A study from the New England Journal of Medicine- examines the results from a study estimating the association between different contraceptive choices for females, and unintended pregnancies. Here is a description of the study design and analyses, taken from the article abstract: METHODS We designed a large prospective cohort study to promote the use of long-acting reversible contraceptive methods as a means of reducing unintended pregnancies in our region. Participants were provided with reversible contraception of their choice at no cost. We compared the rate of failure of long-acting reversible contraception [intrauterine devices [IUDs] and implants) with other commonly prescribed contra- ceptive methods (oral contraceptive pills, transdermal patch, contraceptive vaginal ring, and depot medroxyprogesterone acetate [DMPA] injection) in the overall co- hort and in groups stratified according to age (less than 21 years of age vs. 21 years or older). The authors used Cox regression to estimate both the unadjusted and adjusted associations between the risk of unintended pregnancy in the study follow-up period, and the type of contraception used by each participant (LARC = "long acting reversible contraception", DPMA = "injection based method" and PPR = "pills, patch or ring"). The reference group for the hazard ratios is LARC. The adjusted hazard ratios are adjusted for age (2 categories), education level (4 categories), and previous number of unintended pregnancies (4 categories). The results are as follows: Table 3. Haand Ratio for Unintended Pregnancy, According to Contraceptive Method and Schooled Characteristic. Unintended Progruncy Total Participant- Variable IN=150 Years Incidence Hazard Ratio p5% CUT Unadjusted Adjusted no /100 participant- years Contraceptive method LARC 21 7655 0.27 1.DO 1.00 OMPA 7 0.22 0.71 0.17-309) 0.70 [0.16-303] PPR 133 2924 4.55 16.05 (10.19-25.29) 21.$4 (13.67-34.85) i Hazard ratios were adjusted for age, educational level, and number of previous unintended pregnancies. 2 Winner B, et al. Effectiveness of Long-Acting Reversible Contraception. New England Joumal of Medicine (2012). 366(21).10. What conclusion can be made based on the results from the unadjusted and adjusted hazard ratios? a. The unadjusted increased risk of unintended pregnancies for women in the PPR group (relative to the other two groups) is mainly attributable to confounding by age and/or education level and/or previous number of unintended pregnancies. b. Education level does not modify the effect of PPR (versus LARC or DMPA) on unintended pregnancies. c. The increased risk of unintended pregnancies for women in the PPR group (relative to the other two groups) remains large, and statistically significant, even after adjustment for age, education level, and previous number of unintended pregnancies. d. The increased risk of unintended pregnancies for women in the PPR group (relative to the other two groups) is not statistically significant after adjustment for age, education level, and previous number of unintended pregnancies