Quiz 7, Module Cohort
7. Calculation of the rate ratio [Aschengrau & Seage, Chapter 3].
The data collected by your team yield the following information:
- Number of cases among exposed - 74
- Number of cases among unexposed - 120
- Number of exposed person-time of observation (PYO)- 3,675
- Low exposure group- 2,000 PYO's
- Medium exposure group- 1,225 PYO's
- High exposure group- 450 PYO's
- Number of unexposed PYO's- 14,550
- How would you present the data in the 2x2 format?
- Calculate the incidence rate among the exposed. The formula for calculating incidence rate is: (Number of exposed cases during 2-yr time period) / (PYO's among exposed persons during 2-yr time period)
- Calculate the incidence rate among the unexposed.
- Calculate the rate ratio.
- Interpret your findings.
none:
| Disease + | Total PYO's over 2-yr time period | |
|---|---|---|
| Exposed | 74 | 3,675 |
| Unexposed | 120 | 14,550 |
none:
(Number of exposed cases during 2-yr time period) / (PYO's among exposed persons during 2-yr time period)
= 74/3,675
= 0.0200 (or 20 cases per 1,000 PYO's)
The rate of Susser Syndrome among those exposed to SUPERCLEAN (for at least 6 months) is 20 cases per 1,000 PYO's.
none:
(Number of unexposed cases during 2-yr time period) / (PYO's among unexposed persons during 2-yr time period)
= 120/14,550
= 0.0082 (or approximately 8 cases per 1,000 PYO's)
The rate of Susser Syndrome among those unexposed to SUPERCLEAN is 8 cases per 1,000 PYO's.
none:
(Rate of disease among the exposed) / (Rate of disease among the unexposed)
= 0.0200/0.0082
= 2.44
none: Those who were exposed to chemicals involved in the SUPERCLEAN production for at least 6 months have a 2.44 times higher rate of developing Susser Syndrome than those who were not exposed to SUPERCLEAN production.
