Hi Dangi,

I can say nothing to your first questions, it seems very domain specific...

However the second one: there is a theoretical and an empirical solution.

Theoretical: Narrow down your research questions. Do you really need all of the questions in order to be able to answer your research questions, or is this study a kind of  descriptive survey (data mining)? In other words, when you do have specific hypotheses regarding your DVs, which you want to test. Then do it. When you have DVs for which this is not the case, drop them, when explorations are not of 'genereal interest'.

Empirical: Conduct a pilot study, then run a factor (axis, not component) analysis over it, find out whether some questions correlate highly (loading on the same factor), which means they actually carry the same information (which hopefully makes sense on a psychological level). Then select items from these clusters, and use one or two questions were you had 10 before. There is definitely more going on regarding the selection criteria (also on a theoretical level, like plausibility), but also measurement accuracy. But this approach would be useful, when you are planning to use this kind of questionnaire more than once. That is, it could be useful from an economical perspective.

Hope this helps,

best René

Depending on how to meassure the impact of eco-labels on the purchase decision of organic food, you might try choise models. It allows you, for example, to estimate willingness to pay for eco-labels.

 Thank you all for taking the time to answer my query

Dear Dangi,

to select items for the TPB instrument, authors of a recent paper have used a qualitative approach. First, two raters have separately identified the most important items. Second, ICC has been calculated.

https://www.researchgate.net/publication/274141664_Using_the_theory_of_planned_behavior_to_identify_key_beliefs_underlying_pro-environmental_behavior_in_high-school_students_Implications_for_educational_interventions

Good luck with your study.

Article Using the theory of planned behavior to identify key beliefs...

Thanks for your valuable comments and suggestions