Qualitative economics

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Qualitative economics is the representation and analysis of information about the direction of change (+, -, or 0) in some economic variable(s) as related to change of some other economic variable(s). For the non-zero case, what makes the change qualitative is that its direction but not its magnitude is specified.[1]

Typical exercises of qualitative economics include comparative-static changes studied in microeconomics or macroeconomics and comparative equilibrium-growth states in a macroeconomic growth model. A simple example illustrating qualitative change is from macroeconomics. Let:

GDP = nominal gross domestic product, a measure of national income
M = money supply
T = total taxes.

Monetary theory hypothesizes a positive relationship between GDP the dependent variable and M the independent variable. Equivalent ways to represent such a qualitative relationship between them are as a signed functional relationship and as a signed derivative:

G D P = f ( M + ) {\displaystyle GDP=f({\overset {+}{M}})\quad \\!} or  d f ( M ) d M > 0. {\displaystyle \quad {\frac {df(M)}{dM}}>0.}

where the '+' indexes a positive relationship of GDP to M, that is, as M increases, GDP increases as a result.

Another model of GDP hypothesizes that GDP has a negative relationship to T. This can be represented similarly to the above, with a theoretically appropriate sign change as indicated:

G D P = f ( T − ) {\displaystyle GDP=f({\overset {-}{T}})\quad \\!} or  d f ( T ) d T < 0. {\displaystyle \quad {\frac {df(T)}{dT}}<0.}

That is, as T increases, GDP decreases as a result. A combined model uses both M and T as independent variables. The hypothesized relationships can be equivalently represented as signed functional relationships and signed partial derivatives (suitable for more than one independent variable):

G D P = f ( M + , T − ) {\displaystyle GDP=f({\overset {+}{M}},{\overset {-}{T}})\,\\!\quad } or  ∂ f ( M , T ) ∂ M > 0 , {\displaystyle \quad {\frac {\partial f(M,T)}{\partial M}}>0,\quad } ∂ f ( M , T ) ∂ T < 0. {\displaystyle {\frac {\partial f(M,T)}{\partial T}}<0.}

Qualitative hypotheses occur in earliest history of formal economics but only as to formal economic models from the late 1930s with Hicks's model of general equilibrium in a competitive economy.[2] A classic exposition of qualitative economics is Samuelson, 1947.[3] There Samuelson identifies qualitative restrictions and the hypotheses of maximization and stability of equilibrium as the three fundamental sources of meaningful theorems — hypotheses about empirical data that could conceivably be refuted by empirical data.[1]

## Notes

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1. ^ a b James Quirk, 1987. "qualitative economics," The New Palgrave: A Dictionary of Economics, v. 4, p. 1.
2. ^ J. R. Hicks, 1939. Value and Capital. Oxford.
3. ^ Paul A. Samuelson, 1947. Foundations of Economic Analysis, pp. 5, 21-29.

## References

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* J. R. Hicks, 1939. Value and Capital. Oxford.
* Kelvin Lancaster, 1962. "The Scope of Qualitative Economics," Review of Economic Studies, 29(2), p p. 99-123.
* W.M. Gorman, 1964. "More Scope for Qualitative Economics," Review of Economic Studies, 31(1) p p. 65-68.
* James Quirk, 1987. "qualitative economics," The New Palgrave: A Dictionary of Economics, v. 4, pp. 1–3.
* _____ and Richard Ruppert, 1965. "Qualitative Economics and the Stability of Equilibrium," Review of Economic Studies, 32(4), p p. 311-326.
* Paul A. Samuelson, 1947. Foundations of Economic Analysis, Harvard University Press. ISBN 0-674-31301-1