1 Subjects: “...bivariate probability density function...”

2 Subjects: “...probability density function...”

3 Subjects: “...probability density function...”

4 Subjects: “...probability density functions...”

5 Subjects: “...probability density function...”

6 Subjects: “...probability density function...”

7 Subjects: “...probability density function of the Gaussian distribution...”

8 Subjects: “...probability density function...”

9 Subjects: “...probability density function...”

10 Subjects: “...probability density functions...”