Introverts are nowhere near half the population. 25-30% are the figures usually cited.
The source that substantiates that introverts are close to half the population is the "MBTI® Manual: A Guide to the Development and
Use of the Myers-Briggs Type Indicator" by Isabel Briggs Myers, Mary H. McCaulley, Naomi L. Quenk, and Allen L. Hammer.
Nancy Ancowitz is a business communication coach, an adjunct instructor at NYU, and the author of Self-Promotion for Introverts (McGraw-Hill).