Wednesday, 21 December 2016

Equalised Mean-based Normalised Proportion Cited

The Equalised Mean-based Normalised Proportion Cited (EMNPC) is an indicator to assess the proportion of documents cited (i.e., with a non-zero citation count) to see whether it is above or below the world average or the values for another group. It is designed for web indicators for which a high proportion is uncited so that average citation indicators, such as MNLCS, are not very accurate. It is particularly suitable for metrics designed by Kayvan Kousha, such as Wikipedia citation counts, and syllabus mentions.

EMNPC has a simple formula. For each field f in which group g publishes, calculate the proportion of articles with at least one citation, pgf. Now for the same set of fields, calculate the proportion of articles published by the world with at least one citation, pwf. Now sum the first set and divide by the sum of the second set to get EMNPC for the group.
If this has a value greater than 1 then a higher proportion of articles by group g is cited than average for the world, so g's research has above average impact in terms of the proportion cited. Note that this calculation is unfair if the group publishes small numbers of articles in some fields because all fields have equal weight in the above formula. Small fields should therefore be removed. 

This calculation also gives a higher implicit weight to fields with a relatively high proportion cited because these can dominate the numerator and denominator of the formula, but this is necessary to get narrower confidence intervals (in contrast to the similar MNPC indicator).

Here is a worked example in Excel, showing the formulae used (click to expand).

Confidence intervals

Confidence intervals can be calculated with the formula below.

Here is a worked example in Excel (click to expand).

Spreadsheet and original publication

Download a spreadsheet containing the EMNPC calculations. This also has MNPC calculations, and a second worksheet repeating the calculations with a continuity correction for greater accuracy.

Additional details can be found in this article.
Thelwall, M. (in press). Three practical field normalised alternative indicator formulae for research evaluation Journal of Informetrics. 10.1016/j.joi.2016.12.002


No comments:

Post a comment