I settled on a system for quantifying and naming the difficulty level of my adventure modules. A weakness is that it accounts for monster difficulty, but not environmental hazards and sandbox playstyle, but I think it gives a fairly accurate snapshot for prospecting Game Masters.
Since Labyrinth Lord lays out information to 20 levels in the main book, I created three broad categories:
Low-Level Adventure: Levels 1-6
Mid-Level Adventure: Levels 7-14
High-Level Adventure: Levels 15-20
To determine which category from the three above, calculate the average monster HD in the adventure. Then add and subtract the standard deviation from the HD average to create a level range.
Step 1: Average the HD for all of the monster/encounters in the adventure.
Step 2: Calculate the standard deviation for the HD of all of the monsters/encounters in the adventure.
Step 3: The level range is created by adding and subtracting the standard deviation rounded to the nearest whole number to the average (from step 1).
For example, in my upcoming adventure, Menagerie of the Ice Lord, there are 29 monsters with a total of 76 HD, giving an average of 2.6... which I round to 3. The same data set has a standard deviation of 1.5678... which I round to 2. Therefore, the recomended level range is 1-5 (3-2 and 3+2). The final subtitle for the adventure, therefore, is:
A Low-Level Fantasy Adventure for Character Levels 1-5