Certain types of diseases tend to occur in clusters. In particular, persons affected with AIDS, syphilis, and tuberculosis may have some common characteristics and associations which increase their chances of contracting these diseases. The following table lists the number of reported cases by state in 2001.
| State |
AIDS |
Syphills |
Tuber |
State |
AIDS |
| AL |
438 |
720 |
265 |
MT |
15 |
| AK |
18 |
9 |
54 |
NE |
74 |
| AZ |
540 |
1147 |
289 |
NV |
252 |
| AR |
199 |
239 |
162 |
NH |
40 |
| CA |
4315 |
3050 |
3332 |
NJ |
1756 |
| CO |
288 |
149 |
138 |
NM |
143 |
| CT |
584 |
165 |
121 |
NY |
7476 |
| DE |
248 |
79 |
33 |
NC |
942 |
| DC |
870 |
459 |
74 |
ND |
3 |
| FL |
5138 |
2914 |
1145 |
OH |
581 |
| GA |
1745 |
1985 |
575 |
OK |
243 |
| HI |
124 |
41 |
151 |
OR |
259 |
| ID |
19 |
11 |
9 |
PA |
1840 |
| IL |
1323 |
1541 |
707 |
HI |
103 |
| IN |
378 |
529 |
115 |
SC |
729 |
| IA |
90 |
44 |
43 |
SD |
25 |
| KS |
98 |
88 |
63 |
TN |
602 |
| KY |
333 |
191 |
152 |
TX |
2892 |
| LA |
861 |
793 |
294 |
UT |
124 |
| ME |
48 |
16 |
20 |
VT |
25 |
| MD |
1860 |
937 |
262 |
VA |
951 |
| MA |
765 |
446 |
270 |
WA |
532 |
| MI |
548 |
1147 |
330 |
WV |
100 |
| MN |
157 |
132 |
239 |
WI |
193 |
| MS |
418 |
653 |
154 |
WY |
5 |
| MO |
445 |
174 |
157 |
All States |
41,868 |
a. Construct a scatterplot of the number of AIDS cases versus the number of syphilis cases.
b. Compute the correlation between the number of AIDS cases and the number of syphilis cases.
c. Does the value of the correlation coefficient reflect the degree of association shown in the scatterplot?
d. Why do you think there may be a correlation between these two diseases?