The following table includes the number of white women over the age of 20 in the civilian labor force.Because it is time series data,what would the entries of the first column refer to? 
Source: http://data.bls.gov
Definitions:
Ionic Compounds
Chemical compounds composed of ions held together by electrostatic forces termed ionic bonding, typically formed between metals and non-metals.
Transfer of Electrons
A fundamental process in chemistry where electrons move from one atom, ion, or molecule to another, driving various chemical reactions and energy production.
Neutrons
Subatomic particles found in the nucleus of an atom, having no electrical charge and a mass slightly greater than that of protons.
Protons
Positively charged subatomic particles found in the nucleus of an atom, contributing to the atom's mass and defining the element's atomic number.
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