I have two dataset: population density and case fatality rate. Population density is measured as number of people living in an area divided by that area size in square miles (number of people/area size). Case fatality rate is calculated as total death from an infection divided by total number of infections (total death/total infection). Are population density and case fatality rate intervals?
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$\begingroup$ Presumably you mean of "interval data type." But could you explain why the answer would be relevant to any kind of data analysis or investigation? $\endgroup$whuber– whuber ♦2022-01-10 21:09:35 +00:00Commented Jan 10, 2022 at 21:09
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1$\begingroup$ Both datasets take only non-negative values. $\endgroup$BruceET– BruceET2022-01-10 22:33:31 +00:00Commented Jan 10, 2022 at 22:33
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$\begingroup$ @whuber yes I meant are they interval data type. I want to find if there is a correlation between them. I use population density as the independent value. $\endgroup$kaka– kaka2022-01-11 21:26:30 +00:00Commented Jan 11, 2022 at 21:26
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$\begingroup$ @BruceET yes. So are they interval data type? $\endgroup$kaka– kaka2022-01-11 21:26:57 +00:00Commented Jan 11, 2022 at 21:26
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2$\begingroup$ For assessing relationships or correlations, it is superfluous to determine the data type. $\endgroup$whuber– whuber ♦2022-01-11 21:42:30 +00:00Commented Jan 11, 2022 at 21:42
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1 Answer
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Both population density and case fatality rate are based on a ratio of a necessarily non-negative value to a necessarily positive value. That's the definition of a ratio-scale measurement.
As comments have pointed out, you don't need to distinguish interval from ratio data types to do correlations.* Also, correlations are generally considered to be symmetric between 2 variables, without a defined "independent" variable. That distinction becomes important when you are doing regression.
*I don't find the "interval" measurement type as defined by Stevens to be very helpful, except to provide a warning about taking ratios. I suspect that most users of this site would lean toward the Mosteller/Tukey typology, perhaps extending it in particular cases with things like cyclic data.
