A Singapore Government Agency Website

Official website links end with .gov.sg
Secure websites use HTTPS
Look for a lock () or https:// as an added precaution. Share sensitive information only on official, secure websites.
Sign In
Skip Navigation LinksLabour Market Statistics and Publications > Concepts > Seasonal Adjustment Concepts and Definitions
Seasonal Adjustment Concepts and Definitions
SAMPLE DESIGN
Switch statistical concept
Using Mean, Median or Mode Mean Median ModeA Measure Enabling Comparison Absolute vs Relative Change Annualized Percentage Growth Distribution Incidence From Sample to PopulationSample Reliability Seasonal Adjustment Percentiles Quantitative vs Qualitative Range Ratios Stock and Flow

Concepts and Definitions

In analysing labour market statistics, we are often interested in understanding how the indicator has changed over time, for example compared with the previous quarter or the same period last year.


Time Series 

A time series refers to a sequence of observations on a specific variable, collected over periodic time intervals, e.g. a day, week, month, quarter, or year.

Examples:
imas  Number of persons in the labour force in June each year ​ ​ ​
imas  Change in employment in each quarter ​ ​ ​
imas Number of job vacancies at the end of each quarter ​ ​ ​
imas Overall unemployment rate measured at quarterly intervals (refer to chart in Example 1) ​ ​

 

Seasonality 

Seasonality refers to the periodic variation in a time series that repeats in the same period each year.

Example 1

The unemployment rate typically increases form March to June and decreases from June to September. Unemployment is typically higher in June, when final year students from universities look for jobs, and seek vacation jobs during their mid-year break.
 
Overall Unemployment Rate
(Non-Seasonally Adjusted)
 
                            

 

Example 2

Resignation rate is typically lower in the last quarter of the year (i.e. October to December). Given that year-end bonuses are typically paid out during this time of the year, employees who intend to change jobs may decide to stay on and receive their bonus first, before moving to a new job.

Average Monthly Resignation Rate
(Non-Seasonally Adjusted)
 
If a time series periodically increases (or decreases) at same periods during the year, it will be difficult for us to analyse whether the changes in the indicator are a true reflection of economic or labour market conditions or merely due to seasonal influences. To better discern the trend (or long-term movement of the variable) and cyclical patterns (a component of the series that changes with the economic cycle) in the time series, many national statistical agencies apply a statistical technique known as seasonal adjustment to the time series to remove the seasonal influences. This can be done using statistical software with seasonal adjustment functionality. Time series with seasonal influences removed are called seasonally adjusted series.