Let X be N(0, 1). Find the pdf of Y = |X|, a distribution that is often called the half-normal. Hint: Here y ∈ Sy = {y : 0 < y < ∞}. Consider the two transformations x1 = −y,−∞ < x1 < 0, and x2 = y, 0 < y < ∞.

EVIDENCE-BASED PUBLIC HEALTH The PERIE Approach ● Problem ● Etiology ● Recommendations ● Implementation ● Evaluation How can we describe a health problem ● The burden of disease ○ Morbidity = disability ○ Mortality = death ● Course of disease ○ How often it occurs ○ How...