Propositions for Modeling household decision-making
Eric J. Miller
University of Toronto Website
This paper lays out a theoretical framework for modeling household level decision making process, which covers many of the decisions needed as inputs to the integrated land-use, transportation and environment (ILUTE) simulation model. The focus is mostly on developing the “semantics” and “processes” which govern the theoretical decision making model. The semantics include concepts such as the project, project agenda, activity, activity episode and activity schedule used in the activity scheduling model.
Several basic assumptions are made on the future models that would be created to satisfy the theoretical framework. The most basic assumption is that the models will be an agent-based microsimulation model of household decision making. In the model activities are constrained by time, money, physical environment, etc. The framework gives formulations for time consumption, resource consumption, expenditures. It defines project, activity, activity type, activity mode (how the activity is accomplished) so that the models can be more universally applied. The projects are the higher level goals of the person (or household) which contain related tasks that are used to achieve a common goal. Each project contains a task list which is a list of all the steps that are required to complete the project, and an agenda, which is a list of all the current activities which may be added to the schedule (a more specific subset of the task list). In other words, the task list is similar to a list of all activities required by the project, while the agenda is a list of activity episodes that will be attempted to add to the schedule. The project agendas are developed for each project independently, and then the person scheduler adds activity episodes from the agendas and resolves conflicts. All of this is done within the framework of the household, which has its own project agenda. It is theorized in the paper that there exists a list of primary projects of which all conceivable projects are a subset.
It is assumed in the paper that activities fall into four basic types, with varying modes (which make the activity more specific, i.e. the basic list of activities would include acquire information, which could apply to any culture, and a mode such as surf internet which adds specificity to the activity). The four types of activities are “ongoing with external agent” (work), “one-time contracts” (doctor visit), “within household” (maintenance) and “serve-dependent” (supervise child). The model assumes that the contract activities (type I and II) are highest priority, with type one pre-planned as an skeleton schedule and type two has highest priority but only a weekly probability of occurrence. Serve-dependent activities are also high priority, as they are mandatory at the household level.
In developing the household scheduling process several hypotheses were made by the author. First, that scheduling is a sequential process, where activities are scheduled as their need arises. The provisional schedule can therefore be changed as needed as new activities are fit from the project agendas. Because of this, the scheduling process does not have an optimal outcome. In other words, the
maximizing solution is not necessarily or likely chosen, since activities are added sequentially and all potential patterns are not investigated. The author also states, that for many choices utility based solutions will be needed.
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