Ignoring losses to follow-up (which you may do), each woman in the study had baseline ferritin level and a 12-month ferritin level, so each woman had a change in ferritin level from baseline to 12 months. 56 women were treated with COC and 56 were treated with LNG-IUS. What 2 numbers should the authors have compared? The hint is meant to indicate that the correct comparison would yield a p-value of < 0.001.