588


NOVEMBER 2022


Again, diagnostic sensitivity is a parameter describing qualitative performance of the technique, and there is no relationship with quantitative aspects.


Accuracy and precision


Accuracy and precision are parameters describing the performance of quantitative techniques and are, thus, highly


relevant for evaluating faecal egg count techniques. I emphasise that even though these terms may appear similar at a first glance, they are far from synonymous and should not be used interchangeably. A technique can be accurate without being precise and vice versa. These concepts are illustrated in Fig 1 and will be explained in the following. Accuracy is a measure of how close a given technique measures to the true count. As illustrated in Fig 1, accuracy is


6


True Counts


20


Sample Processing


Observed Counts 1 22 2 3


Low Accuracy High Precision


04 0 0


Low Accuracy Low Precision


57 6 5 6


High Accuracy High Precision


6 11 2 8


High Accuracy Low Precision


4 1 7 9 10 9 9 8


Low Accuracy High Precision


11 4 2


Low Accuracy Low Precision


19 20 21 20 20 5


High Accuracy High Precision


21 22 15 19 24


High Accuracy Low Precision


Fig 1: Illustration of accuracy and precision for manual parasite faecal egg counts. Accuracy is a measure of how close an observed count is to the true count and is determined by the proportion of eggs lost during sample processing and flotation steps. Precision is a measure of how close repeated counts from the same sample are to each other. The figure illustrates these principles for a low (6) and a higher (20) true egg count sample and for four techniques with different combinations of accuracy and precision. A low accuracy means a lower magnitude of egg counts determined, while a low precision means more variation between the five repeated counts in the examples.


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Precision


Accuracy


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