Cross section data refers to the statistics collected from different parts of the population during the same period. Cross section data covers a cross section of population and information is collected from this cross section during a given period of time. For example, suppose we are collecting data on consumption expenditure of a group of families during any year. This data will be cross section data. Similarly, if we collect incomes of individuals during a particular year, it will give us a cross section data. Time series data are necessary when we are interested in the analysis of trend and cyclical or seasonal fluctuations. Cross section data are more useful in order to verify different functional relationships which are supposed to be invariant over time. Both types of data may be useful in the study of macroeconomic theory. For example, the consumption function hypothesis can be tested either with reference to time series data or with reference to cross section data.