https://www.youtube.com/watch?v=cZssJ1SAESs&list=PLEUKy_nwlzwFbxj6ilK2XXHJqBXMcTOOc&index=5 ================================================================================ Subject: each person Factor or Concept Characteristics which subject has Variable: Factor Measurement By using rule, data is represented by symbol or number Data Collection of symbols or numbers ================================================================================ ================================================================================ 4 variables ================================================================================ ================================================================================ ================================================================================ Cross-sectional data data which is obtained from one time ================================================================================ Longitudinal data Time series data data which is obtained from continuous time ex) stock prices, GDP variation from 2010 to 2014 ================================================================================