DDI Controlled Vocabulary for Time Method


Describes the time dimension of the data collection.


Short Name:
Long Name:
Time Method
Version Notes:
Version 1.1 carries a new definition of CrossSection that clarifies how it differs from the Longitudinal method.
Canonical URI:
Canonical URI of this version:
Location URI:
Alternate format location URI:
Alternate format location URI:
Agency Name:
DDI Alliance

Code List
Value of the Code Descriptive Term of the Code Definition of the Code
Longitudinal Longitudinal Data collected repeatedly over time to study change in a population.
Longitudinal.CohortEventBased Longitudinal: Cohort/Event-based Data collected over time about a group of individuals that are connected in some way or have shared some significant experience within a given period. Examples: birth, disease, education, employment, family formation, participation in an event.
Longitudinal.TrendRepeatedCrossSection Longitudinal: Trend/Repeated cross-section Studies different samples/different groups of people from the same population at several points in time, using the same set of questions/variables. Conclusions are drawn for the population. Examples: public opinion polls, elections studies, etc.
Longitudinal.Panel Longitudinal: Panel Data collected over time from, or about, the same sample of respondents.
Longitudinal.Panel.Continuous Longitudinal: Panel: Continuous Reports from the panel are collected on a regular basis.
Longitudinal.Panel.Interval Longitudinal: Panel: Interval Measurements are taken only when information is needed.
TimeSeries Time Series Data collected repeatedly over time to study change in observations. These are typically "objective" measurements of phenomena that can be observed externally, as opposed to attitudes/opinions or feelings. Examples may include economic/financial indicators, natural/meteorological phenomena, vital statistics, etc.
TimeSeries.Continuous TimeSeries: Continuous Phenomena are measured at every instant in time. Examples: lie detectors, electrocardiograms, etc.
TimeSeries.Discrete TimeSeries: Discrete Measurements are taken at (usually regularly) spaced intervals. Examples: macroeconomics (weekly share prices, monthly profits, sales); meteorology (hourly temperature); measurements of individuals (blood pressure, weight, height); sociology (crime figures, employment figures), etc.
CrossSection Cross-section Cross-sectional data is data collected by observing subjects at the same point in time, or without regard to differences in time. Analysis of cross-sectional data usually consists in comparing the differences among subjects, but is not focused on studying change over time (adapted from Wikipedia).
CrossSectionAdHocFollowUp Cross-section ad-hoc follow-up Data collected at one point in time to complete information collected in a previous cross-sectional study; the decision to collect follow-up data is not included in the study design.
Other Other Use if the time method is known, but not found in the list.


The element TimeMethod is a string type in DDI 3.1, but will be changed to CodeValueType in DDI 3.2. Controlled vocabulary codes can still be used with this element in DDI 3.1, but it will not be possible to reference the external controlled vocabulary by using the attributes created for this purpose in CodeValueType.

Module Name Element Name
datacollection TimeMethod
Element Number Element/Attribute Name timeMeth@method

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