Understand Data Basics

• Data are collected over a single time period (e.g., records are from a specific year). 
• Allows the comparison of characteristics between units or groups at a fixed point in time. 

From the table below, it can be seen that in 2022, there were 6 males and 4 females. Of the 4 females, only 1 lives in HDB housing while the rest live in private estates. 

• Data are collected at several points in time. 
• Data can be collected/ observed at different frequencies such as hourly, daily, weekly, monthly, quarterly, or annually. 
• Ordering of records by time matters since there is a time dimension. 
• Time series data allow us to identify and analyse trends or behaviours over time. Table 2 shows an upward trend in the number of individuals with higher education levels (e.g., Diploma, University) from 2017 to 2022, and a downward trend in the number of those with Secondary education or below. 
• Other examples include interest rates (monthly), exchange rates (daily), GDP (annually), inflation (monthly, annual). 

• Combines time series and cross-sectional data, but observations in each cross section do not necessarily refer to the same unit. 
• For example, individuals across the years can be randomly sampled to obtain multiple years of cross-sectional data, and these datasets can be combined together. 
• The main advantage of pooled data over cross-sectional data is that the former is typically a larger sample, since multiple cross-sectional data are combined from different time periods. 

• Combines cross-sectional and time series data, similar to pooled data. The difference is that the same cross-sectional units (e.g., individuals) are observed at several points in time (days, months, years, before and after event etc.). It is also known as panel data. 
• Allows the observation of the same group over a period of time, and track the changes over the period. This is useful for detecting development trends or changes in the characteristics of interest. Hence, panel data are often used in studies that investigate the effects of certain events, policies or treatments. For example, the effects of a particular government policy on the wages of individuals can be studied by looking at the change in wages within individuals before and after policy implementation.