Question

A researcher followed a cohort for 10 years after the Aliso canyon gas spill. The researcher interviewed 290 residents. 140 residents lived within a 2 mile radius of the leak and were classified as exposed and 150 residents lived more than 5 miles away and were considered unexposed. In total 120 of the 140 residents exposed to the gas developed respiratory problems and 10 of the 150 not exposed to the gas developed respiratory problems.

	Respiratory Problems	No Respiratory Problems	Total
Exposed to Gas
Not Exposed to Gas
Total

Question	Answer
1. What was the incidence of Respiratory Problems per 1000 in the exposed group?
Interpretation 1:
2. What was the incidence of Respiratory Problems per 1000 in the un-exposed group?
Interpretation 2:
3. Calculate a relative risk or risk ratio for this study and interpret this number.
Interpretation 3:
4. Calculate the Attributable Risk Percent/ Etiologic Fraction Percent and interpret this number.
Interpretation 4:

Answer 1

Result:

A researcher followed a cohort for 10 years after the Aliso canyon gas spill. The researcher interviewed 290 residents. 140 residents lived within a 2 mile radius of the leak and were classified as exposed and 150 residents lived more than 5 miles away and were considered unexposed. In total 120 of the 140 residents exposed to the gas developed respiratory problems and 10 of the 150 not exposed to the gas developed respiratory problems.

	Respiratory Problems	No Respiratory Problems	Total
Exposed to Gas	120	20	140
Not Exposed to Gas	10	140	150
Total	130	160	290

Question	Answer
1. What was the incidence of Respiratory Problems per 1000 in the exposed group? (120/140)*1000	857.143
Interpretation 1: 857 out of 1000 residents developed Respiratory Problems who exposed to Gas.
2. What was the incidence of Respiratory Problems per 1000 in the un-exposed group? (10/150)*1000	66.6667
Interpretation 2: 67 out of 1000 residents developed Respiratory Problems who not exposed to Gas.
3. Calculate a relative risk or risk ratio for this study and interpret this number. RR = (120/140)/(10/150)	12.8571
Interpretation 3: residents exposed to the gas are 12.9 times more likely to develop respiratory problems than not exposed to gas.
4. Calculate the Attributable Risk Percent/ Etiologic Fraction Percent and interpret this number. ((120/140)-(10/150))*100	79.05
Interpretation 4: This means 79.05% of respiratory problems are caused by exposed to the gas.