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The impact of early transfer bias in a growth study among neonatal intensive care units
Irene E Olsen1, Douglas K Richardson, Christopher H Schmid
1Department of Nutrition, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA 02212, USA. olseni@email.chop.edu
Insights
Transfer bias in neonatal intensive care units (NICUs) can skew study results. Sampling strategies effectively reduced this bias in a study of extremely premature infants, proving more successful than replacement methods.
Area of Science:
- Neonatal care
- Clinical research methodology
- Biostatistics
Background:
- Comparisons of neonatal intensive care unit (NICU) performance can be biased by infant transfers between facilities or discharge home.
- This bias, termed transfer bias, can significantly impact the validity of research findings.
Purpose of the Study:
- To quantify the potential size of transfer bias in a large cohort study of extremely premature infants.
- To evaluate strategies for minimizing transfer bias in neonatal intensive care unit research.
Main Methods:
- A neonatal growth study restricted eligibility to infants born at <30 weeks gestation.
- Early transfers (before day of life 16) were managed by substituting matched replacements.
- The study involved six tertiary neonatal intensive care units.
Main Results:
- The restriction strategy significantly reduced the overall early transfer rate from 16.4% to 3.6%.
- The range of transfer rates among NICUs narrowed from 0.6-32.7% to 0-11.0%.
- Matched replacement had a limited effect due to the low number of early transfers and matching limitations.
Conclusions:
- Sampling strategies to minimize infant loss to follow-up were more effective than replacement strategies in reducing transfer bias.
- While complete elimination of transfer bias may be impossible, minimizing, quantifying, and testing its effects are crucial for valid NICU studies.
Background And Objective:
Transfer of infants between hospitals or their discharge home may bias comparisons of the performance across neonatal intensive care units (NICUs). This study attempts to show the potential size of transfer bias in the context of a large cohort study and describe strategies for minimizing this type of bias.
Methods:
To limit transfer bias in a neonatal growth study of extremely premature infants in six tertiary NICUs, we restricted eligibility to infants <30 weeks gestation at birth and substituted matched replacements for early transfers (infants transferred or discharged prior to day of life 16).
Results:
The restriction strategy was successful, reducing the overall early transfer rate from 16.4 to 3.6% and the range of transfer rates among individual NICUs from 0.6-32.7% to 0-11.0%. Replacement by matched substitutes had a much smaller effect because of the small number of early transfers and our inability to match on all factors distinguishing early transfers.
Conclusion:
Sampling strategies to minimize infants lost to follow-up were more successful than replacement strategies in limiting transfer bias in a NICU growth study. Although complete elimination of bias is likely impossible, valid studies require efforts to minimize, quantify, and test the effect of transfer bias.
