In statistics and econometrics, the term panel data refers to two-dimensional data. In marketing, panel data refers to data collected at the point-of-sale (also called scanner data).

Data are broadly classified according to the number of dimensions. A data set containing observations on a single phenomenon observed over multiple time periods is called Time Series. In time series data, both the values and the ordering of the data points have meaning.

A data set containing observations on multiple phenomena observed at a single point in time is called Cross-Sectional. In cross-sectional data sets, the values of the data points have meaning, but the ordering of the data points does not.

A data set containing observations on multiple phenomena observed over multiple time periods is called Panel Data. Alternatively, the second dimension of data may be some other than time. For example, when there is a sample of groups, like siblings or families, and several observations from every group, the data is panel data. Whereas time series and cross-sectional data are both one-dimensional, panel data sets are two-dimensional.

balanced panel:		unbalanced panel:

In the example above, two data sets with a two-dimensional panel structure are shown. Individual characteristics (income, age, sex) are collected for different persons and different years. In the left data set two persons (1, 2) are observed over three years (2003, 2004, 2005). Due to the fact that each person is observed every year, the left-hand data set is called an Balanced Panel, whereas the data set on the right hand is called an Unbalanced Panel, since Person 1 is not observed in year 2005 and person 3 only in 2004.

• German Socio-Economic Panel (GSOEP)
• Household, Income and Labour Dynamics in Australia Survey (HILDA)
• British Household Panel Survey (BHPS)
• Survey of Income and Program Participation (SIPP)
• Lifelong Labour Market Database (LLMDB)

• Livingston Survey
• ASA-NBER Survey of Professional Forecasters
• Blue Chip Survey of Professional Forecasters

Arellano, Manuel. Panel Data Econometrics, Oxford University Press 2003. [www.cemfi.es]

Hsiao, Cheng, 2003. Analysis of Panel Data, Cambridge University Press.

Davies, A. and Lahiri, K., 2000. "Re-examining the Rational Expectations Hypothesis Using Panel Data on Multi-Period Forecasts," Analysis of Panels and Limited Dependent Variable Models, Cambridge University Press.

Davies, A. and Lahiri, K., 1995. "A New Framework for Testing Rationality and Measuring Aggregate Shocks Using Panel Data," Journal of Econometrics 68: 205-227.

Frees, E., 2004. Longitudinal and Panel Data, Cambridge University Press.

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