What is the behavioral styles identified by alexander Thomas and Stella Chess in their early research on infant temperament?

Alexander Thomas and Stella Chess identified three primary behavioral styles in their research on infant temperament: easy, difficult, and slow-to-warm-up. Easy infants are generally adaptable, have a positive mood, and establish regular routines. Difficult infants tend to be more reactive, exhibit negative moods, and may struggle with changes in routine. Slow-to-warm-up infants are initially hesitant or shy but can gradually adapt to new situations with time.