Are the psychological tests valid?

Malecón Grau 260
Chorrillos
Lima 9
Perú
E-mail: epollitt{at}ucdavis.edu

Dear Sir:

The article by Black et al (1) provides insufficient information to claim that weekly administration of iron and zinc supplements benefits exploratory behavior. The iron and the iron-plus-zinc treatments had a significant effect on the orientation-engagement factor of the Bayley Behavior Rating Scale (2), which includes one item (out of 11) on exploration. This factor also includes items that assess "... arousal, positive affect, energy, initiative, enthusiasm, exploration, social engagement, and lack of fearfulness" (3). At issue is not a simple change of labels but whether the 11 items included in the orientation-engagement factor measure the concept of exploration. No evidence to this effect was presented, and the statement that "Orientation-engagement factor served as the measurement of exploration" trivializes both the scale and the very nature of construct validity (4). The definition of exploration should not be left to common sense; it requires careful consideration of the behavioral and developmental components of the concept.

There was no treatment effect on the Mental Development Index (MDI) from the Bayley Infant Development Scale II administered at 12 mo. This finding was not surprising. The MDI obtained at 12 mo has a track record of poor sensitivity to detect developmental delays secondary to micronutrient deficiencies, and its construct validity is questionable (5, 6). Accordingly, the authors could have predicted that the MDI would not discriminate among groups after treatment. The probabilities of detecting effects on the mental scale, if any were indeed present, would have increased if the authors had charted a developmental trajectory after age 12 mo (6, 7).

ACKNOWLEDGMENTS

The author had no conflicts of interest.

REFERENCES

1. Black MM, Baqui AG, Zaman K, et al. Iron and zinc supplementation promote motor development and exploratory behavior among Bangladeshi infants. Am J Clin Nutr 2004;80:903–103.
2. Bayley N. Bayley scales of infant development, II. San Antonio, TX: Harcourt Brace & Co, 1993.
3. Black MM, Matula K. Essentials of Bayley scales of infant development. II. Assessment. New York, NY: Wiley, 2000.
4. Anastasi A, Urbina S. Psychological testing. 7th ed. Upper Saddle River, NJ: Prentice Hall, 1997.
5. Grantham-McGregor S, Ani C. A review of studies on the effects of iron deficiency on cognitive development in children. J Nutr 2001;131:649S–66S.
6. Pollitt E. Developmental and probabilistic nature of the functional consequences of iron-deficiency in children. J Nutr 2001;131:669S–75S.
7. Pollitt E, Saco-Pollitt C, Jahari A, Husaini MA, Huang J. Effects of an energy and micronutrient supplement on mental development and behavior under natural conditions in undernourished children in Indonesia. Eur J Clin Nutr 2000;54:S80–90.