URSI 403--Doing Urban Research -- Lecture Notes 3

II. Framing a "Theory "

A. Terms:

1. Concepts: "The function of scientific concepts is to mark the categories which tell us more about our subject matter than any other categorical sets. Whether a concept is useful depends on the use we want to put it to." A. Kaplan
2. Axioms: Propositions assumed to be true
   • Causal assertions, untestable because impossible to control relevant variables.
   • Implies direct causal links among variables
   • Temporal sequence of covariance
3. Laws:
   • Propositions proven to be true.
   • Successful inquiry of particulars establishes "fact," of general statements establishes "law."
4. Theories:
   • Must interrelate propositions, 2 or more at a time.
   • Ideally, minimal set of propositions (axioms) from which all other propositions may be derived by logic.
     • --correlation between nonadjacent, linked variables will be weak, hence need for few variables.
   • General Theory is small number of abstract variables, linked to measurable variables.
   • Auxiliary Theories link abstract theory to substantive problems.
5. Prediction
   • Short-run prediction does not need theory
   • If any major parameter varies, theoretical explanation is needed to make prediction.
   • Only small fraction of predictor variables are also explanatory.
6. Complexity: Generated in a number of ways
   • add more variables
   • more complex forms of relationship (nonlinear, nonadditive joint effects)
   • dynamic processes (time paths, feedbacks, cycles)
   • more realistic assumptions (measurement error, unexplained variation)

B. Rules: (Anderson)

1. Empirical verification: must correspond with observed reality.
2. Operational definition: define terms by the operations involved in manipulating or observing their referents.
3. Controlled observation: outcome must be observed under different values of input and when all other variables can be discounted as possible causes of any change in outcome. ("contrafactual")
4. Statistical generalization: random sample from the set of conditions to which you wish to generalize.
5. Empirical confirmation: consistency with other verified statements increases probability of truth.

C. Logic Linking Data to Propositions

1. Simplicity: small number of abstract variables linked in explicit way.
2. Validity
   • construct (operationalization)
   • internal (causal linkages)
   • external (domain)
   • reliability (replicability)

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