Combining target trial emulation and qualitative research to understand the effect of health visiting on child hospital admissions in England

Health visiting is a complex public health intervention in which specialist nurses work with families to support the healthy development of children up to five years of age. Using routinely collected administrative health data, we emulated a target trial to estimate the effect of enhanced health visiting services on potentially avoidable hospital admissions for children born in 10 local areas in England between 2016 and 2019. We found that receiving additional support from the health visiting team in the early weeks of life was associated with an increased odds of a child experiencing a potentially avoidable hospitalisation. Qualitative research and sensitivity analysis indicated that our effect estimate was likely biased due to residual confounding. An in-depth understanding of the intervention and the mechanisms through which treatments are assigned is crucial for a robust target trial emulation. A mixed methods approach can help to generate this knowledge at an early stage and identify data that will need to be accessed or collected for successful control of confounding.