Epistemic Uncertainty
Epistemic Uncertainty
[Two panels are shown with labels above them.] Regular Uncertainty Epistemic Uncertainty
[In both panels Megan stands in front of a data presentation on a slide behind her. She is pointing at the slide with a stick.]
[In the left panel titled 'Regular Uncertainty'. Megan standing in front of a presentation of a graph showing, from top to bottom, the number 74%, a horizontal line with a small black diamond near the middle representing an average with error bars, and a line of dots representing data in a horizontal scatter plot.] Megan: Our study found the drug was 74% effective, with a confidence interval from 63% to 81%. 74%
[In the right panel titled 'Epistemic Uncertainty'. Megan stands in front of a presentation of data with a silhouette of a man with a hat labelled with a white question mark. Above this are three guesses of the "real" result and its relation to the study result.] Megan: Our study found the drug to be 74% effective. Megan: However, there is a 1 in 4 chance that our study was modified by George the Data Tamperer, whose whims are unpredictable. 73 -> 74?? 47 -> 74?? 0 -> 74?? ?

This comic is a comparison of two different research studies. One of these studies shows "regular uncertainty". One of these studies shows "epistemic uncertainty." In both panels, the core data is the same. The drug in question is 74% effective. However, the uncertainty qualities are different. The first is straightforward. The confidence interval (the error bars on the chart) is from 63 to 81%. The second panel includes the additional wrinkle of "George the Data Tamperer, whose whims are unpredictable."
In statistics, a confidence interval is an estimate which provides a range of values. These values are based on the statistical probability that the data collected represents a certain result. The confidence interval is a reflection on the uncertainty imposed by the limits of study sample sizes. No study will ever have an infinite data set. [ citation needed ] As a result, it is possible for different studies to give slightly different results.  Averaging the results of multiple studies can give a result that is probably more accurate. The result given may still be skewed. A small skew is more probable than a large one, though. For example, if a drug was 80% effective it would be possible for several small studies to show a spread of different results with an average of 74% effectiveness. If the drug was 99% effective it would still be possible to randomly end up with the same data. However, this would be highly unlikely. This gives us a spread of "likely" predictions. Predictions outside a certain interval are considered too unlikely to be realistic.
George the Tamperer and Evangeline the Adulterator (from the title text) are analogous to the characters from Alice and Bob cryptography thought experiments. In the most basic examples, Alice and Bob are communicating. A third party, Eve the Eavesdropper, is spying on them. Both George and Evangeline have the ability to alter the study's results. George and Evangeline add uncertainty to the final data product. Specifically, they add epistemic uncertainty.
Epistemology – unlike epidemiology – is the branch of philosophy related to knowledge. Thus epistemic uncertainty is the ultimate impossibility to be sure that what we know is accurate. We are not unsure what is accurate beause of failures in measurement. We are unsure what is accurate because of the intrinsic limits of knowledge. It seems that the "epistemic uncertainty" data has a 25% chance of data tampering by George. In  the previous study, the data is known but its reflection of the general case is uncertain to an extent. In contrast, in this study even the knowledge of whether any single data point is correct is uncertain. Thus, their data has a 25% chance of being incorrect. There is no possible statement about how incorrect it may be.
The title text mentions an individual called "Evangeline the Adulterator." She adulterates their drug doses. If this happened, the researchers would not even be sure the patients received the dosages (or exacting medicines/placebos) as prescribed. The study methodology itself would be in doubt.
[Two panels are shown with labels above them.] Regular Uncertainty Epistemic Uncertainty
[In both panels Megan stands in front of a data presentation on a slide behind her. She is pointing at the slide with a stick.]
[In the left panel titled 'Regular Uncertainty'. Megan standing in front of a presentation of a graph showing, from top to bottom, the number 74%, a horizontal line with a small black diamond near the middle representing an average with error bars, and a line of dots representing data in a horizontal scatter plot.] Megan: Our study found the drug was 74% effective, with a confidence interval from 63% to 81%. 74%
[In the right panel titled 'Epistemic Uncertainty'. Megan stands in front of a presentation of data with a silhouette of a man with a hat labelled with a white question mark. Above this are three guesses of the "real" result and its relation to the study result.] Megan: Our study found the drug to be 74% effective. Megan: However, there is a 1 in 4 chance that our study was modified by George the Data Tamperer, whose whims are unpredictable. 73 -> 74?? 47 -> 74?? 0 -> 74?? ?
