This lecture is from a course I taught at the Higher School of Economics 6th Psychometric Summer School in August 2019. <a href="https://ioe.hse.ru/en/announcements/248134963.html">https://ioe.hse.ru/en/announcements/248134963.html</a><div>The course introduces students to principles and practices behind simplifying data into its component dimensions. <br></div><div>This lecture addresses conceptual issues underlying factor analysis. <br></div><br>