformation of the cell into a stem cell state. Howeverconversion would only occur in high-high cells when they were fed with a magical cocktail called ZZ.
Now the actual presentation can give real data, quantify all these qualitative conclusions, and give more precise quantitative definitions of high-high, high-mid, etc. But the key is to understand qualitatively what you want the audience to learn before you begin making slides. Use the tree to focus your slides on the evidence that support these conclusions. Avoid bringing in other issues that are less important. Make sure the audience learns the point on the tree, no more and no less.
