Normalization of rare citation events in the context of uptake of research in the non-scientific literature

The citation uptake of research papers in the non-scientific literature is often sparse. It is thus frequently reported as a proportion of cited papers instead of as an average of the papers’ citation counts. Citation-based indicators are commonly normalized by dividing a paper’s citation count (or binary score; 0 = not cited, 1 = cited) by the world average (or proportion) in the corresponding year, field and document type. Such ratio-based method can generate outliers when dealing with the binary scores. At low aggregation levels, these outliers can produce unreliable results. Here, a ratio-based method is compared to one in which the world’s proportion is subtracted from the papers’ scores using a set of universities as units of analysis. This difference-based method has two main advantages: interpretation of results is more transparent/straightforward, and outliers are less problematic, leading to narrower confidence intervals.