Adjusted metric explainer

The new metric will account for annual global changes in the Nature Index corpus.

17 April 2018

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Annual vacillations in the productivity of journals included in the Nature Index have the potential to slightly skew time-based analyses of national and institutional output. To address this, we have introduced a new qualifier to account for the ups and downs. Below is an explanation, in several graphics, of how this ‘adjusted’ metric is calculated.

The number of primary research papers archived in the Nature Index has wavered over the years — rising to a 2014 peak, and rolling to a 2017 trough. Overall, global production of high-quality research shrank by 2.85% during the six-year period.

Countries and institutions have followed different trajectories. Article counts in the United States and Japan, for example, have consistently declined over the past six years. Meanwhile, China and Germany's output have followed an inverse path of growth.

But these national and institutional changes do not account for the global context. Take the US. Its production of high-quality research papers declined from 27,441 in 2012 to 25,537 in 2017, a 6.94% descent. But remember that global output also shifted down by 2.85% during the same period, which could explain some of the US slump. Adjusting for these fluctuations offers a more representative picture of a country's or institution’s output over time.

To do this, we set the baseline year at 2014 (it could have been any year), and measured the global year-on-year variation to this fixed number. Global output in 2012 was 2.2% less than in 2014, whereas output in 2017 was almost 5% off the mark. We then recalculated country and institutional output to account for these global fluctuations.

The effect is slight. The adjusted trendline slightly aggravates the US decline in article counts prior to 2014, given that it occurred during a period of global growth. In the years after 2014, however, US output stabilizes after accounting for global losses.

The adjusted metric can be applied to article counts (AC), weighted fractional counts (WFC) and fractional counts (FC). It is calculated by multiplying a country's or institution’s annual output in year x — AC, WFC, or FC — by the ratio of the baseline output in 2014 to the global output for year x.

The adjusted metric offers a more nuanced perspective to time-series analyses, and will be a valuable addition to our measurement toolbox.

Data analysis by Aaron Ballagh and Bo Wu.