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. 1999 Jun;83(6):643–645. doi: 10.1136/bjo.83.6.643

Bias due to incomplete follow up in a cohort study

P Pennefather 1, W Tin 1, M Clarke 1, J Dutton 1, S Fritz 1, E Hey 1
PMCID: PMC1723091  PMID: 10340968

Abstract

AIM—To investigate the bias introduced by incomplete follow up in a cohort study of ocular outcome after premature birth.
METHODS—A geographically defined cohort of children born before 32 weeks' gestation was prospectively recruited at birth to study the ocular outcome at 2 years. On the basis of attendance at 2 years, the children's families were allocated to one of three groups: group 1 attended for follow up, group 2 were difficult to trace, and group 3 were very reluctant for assessment. All children were examined by a single ophthalmologist, masked to these groupings.
RESULTS—558 children (98.8% of study group) were examined, of whom 505 were in group 1, 20 in group 2, and 33 in group 3. The groups which were more difficult to study (groups 2 and 3) showed a significantly higher prevalence of ocular abnormalities, including strabismus (p=0.02) and cicatricial retinopathy of prematurity (p=0.002) compared with those attending for follow up. Further, not all of these cases could have been identified by review of the children's previous records. Ocular abnormalities would be underestimated by 16% (11.3% in group 1 compared with 13.4% in the total cohort, p=0.77).
CONCLUSIONS—This study suggests that the prevalence of abnormalities would be underestimated by incomplete follow up, as those subjects who were most difficult to obtain for study had a significantly higher prevalence of abnormalities.



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Selected References

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  1. Burgess P., Johnson A. Ocular defects in infants of extremely low birth weight and low gestational age. Br J Ophthalmol. 1991 Feb;75(2):84–87. doi: 10.1136/bjo.75.2.84. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Campbell M. K., Halinda E., Carlyle M. J., Fox A. M., Turner L. A., Chance G. W. Factors predictive of follow-up clinic attendance and developmental outcome in a regional cohort of very low birth weight infants. Am J Epidemiol. 1993 Nov 1;138(9):704–713. doi: 10.1093/oxfordjournals.aje.a116908. [DOI] [PubMed] [Google Scholar]
  3. Catlett A. T., Thompson R. J., Jr, Johndrow D. A., Boshkoff M. R. Risk status for dropping out of developmental followup for very low birth weight infants. Public Health Rep. 1993 Sep-Oct;108(5):589–594. [PMC free article] [PubMed] [Google Scholar]
  4. Dowdeswell H. J., Slater A. M., Broomhall J., Tripp J. Visual deficits in children born at less than 32 weeks' gestation with and without major ocular pathology and cerebral damage. Br J Ophthalmol. 1995 May;79(5):447–452. doi: 10.1136/bjo.79.5.447. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Grögaard J. B., Lindstrom D. P., Parker R. A., Culley B., Stahlman M. T. Increased survival rate in very low birth weight infants (1500 grams or less): no association with increased incidence of handicaps. J Pediatr. 1990 Jul;117(1 Pt 1):139–146. doi: 10.1016/s0022-3476(05)72462-8. [DOI] [PubMed] [Google Scholar]
  6. Keith C. G., Kitchen W. H. Ocular morbidity in infants of very low birth weight. Br J Ophthalmol. 1983 May;67(5):302–305. doi: 10.1136/bjo.67.5.302. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Page J. M., Schneeweiss S., Whyte H. E., Harvey P. Ocular sequelae in premature infants. Pediatrics. 1993 Dec;92(6):787–790. [PubMed] [Google Scholar]
  8. Robertson C. M., Hrynchyshyn G. J., Etches P. C., Pain K. S. Population-based study of the incidence, complexity, and severity of neurologic disability among survivors weighing 500 through 1250 grams at birth: a comparison of two birth cohorts. Pediatrics. 1992 Nov;90(5):750–755. [PubMed] [Google Scholar]
  9. Tin W., Fritz S., Wariyar U., Hey E. Outcome of very preterm birth: children reviewed with ease at 2 years differ from those followed up with difficulty. Arch Dis Child Fetal Neonatal Ed. 1998 Sep;79(2):F83–F87. doi: 10.1136/fn.79.2.f83. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Wariyar U. K., Richmond S. Morbidity and preterm delivery: importance of 100% follow-up. Lancet. 1989 Feb 18;1(8634):387–388. doi: 10.1016/s0140-6736(89)91764-9. [DOI] [PubMed] [Google Scholar]
  11. Weisglas-Kuperus N., Baerts W., Fetter W. P., Sauer P. J. Neonatal cerebral ultrasound, neonatal neurology and perinatal conditions as predictors of neurodevelopmental outcome in very low birthweight infants. Early Hum Dev. 1992 Dec;31(2):131–148. doi: 10.1016/0378-3782(92)90040-n. [DOI] [PubMed] [Google Scholar]
  12. Wolke D., Söhne B., Ohrt B., Riegel K. Follow-up of preterm children: important to document dropouts. Lancet. 1995 Feb 18;345(8947):447–447. doi: 10.1016/s0140-6736(95)90425-5. [DOI] [PubMed] [Google Scholar]

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