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Explaining half the variation, and the other half? The point was to draw a connection for the general audience, not present the most scientifically accurate de

Explaining half the variation, and the other half? The point was to draw a connection for the general audience, not present the most scientifically accurate description of a relationship between two variables -- that's what the links to the research are for.

kristjansson 8y ago
It's good to communicate for a general audience, but your presentation misleads rather than simplifies. > meaning the combined measurement accurately predicts how a potential college applicant will perform in their first year of college 56% of the time. "accurately predicts...56% of the time" implies that half of predictions are 'accurate', which most readers would interpret as 'correct' i.e. knowing SAT + HSGPA allows you to state FYGPA _exactly_ for about half of cases. That's not what the research you cited says. Rather, the square of the multiple correlation R (which is exactly R^2, the coefficient of determination) indicates how much of the variance in the output variable is explained by the input variables. That quantity _must_ be communicated in terms of the strength of the relationship, not accuracy for a given or share of cases as it doesn't tell us anything about a given case. One could say it tells us about 30% (0.56^2, correction from my statement above) of the information we'd need to know to perfectly predict the outcome, or that the relationship is better than random, but doesn't predict perfectly, or ... Additionally, table 5 of the link you cited indicates the adjust correlation coefficient b/w FYGPA and the combination of HSGPA and SAT is 0.62. None of the numbers in that table are 0.56, so I'm not sure where you pulled that exact number from. I've used 0.56/56% above to be clear which quantity I'm referring to.
- ordinaryperson 8y ago
  Uh...this is exactly what I mean. Your description is 100% scientifically accurate but probably way beyond the average reader. Again, if you can simplify this in a way more accurate than I have, great, be my guest-- I look forward to reading it. R^2, coefficient of determination, output variable variance, etc etc -- most readers aren't going to go that deep in the math. For those who do, like you, the links to the actual research is provided. But so far all I see are data scientists complaining about how my description is not 100% statistically accurate without providing any alternative explanation that doesn't devolve into variance of output variables. Again, be my guest to show me I'm wrong, but what you wrote above is not something that would be easy to understand for the general audience, IMHO.
  - kristjansson 8y ago
    The concerning (mis)interpretation of your statement is what I said on the third line above: > "accurately predicts...56% of the time" implies that half of predictions are 'accurate', which most readers would interpret as 'correct' i.e. knowing SAT + HSGPA allows you to state FYGPA _exactly_ for about half of cases. This interpretation is easy to arrive at, and clearly does not correspond to a reasonable understanding of the source, even for a general audience. I provide two suggestions above: > One could say it tells us about 30% of the information we'd need to know to perfectly predict the outcome, or that the relationship is better than random, but doesn't predict perfectly
    - ordinaryperson 8y ago
      OK, but that only makes it more confusing. You say it tells us about 30% of the information we'd need to know...which makes it sound (to the lay person) like there's no connection because 70% of the information is elsewhere! I appreciate your commitment to academic rigor but sometimes oversimplifying things, even at the cost of mathematical accuracy, is enough for a general audience who aren't going to compute variance of output variables.
      - kristjansson 8y ago
        This isn't about academic or mathematical rigor - this is about responsible communication of statistics. You're right that a general audience isn't going to look at the source, nor think about variance of output variables. Therefore, it's the responsibility of us as communicators of statistics to relate the conclusions that can be drawn from the data in a way that first and foremost is not wrong or misleading, and secondly captures the concept as accurately as possible for the audience. The first principle is the overriding obligation. Your simplification can capture as little of the information and conclusions supported by the data as you want, but it cannot imply or state conclusions that are not supported. You're getting this response to your statement, from me and others, because your interpretation of the source can easily be read as drastically overstating the character (and strength) of the relationship supported by the data - even if that's not what you intended.
jamesmather 8y ago
>A better summary would be that those two quantities explain about half of the variation, not that they predict accurately half the time. Frankly this is not correct either, that would be right if we were talking about a coefficient of determination aka R^2 but we are not. we are talking about correlation coefficients which are totally different. >Explaining half the variation, and the other half? In the context of coefficients of determination(WHICH ARE NOT RELEVANT IN THIS CASE) this would mean that those variables explains 50% of the variance and the other 50% is either unexplained or explained by other variables. >If you have a better description, it's more helpful to chime in with that instead of "You're wrong!" >the combined measurement accurately predicts how a potential college applicant will perform in their first year of college 56% of the time Your statement was indeed totally wrong and honestly the lack of statistical understanding in this thread, among all participants, is a little disturbing. Correlation coefficients imply just that, correlation. Nothing more, your "simplification" was totally incorrect and makes implications which are in no way supported by the data. Your own citation explains correlation quite clearly - "A correlation indicates the extent to which variables are linearly related and can range from –1.0 to 1.0 (Miles and Shevlin, 2001). A correlation of 1.0, for example, indicates a perfect positive linear relationship. A general rule of thumb for interpreting correlation coefficients is offered by Cohen (1988): a small correlation has an absolute value of approximately 0.1; a medium correlation has an absolute value of approximately 0.3; and a large correlation has an absolute value of approximately 0.5 or higher" Theres no way to simplify this as correlation is already one of the simplest concepts in statistics...

kristjansson 8y ago

It's good to communicate for a general audience, but your presentation misleads rather than simplifies. > meaning the combined measurement accurately predicts how a potential college applicant will perform in their first year of college 56% of the time. "accurately predicts...56% of the time" implies that half of predictions are 'accurate', which most readers would interpret as 'correct' i.e. knowing SAT + HSGPA allows you to state FYGPA _exactly_ for about half of cases. That's not what the research you cited says. Rather, the square of the multiple correlation R (which is exactly R^2, the coefficient of determination) indicates how much of the variance in the output variable is explained by the input variables. That quantity _must_ be communicated in terms of the strength of the relationship, not accuracy for a given or share of cases as it doesn't tell us anything about a given case. One could say it tells us about 30% (0.56^2, correction from my statement above) of the information we'd need to know to perfectly predict the outcome, or that the relationship is better than random, but doesn't predict perfectly, or ... Additionally, table 5 of the link you cited indicates the adjust correlation coefficient b/w FYGPA and the combination of HSGPA and SAT is 0.62. None of the numbers in that table are 0.56, so I'm not sure where you pulled that exact number from. I've used 0.56/56% above to be clear which quantity I'm referring to.

ordinaryperson 8y ago
Uh...this is exactly what I mean. Your description is 100% scientifically accurate but probably way beyond the average reader. Again, if you can simplify this in a way more accurate than I have, great, be my guest-- I look forward to reading it. R^2, coefficient of determination, output variable variance, etc etc -- most readers aren't going to go that deep in the math. For those who do, like you, the links to the actual research is provided. But so far all I see are data scientists complaining about how my description is not 100% statistically accurate without providing any alternative explanation that doesn't devolve into variance of output variables. Again, be my guest to show me I'm wrong, but what you wrote above is not something that would be easy to understand for the general audience, IMHO.
- kristjansson 8y ago
  The concerning (mis)interpretation of your statement is what I said on the third line above: > "accurately predicts...56% of the time" implies that half of predictions are 'accurate', which most readers would interpret as 'correct' i.e. knowing SAT + HSGPA allows you to state FYGPA _exactly_ for about half of cases. This interpretation is easy to arrive at, and clearly does not correspond to a reasonable understanding of the source, even for a general audience. I provide two suggestions above: > One could say it tells us about 30% of the information we'd need to know to perfectly predict the outcome, or that the relationship is better than random, but doesn't predict perfectly
  - ordinaryperson 8y ago
    OK, but that only makes it more confusing. You say it tells us about 30% of the information we'd need to know...which makes it sound (to the lay person) like there's no connection because 70% of the information is elsewhere! I appreciate your commitment to academic rigor but sometimes oversimplifying things, even at the cost of mathematical accuracy, is enough for a general audience who aren't going to compute variance of output variables.
    - kristjansson 8y ago
      This isn't about academic or mathematical rigor - this is about responsible communication of statistics. You're right that a general audience isn't going to look at the source, nor think about variance of output variables. Therefore, it's the responsibility of us as communicators of statistics to relate the conclusions that can be drawn from the data in a way that first and foremost is not wrong or misleading, and secondly captures the concept as accurately as possible for the audience. The first principle is the overriding obligation. Your simplification can capture as little of the information and conclusions supported by the data as you want, but it cannot imply or state conclusions that are not supported. You're getting this response to your statement, from me and others, because your interpretation of the source can easily be read as drastically overstating the character (and strength) of the relationship supported by the data - even if that's not what you intended.

jamesmather 8y ago

>A better summary would be that those two quantities explain about half of the variation, not that they predict accurately half the time. Frankly this is not correct either, that would be right if we were talking about a coefficient of determination aka R^2 but we are not. we are talking about correlation coefficients which are totally different. >Explaining half the variation, and the other half? In the context of coefficients of determination(WHICH ARE NOT RELEVANT IN THIS CASE) this would mean that those variables explains 50% of the variance and the other 50% is either unexplained or explained by other variables. >If you have a better description, it's more helpful to chime in with that instead of "You're wrong!" >the combined measurement accurately predicts how a potential college applicant will perform in their first year of college 56% of the time Your statement was indeed totally wrong and honestly the lack of statistical understanding in this thread, among all participants, is a little disturbing. Correlation coefficients imply just that, correlation. Nothing more, your "simplification" was totally incorrect and makes implications which are in no way supported by the data. Your own citation explains correlation quite clearly - "A correlation indicates the extent to which variables are linearly related and can range from –1.0 to 1.0 (Miles and Shevlin, 2001). A correlation of 1.0, for example, indicates a perfect positive linear relationship. A general rule of thumb for interpreting correlation coefficients is offered by Cohen (1988): a small correlation has an absolute value of approximately 0.1; a medium correlation has an absolute value of approximately 0.3; and a large correlation has an absolute value of approximately 0.5 or higher" Theres no way to simplify this as correlation is already one of the simplest concepts in statistics...