Network meta-analysis (NMA) is a common approach to summarize relative treatment effects from randomised trials with different treatment comparisons. Most NMAs are based on published aggregate data (AD) and have limited possibilities to investigate the extent of network consistency and between-study heterogeneity. Given that individual participant data (IPD) is considered as the gold standard in evidence synthesis, we explored statistical methods for IPD-NMA and investigated their potential advantages and limitations as compared to AD-NMA. We discuss several one-stage random effects NMA models that account for within-trial imbalances, treatment effect modifiers, missing response data and longitudinal responses. We illustrate all models in a case study of 18 antidepressant trials with a continuous endpoint (the Hamilton Depression score). All trials suffered from drop-out, and missingness of longitudinal responses ranged from 21 to 41% after 6 weeks follow-up.

Our results indicate that NMA based on IPD may lead to increased precision of estimated treatment effects. Furthermore, it can help to improve network consistency and explain between-study heterogeneity by adjusting for participant-level effect modifiers and adopting more advanced models for dealing with missing response data.

We conclude that implementation of IPD-NMA should be considered when trials are affected by substantial drop-out, and when treatment effects are potentially influenced by participant-level covariates.