Given the preceding data, assess whether pollution level acts as a trigger effect in causing heart attack?

Environmental Health

Some previous studies have shown that mortality rates are higher on days with high pollution levels. In a follow-up on this observation, a group of 50 nonfatal heart attack cases were ascertained over a 1-year period. For each case, the level of pollution (total suspended particulates) was measured on the day of the heart attack (index date) and also 1 month before the heart attack (control date).

The results shown in Table 5.4 were obtained:

Table 5.4: Comparison of pollution levels on index date vs. control date

______________________________________________ n

Pollution level on index date > pollution level 

on control date ………………………….……............ 30

Pollution level on control date > pollution level

on index date …………………………............……… 15

Pollution level the same on ………………......…….. 

both days ……………………..………………................. 5

Total …………………………..………………................. 50