This research was conducted in accordance with approved guidelines, and all protocols were received Institutional Human Research Ethics Approval (Behavioural & Social Sciences Ethical Review Committee, University of Queensland), project number 2012000869. Informed consent was obtained from all respondents. The full survey is available in the Supplementary material.
We surveyed 1538 Brisbane residents aged 18–70 years to obtain information on health and experiences of nature. The survey was delivered online by Q&A Market Research Ltd to their existing market research database of potential respondents, and carried out in November 2012. This time period was chosen as it is prior to the onset of higher summer temperatures, ensuring that the outcomes were minimally affected by seasonal conditions and because it is prior to the summer holiday period which could also affect participation and the measured behaviors53. Brisbane City has high overall levels of public green space (>200 m2 per person) and tree cover (36%), both of which are spread rather evenly across the socio-economic gradient54. Thus baseline exposure to nature outside of the experiences measured in this study (i.e. through day-to-day activities at home or work) is likely to be high across city residents.
The respondent group was recruited based on whether they fulfilled a number of stratification criteria across a range of factors, which ultimately ensured that the socio-demographic distribution closely reflected that of the actual population (Table S1), according to age (similar numbers above and below 45), sex (similar numbers of males and females), income quartiles within the city, and respondents’ addresses were spread evenly among four spatial zones reflecting the four quartiles of tree cover across the city (Figure S1). A Pearson’s rank sum test was conducted to compare the proportion of representation within the different stratification criteria against that of the real population, and showed that the characteristics of the surveyed population were well correlated with that of the actual population (correlation coefficient = 0.67, t = 7.14, p < 0.0001).
Socio-demographic variables that are tied to health outcomes were collected, including age, sex, personal annual income, highest formal qualification, presence of children under 16 in the home, the primary language spoken at home, and number of days the respondent normally spends at work per week. Respondents also provided information on their height and weight, from which we calculated BMI. The Australian census-derived Index of Relative Socio-economic Disadvantage (IRSD) was used as a measure of the level of socio-economic disadvantage in the respondent’s neighbourhood, calculated for the finest possible spatial scale (Statistical Area 1, mean area = 0.44 km2,55). We also measured a person’s connection to nature using the Nature Relatedness scale33, as this could moderate any benefits gained from experiences of nature. All variables are described in detail in Table 3.
Table 3 Descriptions of the variables tested for correlation with each of the four health responses.
How to cite this article: Shanahan, D. F. et al. Health Benefits from Nature Experiences Depend on Dose. Sci. Rep. 6, 28551; doi: 10.1038/srep28551 (2016).