Two experiments in one: How accounting for context matters for welfare estimates

- A voluntary contributions mechanism (VCM) is mixed with willingness to pay (WTP).
- With the VCM, contributions are invariant across the order of mechanisms.
- WTP for milk bottles are sensitive to the order of mechanisms and to the period.
- WTP differences between milk bottles are stable.
- For each bottle, variations of WTP following a messages about attributes are stable.

By combining two different types of experiments in one experimental session, this paper aims at understanding how different contexts may influence participants' choices. This paper focuses on one hybrid experimental session that mixed one voluntary contributions mechanism (VCM), influencing the indemnity received by participants, and one mechanism eliciting willingness to pay (WTP) for milk bottles with public and private attributes. The VCM shows relatively high levels of contributions that are mainly influenced by the positive expectations of participants about the average group contribution, rather than by the variations in the design of this mechanism and the period of experiments. The WTP for milk bottles are particularly sensitive to the order of mechanisms and to the period of experiments. Conversely, the WTP differences between milk bottles for a given round of information are invariant across the order of mechanisms and the period of experiments. For each bottle, the variations of WTP coming from the messages about private and public attributes are also stable over the order of mechanisms and the period of experiments. This confers validity to experiments for measuring WTP for public and private attributes related to food. In other words, these variations of WTP contribute to welfare estimates and are useful to evaluate market regulations focusing on public and/or private attributes.