Instrumentation & Measurement Magazine 24-1 - 45

On the Commonly-Used
Incorrect Visual Representation
of Accuracy and Precision
Shervin Shirmohammadi, Luca Mari, and Dario Petri

W

e performed a Google image search using the
search phrase " accuracy and precision " and, after removing unresponsive and duplicate web
pages from the search results, found that 78 of the top 100 results use the bullseye chart to visually explain this concept.
Unfortunately, we also found that 52 of those 78 results, i.e., an
incredible two thirds, use a visual similar to what is shown in
Fig. 1(i) or Fig. 1(ii), both of which are at best highly misleading and factually incorrect according to relevant standards and
guidelines. In this figure, the black dots represent the values
obtained by replicated measurements of the same measurand
(the quantity intended to be measured), and the visual aims
to present how close the measured values are to each other
and to an agreed-upon reference value, represented by the red
bullseye. In the search results, visuals similar to Fig. 1(i) and

Fig. 1(ii) appeared 25 and 27 times, respectively. In the top 20
search results, which is where the great majority of users look
for answers, the earliest correct visual appeared only at position 11, followed by 13, 15, and 19 in the rankings. The great
majority of the 52 incorrect visuals were in non-peer-reviewed
documents, reinforcing the notion that one should not believe
everything one sees on the internet, although shockingly, a
few were in papers published in peer-reviewed scientific venues, including one in Elsevier's Journal of Clinical Epidemiology
and another one in the SCMR's Journal of Cardiovascular Magnetic Resonance, both well-cited journals. The actual numbers
are probably higher, as many scientific articles are behind paywalls and inaccessible to Google search.
There is of course a degree of uncertainty in this search
experiment: repeating the search in a different geographic

Fig. 1. Commonly-used incorrect representations of Accuracy and Precision.
February 2021	

IEEE Instrumentation & Measurement Magazine	45
1094-6969/21/$25.00©2021IEEE



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