James P. Scanlan, Attorney at Law

NHANES ILLUSTRATIONS

(June 5, 2011)

The National Health and Nutrition Survey (NHANES) provides a wealth of data to illustrate the patterns described on the Scanlan’s Rule page.  Figure 7 of the 2008 ICHPR presentation[i] uses NHANES data on systolic blood pressure of black and white men to show, for example, how reducing systolic blood pressure will tend to increase relative differences in hypertension while reducing relative differences in rates of avoiding hypertension.  Figures 9 and 10 show some of the nuances of the patterns of absolute differences and odds ratios when the universe is restricted to the populations deemed hypertensive.

The Comment on Dowd and Aiello IJE 2008[ii] discusses the authors’ findings that a program of folate supplementation led to increasing relative differences in folate level (by race and socioeconomic status) and shows that, as commonly would occur in the circumstances, the relative differences in adequate folate decreased.

Table 1 below, which is based on NHANES 2005-2006 data, show the implications of increasing or decreasing overall folate levels.  Row 8 shows the actual situation with respect to whites and blacks falling below the minimum adequate folate level of 362.6 nmol red blood count.  The white rate of 4.42% and black rate of 17.22% translate into black/white ratio for low folate of 3.9 and a white/black ratio for adequate folate of 1.15.  If folate were improved such that everyone with a level of 342.6 or above now able to achieve adequate folate levels (Row 7), the black/white ratio for low folate would increase to 4.3 and the white/black ratio for adequate folate would decrease to 1.11.

On the other hand, if folate status generally worsened such that everyone previously with a folate level below 382.6 (Row 9) now had low folate, black/white ratio for low folate would have instead decreased to 3.58 and the white/black ratio for adequate folate would have increased to 1.19. 

Across the spectrum of values shown in the table the various measures behave generally as would be expected in the circumstances (according to the explanation set out in the introduction to the Scanlan’s Rule page) with some exception for the odds ratio.

The EES column shows the values according the approach described on the Solutions sub-page of the Measuring Health Disparities page.  The fact that the values changes reflects some of the shortcomings of that approach (as also reflected in Table 6 of the Comment on Boström and Rosen Scan J Pub Health 2003[iii] with respect to systolic blood pressure differences.)  But such approach remains the best available method of appraising differences when the underlying distributions are not visible.  In the case of the three rows discussed above the EES values were very close.