The challenges of seasonal adjustment for the Current Employment Statistics survey during the COVID-19 pandemic

For its seasonally adjusted data, the Bureau of Labor Statistics (BLS) seeks to remove all fluctuations that are caused by the yearly cycle of seasons. The coronavirus 2019 pandemic posed a challenge to this task, because its effect was strong, across the entire economy, and lasted for at least several months. To ensure that the effects of the pandemic were not being incorporated into the seasonal adjustment factors, the Current Employment Statistics program took additional actions such as splitting the seasonal adjustment into two runs (prepandemic and postpandemic) and incorporating additional types of outliers into its models. Most series published by the Current Employment Statistics (CES) program have a regularly recurring seasonal movement that can be measured from past data. Seasonal adjustment eliminates the part of the change attributable to the normal seasonal variation to help provide a better interpretation of trends without the influence of regularly occurring seasonal patterns.