At 09:09 04/02/01 -0500, Paul Jeffries wrote:
>But isn't it possible to have a scale that has a true zero point but on
>which equal intervals do not always represent the same magnitude of the
>property? Income measured in dollars has a true zero point; zero dollars
>is the absence of income. Yet, an increase in income from say 18,000 to
>19,000 is not the same as an increase in 1,000,000 to 1,001,000. At the
>low end of the income scale an increase of a thousand dollars is a greater
>increase in income than a thousand dollar increase at the high end of the
>scale.
My reaction to this would be that three different measures are being
discussed here.
a) Gross income in dollars. For this measure, the difference between $18000
and $19000 dollars and $1000000 and $1001000 is the same. It is $1000
dollars, and will buy whatever $1000 dollars will buy. If donated to a
beggar on a street corner, it is of the same value whether given by someone
who earns $18000 or $1000000.
b) Net income in dollars. If higher earners pay a higher rate in tax, $1000
dollars difference in gross income leads to different differences for net
income. But if the scale is net income rather than gross income, $1000
dollars' difference means the same at either income level.
c) Satisfaction from income. A graph of this against income would not be
linear. Its gradient would decrease as income increases. (Or even become
negative, in which case it would be difficult to use income to measure
satisfaction at all.) The ratio measure, income, is being used to give an
indication of the underlying variable, satisfaction, but is not a ratio
measure of this.
Jo Tomalin
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