What is still unknown regarding the effect of different scales of biophilia (none, small-scale, or large-scale) on the well-being of employees, and how can a fitting study be constructed?


A vast interest in the benefits of plants and well-being has risen in recent years. It is commonly understood that exposure to nature is beneficial for people, and we are gaining an increasing amount of knowledge about the positive impacts of bringing greenery indoors to improve air quality, reduce stress and/or support cognitive wellness of the building’s occupants.


Considering that we spend an average of 90% of our lives indoors, where 60% of our waking hours are spent working in an indoor environment, we need to better understand the benefits of biophilia work environments.

A substantial amount of research has shown that plants can enhance task performance, productivity, attention, workplace satisfaction, lower stress levels, and, decrease rumination. Pei and colleagues (2015) found that occupants of green buildings have significantly higher satisfaction rates than conventional buildings.


Hähn et al. (2020) found that the introduction of two plants per person for two weeks positively affects productivity. Yin et al. (2019) showed that exposure to biophilic design is correlated with a decrease in physiological stress.

Although there is a substantial amount of literature supporting the benefits of green, the data ON the optimal scale of greenery for well-being IS very limited as it is difficult to compare findings when every study uses different quantities, species, distances, and durations.



The International Well Building Institute (WELL), building standard V1 aims at enhancing occupant health and well-being, states that at least 1% of the floor area must be covered by plants, and one living wall should be included per floor. 


However, a small or large plant may have the same footprint but can vary greatly in impact due their overall volume.




To tackle the unknown, MOSS teamed up with 6 MSc students of Wageningen University in 2021 to design a study that explores the effect of no-, small-, or large-scale biophilia on the well-being of employees, and how a fitting study can be constructed. 


When measuring the impact plants can have on people, MOSS considers the importance to work with cubic metrics of the foliage. When only using surface area, as adhered to in the WELL building standard v1, it generates inconsistent results due to the variation in plant height.

“Small-scale indoor green” has not been defined by previous studies. Therefore, for this research, MOSS set the value of small-scale indoor green at 0.5% since it reflects the current and average amount of plants in offices. 
In contrast, MOSS established the value of “large-scale indoor green”, at an 8% plant-to-room volume since this is the benchmark realized in MOSS’s projects.


Two design methods are suggested by the researchers based on the circumstance of this study: parallel design and cross-over design. 

The parallel design can be considered as the less demanding design as the intervention will last three months, resulting in higher compliance of participants and lower cost. 


As each department receives one intervention, the result is therefore not as strong as it would be in a cross-over study. Because the departments must be compared to each other, this design requires a large number of participants.

Cross-over design are more costly and requires more time, approximately nine months. But as each participant is exposed to all three interventions, the results provide more certainty about the causal effects.


This means that also fewer participants are required for the analysis. Due to the lower compliance rate, it is hypothesized that these factors will balance out and require the same number of participants for recruitment. 

 Although the cross-over design is more complicated than the parallel design, it is a stronger method, as suggested by the researchers. 


To determine the sample size for the experiment, the students took calculations of other comparable research into account. Based on the sample size calculations of these different variables; productivity, concentration, workplace satisfaction, and stress, it can be seen that different variables need a different number of sample sizes to get statistically significant results, as illustrated below:

Number of required participants by each variable for this experiment 

Based on the student’s research, they helped plan an experiment in which productivity and workplace satisfaction are considered as the primary variables, and therefore the number of participants will be based on their power calculations, using the two-sample t-test analysis to determine if two population means are equal. 

For productivity, 200 employees should be invited (Larsen et al., 1998; Thatcher et al., 2020). To measure workplace satisfaction, close to 250 participants should be invited (Nieuwenhuis et al., 2014). 


The students concluded that 200-250 employees need to be invited for this experiment, expecting a final participation group of around 120-150 employees basing on the response rate of the Nieuwenhuis et al. (2014) experiment.

Concluding from the literature review, the main hypothesis for this experiment is that large-scale indoor green has a larger positive significant effect on general well-being, concentration, workplace satisfaction, rumination, productivity, and stress,  than small-scale indoor green. 

Check out MOSS LAB 1.1 for the execution of the experiment and the pioneering results!


Process Coach | Cor Langeveld

Academic Advisor | Tia Hermans

Controller | Shynar Makirat

Manager | Romee Heemstra

Secretary | Xi Yu