# What is cross sectional data?

Cross sectional data set consists of a simple individual households forms cities countries regions or any other type of unit at a specific point in time.

How to interpret cross sectional data?
In economics, cross-sectional variables are usually denoted by the subset i with i taking values of 1,2,3,....N.for N number of cross sections. Now I am taking example Y denoted the income data we have collected for N individuals, this variable in a cross-sectional framework will be denoted by
Yi for i=1,2,3...N.
Cross sectional data are widely used in economics and other social science.in economics the analysis of cross-sectional data is associated mainly with applied micro economics.labour economics state and local Public finance business economics demographic economics and health economics are some of the prominent field in
data collected at a given point in time are used in this case to test microeconomics hypothesis and evaluate economic policies.

### What is time series data?

Time series data it consists of observations of one and more variables over time. It is arranged in chronological  orderand can have a different time frequencies such as bi annual, annual, quarterly ,monthly ,weekly ,daily and hourly.
Time series data are denoted by the subscript t. If why denoted the GDP of a country between 1990 and 2002 we denote that as
Yt for t=1,2,3......T
Where is equal 1 for 1990 and t=T=13 for 2002.
What is difference between time series and cross sectional data?
A key feature of time series data which makes them more difficult to analyse than cross-sectional data is that if nomic observations are commonly dependent across time that is most economic time series are closely related to their recent history .so while most economic tricks procedure can be applied in both cross sectional and time series data 6:00, in the case of time series more things needs to be done to specify the appropriate economic model.
What is panel data?
a panel data set consists of time series for each cross sectional member in the data set an example we could consider the sales and the number of employees for 50 forms over a five-year period.panel data can also be collected on a geographical basis for example we might have GDP and money supply data for a set of 20 countries and for 20 year period.
Panel data are denoted by the use of both I and t subscript which have used before cross sectional and time series data respectively.
Yit for t=1,2,3........T and i=1,2,3....N
To better understand the structure of panel data consider a cross sectional and the time series variable as N*1 and T*1 matrices respectively.

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