Table 3 Questionnaire items^a per secondary outcome including item references

 Reflective

I compare different types of fruit and vegetables before I buy something.

[4]

I put fruit and vegetables on my shopping list in advance.

I think carefully about what fruits and vegetables I will buy.

I make a thoughtful choice for the fruit and vegetables that I buy.

I choose my vegetables and fruit attentively.

 Habitual

Buying fruit and vegetables is part of my routine.

[5, 6]

I always buy the same fruit and vegetables.

I buy fruit and vegetables on autopilot mode.

Buying fruit and vegetables is typically something for me.

Buying fruit and vegetables is something I do by default.

 Impulsive

I buy fruit and vegetables if I feel like it.

[4, 7, 8]

I buy fruit and vegetables spontaneously.

I buy fruit and vegetables on a whim.

I buy fruit and vegetables if it comes to mind.

I buy fruit and vegetables when I see a special offer.

 Health goals

I think it’s important to eat healthy.

[9, 10]

 Healthy shopping

Healthy products are available in my supermarket.

[11, 12]

In my supermarket it is easy to do healthy shopping.

 Perceived social norm

Others in my supermarket buy healthy products

[13]

My friends and family eat healthy.

 Attractiveness healthy foods

Healthy products are tasty.

[14]

CUSTOMER SATISFACTION

How satisfied are you with your Coop supermarket in general (very unsatisfied-very satisfied)

N/A

To what extent are you satisfied with... (very unsatisfied-very satisfied)

…the supermarket environment and atmosphere?

…the supermarket layout and routing?

...the supermarket tidiness?

…the assortment of food products?

…the general product prices?

...the product discount prices?

…the fruit and vegetable prices?

…the bread prices?

I want to eat healthy.

N/A

 Reasons for heathy eating

The reason I want to eat healthy is…

…because this is important for good health.

…because it fits my life goals.

…because I would feel bad about myself if I did not.

…because I feel pressure from others to do this.

[15]

PERCEPTIONS DURING GROCERY SHOPPING

Grocery decisions

What do you think about your groceries choices bought at your Coop supermarket?

…I feel that my choices fit my personal preferences perfectly.

…I feel that I have been able to influence my choices.

…I am satisfied with my choices.

…These were choices I could not make very well.

[16]

 Shopping experience

How did you feel doing your shopping in your Coop supermarket?

…I felt patronized when choosing my groceries.

…I felt encouraged to choose healthy products.

…I felt invited to choose healthy products.

[17]

 Nudge awareness

Have you noticed anything in the supermarket in the past 12 months? (yes/no)

[18]

If so, what have you noticed? (free text)

Appreciation

I appreciate it when the supermarket helps me to make healthy choices.

In the last four weeks (baseline)/ three months (follow-up 1)/ six months (follow-up 2 and 3),…

[19, 20]

 Consequences of behaviour

...I have searched for and/or red information about the (health) benefits of walking

 Social comparison

...I noticed how much I walked compared to others.

 Action planning

...I planned in advance when and where I would go hiking.

 Self-monitoring

...I kept in mind whether I walked enough.

 Social support

..I have searched for support from others to walk enough.

 Goal setting

...I have set achievable (yet challenging) walking goals for myself.

 barrier identification

...I looked for tips on how to overcome barriers to walking (such as too little time).

 Self-evaluation

...I checked with myself how satisfied I am with my walking behaviour.

 Encouragement

...I looked for and/or read information that encouraged me to walk enough.

 Others’ approval

...I paid attention to what others think of my walking behaviour.

COMMUNICATION

The coaching app…

[21]

...invites me for a conversation

...is open to a conversation with me

…uses conversation style communication with me

…tries to communicate with me in a human voice

…tries to make communication interesting for me

…tries to make communication with me fun

…would admit an error to me

…treats me as a human being

...trying to force something on me

…appears patronizing

USE OF COACHING APP

In the past three months, have you used a subscription with a mobile internet data bundle on the smartphone on which the walking coach is installed? (yes/no)

How much data could you use monthly within your mobile internet data bundle? (five categories: 1/5/10/more than 10 GB per month, or: I do not know)

How often do you read the messages you receive from the walking coach? (never-always)

Which functions or characteristics of the walking coach are you positive about? (free text)

Which functions or characteristics of the walking coach are you negative about? (free text)

Do you have any other comments about your experiences with the walking coach? (free text)

N/A

 Perceived ease of use

How the walking app’s user environment works is…

...easy for me to learn.

...clear for me to understand.

...easy for me to understand.

[22]

 Perceived usefulness

The walking app…

…is helpful for me to keep track of my daily walking goal.

…is valuable to me to track progress towards my daily walking goal.

…works well for me to keep working towards my daily walking goal.

…is helpful to me in meeting my daily walking goal.

[22]

SELF-REPORTED WALKING BEHAVIOUR

Thinking about the past 4 weeks, on how many days did you walk for at least 10 minutes in a row?

On the days when you walked for at least 10 minutes, how much time did you usually spend walking?

[23]

PRIVACY CONCERNS COACHING APP

Because I used the walking app…

…I have the feeling that others know more about me than I would like.

…I think others can see my private information.

…I feel that my private information can be misused more easily.

[24]