Systolic Blood Pressure
The frequency distribution for the systolic blood pressure readings (in millimeters of mercury, mm Hg) of 200 randomly selected college students is shown here. Construct a percentile graph.
A |
B
Frequency |
C Cumulative frequency |
D Cumulative percent |
89.5–104.5 | 24 | ||
104.5–119.5 | 62 | ||
119.5–134.5 | 72 | ||
134.5–149.5 | 26 | ||
149.5–164.5 | 12 | ||
164.5–179.5 | 4 | ||
200 |
Step 1 Find the cumulative frequencies and place them in column C.
Step 2 Find the cumulative percentages and place them in column D. To do this step, use the formula
Cumulative % =\frac{\text{cumulative frequency}}{n} · 100
For the first class,
Cumulative % =\frac{24}{200} · 100 = 12%
The completed table is shown here.
Step 3 Graph the data, using class boundaries for the x axis and the percentages for the y axis, as shown in Figure 3–6.
A Class boundaries |
B
Frequency |
C Cumulative frequency |
D Cumulative percent |
89.5–104.5 | 24 | 24 | 12 |
104.5–119.5 | 62 | 86 | 43 |
119.5–134.5 | 72 | 158 | 79 |
134.5–149.5 | 26 | 184 | 92 |
149.5–164.5 | 12 | 196 | 98 |
164.5–179.5 | 4 | 200 | 100 |
200 |