Dear Michiel,

I am facing some issues to generate a design whithin design. I have a choice behavior to model in which buyers choose among alternatives sequentially. It is a treatment choice context, where persons usually choose combos of products for a sequential application. For example, one person can choose brand A for the first application, brand B for the second one, brand A again for the third, and so on. Thus, the number of applications may vary across people, although rarely they choose to make just one application (most of time they make combos of three brands).

To deal with such situation, I could generate a desing with scenarios (section 8.5 of the Ngene Manual), where the scenarios would be the applications. And I would ask the respondents to consider each scenario independently of all others. Below is a example (with only 3 brands and with the number of applications equal 3).

Design

;alts = altA, altB, altC, altD, altE

;rows = 15

;eff = (mnl, d, fixed)

;model:

U(altA) = b[-0.2] + b_price_A[-0.03] * PRICE_A[50, 80, 100, 120, 150] + b_appl[-0.5] * APPL[1,2,3] /

U(altB) = b[0.2] + b_price_B[-0.01] * PRICE_B[100, 160, 200, 240, 300] + b_appl * APPL[APPL] /

U(altC) = b[-0.5] + b_price_B[-0.01] * PRICE_B[100, 160, 200, 240, 300] + b_appl * APPL[APPL] /

U(altD) = b[0.5] + b_price_C[-0.02] * PRICE_C[150, 240, 300, 360, 450] + b_appl * APPL[APPL] /

U(altE) = b_price_C[-0.02] * PRICE_C[150, 240, 300, 360, 450] + b_appl * APPL[APPL]

$

1) My firts questions is about how to deal with the variation in number of application. I thought about using a opt-out alternative. Because some people may make no more than one choice in "real life" (while others may make up to 4), adding the opt-out alternative could help to guarantee that I will not estimate parameters based on forced responses for non "real life" preferences. Does this solution sound good? May you imagine an alternate solution? For example, could I generate a separate design for each respondent on the fly based on a pre/ setup question about number of apllications?

2) The second question is about partial choice set designs. Because I have 10 alternatives, I would like to show only a subset of alternatives in each choice task (section 8.11 of the Ngene Manual). Is there any issue in combining these two approaches (design whithin design and partial choice set designs)?

Thank you very much for your time.

Best regards, Rafael.