1) It is a published research, therefore contacting the author would be recommended first.
2) It looks a very old research, so authors might not be in reach. In that case, contacting the journal would be better.
3) As it is a very popular method and over 3000 research have cited it, referring to one of the article for how they used it, can be an option.
4) Last, and might be most relevant, as it is already well established and popular/published method, you dont need any special permission to use it provided you are giving proper references.