CVEN9407 Chap.1 Econometric Methodology and Transport Data
Econometric Methodology and Transport Data
The opening chapter sets out what econometrics adds to statistics: theory gives a direction, and estimation gives a magnitude with a measure of uncertainty. It follows a trip-generation hypothesis around the full econometric method, from stated theory to policy use, and then turns to data.
Crash records are observational, so the chapter covers cross-sectional, time series, pooled and panel layouts, the ratio, interval, ordinal and nominal scales, and the gap between association and causation that every project report must respect.
For the term project, this chapter is where the data section of every report begins.
Before any model is fitted you need to know which records you hold, how each field is measured, which layout each later model requires, and what the records cannot tell you because they were never designed as an experiment. Getting those decisions right in the first fortnight saves rework in every deliverable that follows.
What this chapter covers
- 01
Statistics and econometrics as the two halves of the course
- 02
The econometric method from theory to policy use
- 03
Mathematical versus econometric models and the error term
- 04
Observational data and its four layouts
- 05
Ratio, interval, ordinal and nominal scales
- 06
Regression, correlation and causation
Worked example · free
Identifying the layout of an intersection dataset
- 1The same 20 units are observed repeatedly through time, so the layout is panel (longitudinal) data.
- 1Five years give 60 months, so there are 20 x 60 = 1,200 intersection-month observations.
- 1Following the same sites lets the analysis separate differences between intersections from changes over time, which one cross-section of a single year cannot do.
Key terms
- Econometrics
- Econometrics is the use of statistical methods to put numerical values on relationships stated by theory, and to test them.
- Panel data
- Panel data follow the same cross-sectional units, such as road segments, through repeated time periods.
- Ordinal scale
- An ordinal scale ranks categories in a natural order without measurable gaps between them, as injury severity does.
- Observational data
- Observational data are recorded as events happen rather than generated under controlled experimental conditions.
- Interval scale
- An interval scale has meaningful differences between values but no true zero, so ratios between values are not meaningful.
Econometric Methodology and Transport Data FAQ
Why does the course start with methodology instead of formulas?
Because every later model follows the same route: state a hypothesis, write it mathematically, add an error term, collect data, estimate, test, forecast and apply. Knowing which step you are on makes it clear why each table belongs in a report and what question it answers.
Does a strong regression result prove that one factor causes crashes?
No. A regression describes how the average of one variable moves with others. Cause needs an argument from theory and a design that rules out other explanations, such as traffic volume driving both the explanatory variable and the crash count.
Why does the measurement scale of a variable matter?
The scale decides which summaries and models make sense. Means need interval or ratio data, ordinal outcomes suit ordered models, and nominal outcomes such as crash type call for a multinomial logit rather than a linear regression.
What is the difference between pooled cross sections and panel data?
Pooled cross sections stack separate samples taken at different times, so the units need not repeat. A panel follows the same units through every period. The distinction matters because a panel can control for fixed differences between sites, while pooled data cannot track any single site.
Can I treat a 1 to 5 agreement rating as a number?
Strictly it is ordinal, because the gap between 'agree' and 'strongly agree' is not a measured distance. Many analysts average such ratings anyway, but a careful report says so, checks whether conclusions change with the median, and prefers an ordered model when the rating is the outcome.
Assessment move
Draw the econometric method from memory, then label each section of your first project report with the step it represents. Go through the crash record fields and write the scale and the natural summary beside each one; that list becomes the data section of your report. Finally, practise rewriting a causal sentence as an association with a named alternative explanation.
Keep that field list beside you when you clean the data, because the scale of each variable decides how it can be recoded and summarised later.
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