Adherence to nature-based social prescribing: a target trial emulation of RECETAS Prague study

Background

In pragmatic intervention studies, adherence often varies over time and depends on participant characteristics that also influence outcomes, potentially biasing conventional per-protocol analyses. Target trial emulation(TTE) provides a structured framework for estimating causal effects of adherence strategies, while avoiding selection bias during follow-up.

Methods

We analyzed data from the RECETAS Prague trial(n = 131), evaluating the 9-week nature-based social prescribing intervention Friends in Nature. Adherence strategies were defined by sessions attended and grouped (0-1, 2–5, 6–7, and 8–9). Outcomes included quality of life(EQ-5D-5L) and loneliness(De Jong Gierveld Score) at 3-months. A TTE framework with cloning, artificial censoring, and inverse-probability-of-censoring weighting estimated causal per-protocol effects. Missing data were handled using MICE(n = 5). Weighted generalized estimating equation models were fitted in each imputed dataset, and estimates were pooled using Rubin’s rules. Overall influence was assessed using a test for trend.

Results

Compared with attendance of 0-1 sessions, EQ-5D scores at 3 months were similar for 2–5(0.008; 95%CI −0.02 to 0.04), 6–7(0.014; 95%CI −0.02 to 0.05), and 8–9(0.008; 95%CI −0.03 to 0.05). Loneliness scores were also similar (2–5: −0.587; 95%CI −2.10 to 0.92; 6–7: 0.157; 95%CI −1.19 to 1.50; 8–9: −0.090; 95%CI −1.73 to 1.55) (test for trend: p = 0.303).

Conclusions

This study shows that TTE can provide a transparent framework for estimating adherence-related effects under time-varying participation in pragmatic trials. No differences in quality of life or loneliness were observed across attendance levels at 3 months, suggesting that longer intervention or follow-up periods may be needed to detect potential effects. However, residual confounding from unmeasured attitudes and differential compliance, particularly lower comparator adherence due to the non-blinded study design, may limit causal interpretation.

Key messages

• TTE offers a transparent framework to estimate adherence-related effects under time-varying participation in pragmatic public health trials.

• No 3-month differences in quality of life or loneliness were observed across attendance levels, suggesting longer intervention or follow-up may be needed.