maximum value the category could obtain). Those estimations allowed
us to identify the relative value of some categories in relation to others.
To cross-check responses, on November 2010 we followed the
same procedure to conduct the valuation of home garden ecosystem
services with a scientific panel. We used a purposive sample to generate the panel. The panel was integrated by seven scientists from the
Institut de Ciència i Tecnologia Ambientals (ICTA) of Universitat
Autònoma de Barcelona (UAB) working in the field of ecosystem
services and willing to answer the survey. Each member of the
panel independently valued their conformity with the 19 statements
about ecosystem services provided by home gardens, using the same
questionnaire than stakeholders.
Finally, we ran a power correlation analysis to examine the similarity between both sets of responses. For the statistical analysis we
used STATA 9 for Windows.
3.3. Limitations
The study has some methodological limitations that should be
taken into consideration for future research planning. First, by asking
stakeholders to rank a service based on a pre-written positive statement we can introduce a positive bias in the score given by the stakeholders, so our results might overvalue stakeholder's valuation of
home garden ecosystem services. Second, our measures are indicative
since in Likert scales numbers only act as qualitative indicators of
agreement to a statement. Therefore the quantitative interpretation
should be taken with caution. Third, some services could be included
in more than one category, for example the service “Maintenance
of landraces” was included under habitat services for the role they
play in maintaining genetic diversity, but it could also be embedded
in the category of production services under “Provision of landraces”.
Since we only included each service in one category, the total score of
each category should be taken as a relative measure. Fourth, the list of
services was drafted by the authors based on qualitative methods. We
are aware that this list does not covered all ecosystem services, e.g.
“carbon sequestration”, and that it is possible that we underestimated
the total number of ecosystem services delivered by home gardens.
Finally, the results presented here are stakeholders’ and scientist
perception, and the perception could be biased by a large number of
factors such as the research scale, i.e. extension of the garden area,
context, and the like.