What statistic to use to assess repeatability of measurement I want to assess the repeatability of a measurement device. Let's say I have made three measurement with the same device under the same conditions. What statistic is useful for assessing the repeatability for such a case. An example of the measurement is shown in the plot below. 

 A: It's not 100% clear what you mean by repeatability. But, in medicine, health services research, and psychology, we often want to know the correlation of repeated measures on the same person taken within a short time frame. For example, say I administered a depression symptom score to a group of people, and then I administered the same questionnaire two weeks later. I am expecting the correlation between the two scores to be high, like over 0.6 (which I think is what the real-life test reliability of the PHQ-9 or a similar score has been reported as). That is actually going to be low in many contexts, but depressive symptoms could fluctuate over two weeks. In our case, we can't really just repeat the test right afterward - people could remember and just regurgitate their answers. If you are taking someone's blood pressure, you will be able to measure at shorter intervals.
In your case, if you calculated the intra-class correlation among your 3 measures, that would assess the test-retest reliability of whatever it is you measured. I am assuming you measured them at the same time on the same people.
