Relative Influence as a Running Tally
Kim P. Corfman and Donald R. Lehmann tested models of who prevails when two people make a purchase decision together, and found that two things consistently made the strongest contributions to relative influence. One is how intensely each person wants the thing. The other is who prevailed in the preceding joint decisions, which means influence accumulates across purchases and cannot be read off any single one.
What it is
The study sets out a conceptual framework for group decision-making under conflict and tests it with experimental data from couples making sequences of product choices. The models pit power-related resources against power-use-related goals as determinants of relative influence, which is the standard way this question is posed, and the result is that neither class of variable did as much work as relative preference intensity and the outcomes of preceding decisions. The second of those is the one no single-decision study can see, because it only exists in a sequence.
In effect
It is the most useful sentence in a thin consumer literature, because it reframes the unit of analysis. A couple choosing a sofa is not running one negotiation but continuing a series, and a concession made this week is partly a claim on next week. It also sets the limit on reading any observed joint decision as evidence about the people in it, since the same two people with the same preferences will produce different outcomes depending on where they are in the tally.
What it does not say
It does not come with a sample. The paper is closed, the number of couples is not established, and no figure is printed here. It is a 1987 experimental study of couples making product choices on paper, which predates the phone in the hand, the shared basket and the group chat, and the settings have changed in ways nobody has measured. And it says nothing about whether a joint decision is better or worse than an individual one, which is a comparison the consumer literature cannot make because a purchase has no agreed measure of quality.
Sources
- Corfman, K. P., & Lehmann, D. R. (1987). "Models of Cooperative Group Decision-Making and Relative Influence: An Experimental Investigation of Family Purchase Decisions." Journal of Consumer Research, 14(1), 1-13. doi:10.1086/209088. Abstract read in full; full text paywalled and not read, so the number of couples is not printed.
- Su, C., Fern, E. F., & Ye, K. (2003). "A Temporal Dynamic Model of Spousal Family Purchase-Decision Behavior." Journal of Marketing Research, 40(3), 268-281. doi:10.1509/jmkr.40.3.268.19234. Models influence strategies revised across decisions. Its stated purpose is to help marketers aim messages at the influential spouse, which is a limit worth printing.
- Dzhogleva Nikolova, H., & Lamberton, C. P. (2014). "Should Birds of a Feather Flock Together? Understanding Self-Control Decisions in Dyads." Journal of Consumer Research, 41(2), 361-380. doi:10.1086/676599. Seven studies; sample sizes not established. The best demonstration in reach that a joint decision is not the average of two individual ones.