I did a similar analysis a few months ago, which was focused more on general distinctions between keywords within a topic. This analysis is much more focused on the types of variations of keywords that we are seeing being grouped. These types of variations were categorised by, among others, Jennifer Slegg at The SEM Post.

The five types of variations that I’ve looked into for this analysis are the following:

Plurals. For example, [waffle maker] and [waffle makers]

Verb stems with and without suffixes. For Primary Metal Manufacturers Email List example, [calculate], [calculated] and [calculating].
Keywords with and without punctuation. For example, [midnight’s children] and [midnights children]
Keywords with and without typos. For example, [heart rate monitor] and [heart rat monitor].
For each of these five categories, I put together a list of 50-100 keywords, along with a variation for each. Within these keyword pairs I investigated whether or not Keyword Planner reported the same volume, and also used the rank tracking tool STAT to see what pages are ranking for each keyword.

From that analysis

I was able to measure the prevalence of DW Leads grouping keyword volumes within each category (i.e. the percentage of keyword pairs that have grouped volumes), and the similarity of the SERPs (the number of top ten results that were shared between the two keywords) for grouped and ungrouped keyword pairs.