Green Social Prescribing?

It's long been claimed that 'communing with nature' has a beneficial effect on human mental health. This appears to have been validated by the results of 7 UK-government supported pilot studies in England (https://www.theguardian.com/environment/article/2024/sep/04/better-than-medication-prescribing-nature-works-project-shows). The pilot studies involved more than 8000 people, who had been recommended by their social workers. Funding helped participants take part in activities, including nature walks; community gardening; tree planting and wild swimming in the sea or lakes. After taking part, the subject's assessed feelings of happiness/ regarding life as being 'worthwhile', improved to levels seen in the general population. Their levels of anxiety, showed 'significant' declines. Authors of a report on these studies, claim that 'green social prescribing' is cost-effective. The schemes cost about £500 per participant. Ten sessions of cognitive behavioural therapy costs around double this amount. These results are interesting but there are some limitations. Firstly, all the participants must have been nominated because they appeared unhappy/anxious to the social workers. What about the impact of such activities on less initially unhappy participants? Secondly, assessments of mood, are also not especially reliable. Thirdly, there's no appropriate control groups in these studies (people who didn't get to participate in activities but whose mood changes were assessed?). It certainly seems possible that confirmation bias (getting what's expected), could creep into the analysis. Fourthly, perhaps the biggest problem with the simple interpretation, is that all the 'prescribed' events were social activities. Was it contact with nature or humans (perhaps even a combination?), that made participants feel happier and less anxious?