– Two random variables recorded from each sampling unit • Abundance of a plant species and soil pH from each of several sampled plots • Blood pressure and body weight from patients – Multivariate data – when more than two variables recorded from one sampling unit. – During correlation analysis, the relationship between two continuous variables is described. – Use that relationship as a basis for prediction.
Pharmaceutical Biostatistics: Correlation & Regression
• A graph in which the paired (x,y) sample data are plotted with horizontal x-axis and a vertical y-axis. • Each individual (x,y) pair is plotted as a single point. • Scatter plots are created by setting up two continuous axes, then creating a dot for every pair of observations.
Pharmaceutical Biostatistics: Correlation & Regression
n Weight and systolic blood pressure of 10
patients.
Weight (kg)
67
69
85
83
74
81
97
92
114
85
SBP (mmHg)
120
125
140
160
130
180
150
140
200
130
Pharmaceutical Biostatistics: Correlation & Regression
Weight (kg) SBP (mmHg)
67
69
85
83
74
81
97
92
114
85
120
125
140
160
130
180
150
140
200
130
SBP(mmHg)
220 200 180 160 140 120 100
wt (kg)
80 60
70
80
90
100
Pharmaceutical Biostatistics: Correlation & Regression
110
120
Perfect positive correlation (+1.00)
Pharmaceutical Biostatistics: Correlation & Regression
Perfect negative correlation (-1.00)
No relationship (0.00)
Pharmaceutical Biostatistics: Correlation & Regression