BMJ  2006;332:178 (21 January), doi:10.1136/bmj.332.7534.178-b

Letter

Dummies and SIDS

Low response rates generate considerable uncertainty

Editor—Li et al found that in infants who died from sudden infant death syndrome (SIDS) the reported use of a dummy (pacifier) in the index sleep was 4.1%, in the 50% of eligible mothers who agreed to take part.¹ The use of a dummy in the other 50% of eligible infants with SIDS is unknown. In the control infants the reported use of a dummy in the last sleep before interview was 23.6%, in the 40% of eligible mothers who agreed to take part. The use of a dummy in the other 60% of control infants is also unknown.

Thus, potentially the overall dummy use in all the cases was between 2% and 54% and in all the controls between 9% and 69%. None of the confidence intervals reported in the paper reflects uncertainty generated by those who declined to take part. Because of the low response rates, unadjusted odds ratios of anywhere between 0.01 and 7.7 are compatible with the study findings, when the total eligible population is considered.

The authors conclude in their abstract that use of a dummy seems to reduce the risk of SIDS, but it could just be that reported dummy use in infants who died from SIDS was low because more mothers who gave their infants dummies declined to take part in the study.

The abstract also concludes that use of a dummy possibly reduces the influence of known risk factors in the sleep environment, but this is based on a spurious use of confidence intervals for the subgroups involved.² The more correct test of interaction reported in the results section showed that the difference in odds ratios between infants who did or did not use a dummy was not significant.

Manor View Practice, Bushey Health Centre, Bushey, Hertfordshire WD23 2NN chriscates{at}nhs.net

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Competing interests: None declared.

References

1. Li D-K, Willinger M, Petitti DB, Odouli R, Liu L, Hoffman H. Use of a dummy (pacifier) during sleep and risk of sudden infant death syndrome. BMJ 2006;332: 18-21. (7 January.)[Abstract/Free Full Text]
2. Altman DG, Bland JM. Statistics notes: interaction revisited: the difference between two estimates. BMJ 2003;326: 219.[Free Full Text]

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