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J Clin Pathol. May 2001; 54(5): 385–390.
PMCID: PMC1731421

Observer accuracy in estimating proportions in images: implications for the semiquantitative assessment of staining reactions and a proposal for a new system


Background—The results of immunohistochemical staining are often assessed by semiquantitative scoring. However, these scoring systems are usually non-standardised and there has been little evaluation of the accuracy and reliability of this subjective assessment.

Aims—To assess the accuracy of observer estimation of proportions of objects in an image.

Methods—Images were generated that contained known proportions of pink squares in grids of 50 x 50 and 100 x 100 squares. Observers were shown each image for five seconds in random order and either estimated the proportion of pink squares or selected the image (from a pair of images) that contained the greater proportion of pink squares. The observers were four consultant histopathologists, seven trainee histopathologists, and six control non-histopathologists.

Results—The raw estimations of proportions showed a close correlation with the real proportions, with correlation coefficients of 0.94 and 0.95 for consultant and trainee histopathologists on the 50 x 50 grids. However, the performance in the comparison task was much higher, with an almost perfect classification for grids of equal size even when the proportions only differed by 5%.

Conclusions—Histopathologists can estimate proportions of objects in an image with a reasonable degree of accuracy in this abstract test system. All observers, whether histopathologists or not, can discriminate between proportions that are only 5% different in equal sized image grids. This suggests that the generation and use of carefully calibrated reference images could greatly improve the accuracy and reliability of semiquantitative scoring of immunohistochemical or any other staining.

Key Words: scoring • immunohistochemistry • semiquantitative • interobserver agreement • κ statistics

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Selected References

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Figures and Tables

An external file that holds a picture, illustration, etc.
Object name is 00176.f1.jpg
Figure 1 Examples of the test images. (A) A 50 x 50 grid in which 40% of the squares are coloured pink. (B) Two 100 x 100 grids in a comparison image; the left hand grid has 50% pink squares, the right hand grid has 45%. Despite the small difference ...
An external file that holds a picture, illustration, etc.
Object name is 00176.f2.jpg
Figure 2 Scattergrams for the estimated proportion of pink squares in a 50 x 50 grid for (A) the consultant histopathologists, (B) the trainee histopathologists, and (C) controls. The regression line and correlation coefficient were derived using the ...
An external file that holds a picture, illustration, etc.
Object name is 00176.f3.jpg
Figure 3 Scattergrams for the estimated proportion of pink squares in a 100 x 100 grid for (A) the consultant histopathologists, (B) the trainee histopathologists, and (C) controls. The regression line and correlation coefficient were derived using the ...

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