ILUTE

Social Networks andActivity-travel modelling:

some research ideas

Juan Antonio CarrascoUniversity of Toronto

Student Caucus WorkshopToronto, September 13, 2003

ILUTE

The importance of networks

ILUTE

Outline

• What is a social network?

• Why social networks?

• Potential ideas

• Potential methodologies

• Conclusion

ILUTE

What is a social network?

• Study of social structure and its effects

• Social structure = social network

ILUTE

What is a social network?

11 22

88

44

33

5566

77

Nodes (actors)

ILUTE

What is a social network?

11 22

88

44

33

5566

77

Relationships (ties)

ILUTE

Why social networks?

11 22

88

44

33

5566

77

Social network models

ILUTE

Why social networks?

11 22

88

44

33

5566

77

Activity-travel behaviour models

Are we doing a good job?

ILUTE

Why social networks?

• Axhausen (2002):– “Need to underpin our travel models with a better

understanding of the social structures of daily life and, as we implicitly forecast/speculate about them when we predict travel behaviour over long time horizons, anyway…”

• New perspective incorporation of social space

• Relationship between social and physical space

• Ties: “links” that indirectly represent potential activity and travel between the actors

• Need to explicitly incorporate interactions

ILUTE

Potential ideas

• De-emphasis on psychological and economic explanations– Focus on relationships– Behaviour from a different perspective:

• Contrasts with psychologistic explanations that treat individuals as independent units-of-analysis

• Social network data sets often include information about attributes, such as age, gender, ethnicity, and beliefs.

• However, network analysis does not treat social systems as the sum of individual attributes, but links attribute data with relational and structural data”

ILUTE

Potential ideas

• Representation of constraints and travel behaviour– “Behaviour is interpreted in terms of structural

constraints on activity, rather than in terms of voluntaristic inner forces” (Wellman and Berkowitz, 1988)

– Structural theory allow relationships to be asymmetrical

– Link with Hägerstrand's (1970) ideas

• Coupling interactions

• Capability physical – social space

• Authority asymmetry

ILUTE

Potential ideas

• Changes in the way people interact (Wellman, 2001)– Person-to-person door-to-door person-to-person– Information and communication technology (ICT)

• Specialization of networks– “Achieved” (e.g. lifestyle) versus “ascriptive” (e.g.

income) characteristics– Role-to-role relationships New ways to segment activities and travel

ILUTE

Potential methodologies

• Variety of descriptive and analytical tools:

– Centrality and prestige

– Locational properties

– Structural equivalence, position and roles

– Dyadic and triadic methods

ILUTE

Potential methodologies

• Statistical formation of ties and network formation– Simulation and statistical techniques (e.g. kinship)

– Stochastic simulation models “sociomatrix” as random variables:

• Distributions

• Random components

– Log-probabilistic models – Autocorrelation over the social space (similar to spatial econometrics)

– Representation of personal and “linked” lives

ILUTE

Conclusions

• Need to incorporate interactions among individuals

• Potential for applying concepts and theories

• Potential for applying methodology

• The challenge…

ILUTE

Social Networks andActivity-travel modelling:

some research ideas

Juan Antonio CarrascoUniversity of Toronto

Student Caucus WorkshopToronto, September 13, 2003