Question

Anecdotal evidence has suggested that a specific type of oral contraceptive pill puts women at greater risk for blood clots. Researchers decide to examine this scientifically by starting a prospective cohort study. They enroll women between the ages of 15 and 45 who are using this type of oral contraceptive pill as well as similar women who are not using this contraceptive pill. At baseline none of the women had ever had a blood clot. Then they follow these study participants for 5 years, following up with them once a year to determine if they suffered from a blood clot. At the end of 5 years the researchers report the following information: Out of a total of 6000 women that were taking the oral contraceptive of interest, 575 had reported blood clots. Of the 7000 women not taking the oral contraceptive of interest, 250 reported a blood clot.

A. Create an appropriate 2x2 table for this data. (Fill out the chart)

	Blood Clot	No Blood Clot
Oral Contraceptive (Exposure)
No Oral Contraceptive (No Exposure)

B. Calculate the relative risk of having a blood clot for women taking the oral contraceptive pill in question compared to those not taking the contraceptive pill in question (show steps).

C. Assume that this RR is significant. What does this RR mean (be specific using the context of this study)?

  

Answer 1

A. Create an appropriate 2x2 table for this data. (Fill out the chart)

	Blood clot	No Blood clot	Total
Taking Contraceptive	575 (a)	5425 (b)	6000
Not taking	250 (c)	6750 (d)	7000
Total	825	12175	13000

6000 and 7000 are the row totals.

575 are out of 6000 taking contraceptive who reported blood clot. So this mean this number represent exposed and blood clot.

Similarly 250 are out of 7000 not taking contraceptive who reported blood clot. So this mean this number represent unexposed and blood clot.

The rest of the numbers can be found by taking totals and differences.

B. Calculate the relative risk of having a blood clot for women taking the oral contraceptive pill in question compared to those not taking the contraceptive pill in question (show steps).

Relative risk compares probability of having blood clot when exposed and the probability of having blood clot when unexposed.

Relative Risk = (a/(a+b) / (c(c+d))

=

C. Assume that this RR is significant. What does this RR mean (be specific using the context of this study)?

So this means that the numerator is greater than denominator almost 2 and half times more.

Therefore the probability that having blood clot with taking pills is 2 and hlf times more than probability that having blood clot without taking pills.