Table A-11. Measures of Central Tendency and Variability for Year-to-Year Percent Changes in Gross National Product, National Health Expenditures, and National Health Expenditures as Percent of GNP, 1966-1981¹.

Variable			Measures of Variability2
	Measures of Central Tendency		Standard Deviation	Standard Error	Coefficient of Variation of The Mean3
	Mean	Median
Gross National Product, Current Dollars	9.5%	9.3%	2.1%	0.550%	0.058
Implicit Price Deflator for GNP	6.3	5.6	2.2	0.560	0.090
Gross National Product, Constant Dollars	3.1	3.1	2.4	0.632	0.205
National Health Expenditures, Current Dollars	12.8	12.8	1.5	0.377	0.029
Implicit Price Deflator for National Health Expenditures	7.0	7.2	2.2	0.569	0.082
Real National Health Expenditures	5.5	4.7	1.4	0.367	0.067
National Health Expenditures as a percent of GNP	3.1	3.0	2.5	0.640	0.208

¹There are 16 annual percent changes for the period 1966-1981.

²ln textbook examples, measures of variability typically measure sampling variability, that is, variations that might occur by chance because a sample of the population is surveyed. As calculated in this paper (and for typical applied time-series analyses) measures of variability also reflect variability associated with evolving causal structures and variability associated with various types of non-sampling errors such as data processing mistakes, nonresponse, misreporting by respondents, etc. The calculated measures are approximate and are meant as a general guide. It is important to keep in mind the potential dangers of extrapolating historical measures of variability into the future. That is, there can be no guarantee that future variability will replicate historical variability.

³For cautions in using the coefficient of variation when the mean of the variable measures change, see Kish (1965, pp. 47-49).