p1_simpson_index outcome

[maja-nagler]

Hi,
I am writing to clarify, in what format do You expect p1_simpson_index function to return the Simpson index value in the first demo. The description in the Project 1 suggests that the expected value of Simpson index is:

That can be visualised by:

Which in various sources is defined as D2 (or dominance index):

https://search.r-project.org/CRAN/refmans/abdiv/html/simpson.html
https://en.wikipedia.org/wiki/Diversity_index (not saying Wikipedia got it correct)

However according to the second practical and mentioned sources Simpson Index is either 1/D2 (by some source defined as Inversed Simpson Index) or 1-D2:

There is no other mention of the Simpson Index in the first project apart from the one below, which is why I am asking this question.

Are we supposed, according to script return D2 (knowing that it is inconsistent with the following projects), 1-D2 or 1/D2?

I would appreciate clarification, especially in case I was getting it wrong.

Kind regards

[mhuzzell]

I'm not sure it's necessarily inconsistent with the following projects, as it's sort of arbitrary what the actual values are. I've just been calculating the Simpson index as instructed (whereby smaller values = more biodiversity) and making notes where relevant that the Simpson index is usually presented as 1 minus that value.

[mhuzzell]

Also worth noting that "how likely two randomly chosen individuals are to be from the same species" does correspond with what you'd expect from an index where smaller = more diverse.

[maja-nagler]

I agree. By consistency I mean phrases like "Run the three functions on the populations provided and check that your results are identical to the original functions" in the following projects (for this, the formula would need to be the same) and the issues of aesthetics, or pedantry associated with marking (I would want to be sure that I won't be marked down on this).

[richardreeve]

The simpson index I'm asking you to calculate throughout is the one I describe in the first project - "the species proportions from the counts (so the total sums to 1), squares them all individually, and add them all together". D2 is 1/Simpson index - The special function is the simpson index, the general function is (well, includes) D2. The "1 minus x" function is nothing I mention in the exercises and nothing I'm interested in.