Timeline for What is covariance in plain language?
Current License: CC BY-SA 3.0
12 events
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| Nov 19, 2020 at 2:35 | comment | added | John D | > In what practical situation can you obtain a covariance without also being able to obtain a good estimate of the scale of the variables? In my discrete math homework lol | |
| Nov 6, 2019 at 22:02 | comment | added | mrgloom |
What is population covariance? Is there any other types of covariance?
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| Mar 2, 2014 at 14:00 | comment | added | Akavall | @loganecolss, sample covariance would indeed be 3, but I am looking at population covariance. | |
| Mar 2, 2014 at 11:37 | comment | added | avocado |
+1, but isn't the cov(x,y)=3?
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| Aug 29, 2012 at 16:26 | comment | added | Michael R. Chernick | @DavidHefferman I think the answer to your question is none. To get a covariance estimate you need the paired data. If you have the paired data you have the individual components and can estimate their scale (e.g. standard deviation). Jeromy Anglim makes a very good point about interpreting in the original units (e.g. dollars in his case). But to make a judegement about a $10,000 change requires some idea of what constitutes a large difference. | |
| Jun 4, 2012 at 1:39 | comment | added | Jeromy Anglim | However, it is not always necessary to know the standard deviation to understand the scale of a variable and thus the strength of a relationship. Unstandardised effects are often informative. E.g., if doing a training course causes people to on average increase there income by $10,000 per year, that's probably a better indication of strength of effect, than saying that there was a r=.34 correlation between doing the course and income. | |
| Jun 3, 2012 at 20:06 | comment | added | Emre | Just say it's a "scale-free measure". | |
| Jun 3, 2012 at 18:45 | comment | added | David Heffernan | In what practical situation can you obtain a covariance without also being able to obtain a good estimate of the scale of the variables? | |
| Jun 3, 2012 at 16:51 | comment | added | Macro | @DavidHeffernan, I think what Akavall is saying is that if you don't know the scale of the variables then covariance does not tell you anything about the strength of the relationship - only the sign can be interpreted. | |
| Jun 3, 2012 at 16:48 | comment | added | Akavall | @DavidHeffernan, yes if scaled by standard deviations then covariance tells us about the strength of the relationship. However, covariance measure by it self doesn't tell us that. | |
| Jun 3, 2012 at 15:35 | comment | added | David Heffernan | "Covariance doesn't really tell you about the strength of the relationship between the two variables, while correlation does." That statement is completely false. The two measures are identical modulo scaling by the two standard deviations. | |
| Jun 3, 2012 at 14:17 | history | answered | Akavall | CC BY-SA 3.0 |