These are different characteristics that the study participants have. This could be referring to the average age of each group, their BMI, the number of embryos transferred, etc. Itโs essentially all the characteristics of patients that arenโt being studied, but might have an impact on the results. Ideally, all of these different characteristics should be balanced (same age, same BMI, etc.) so what weโre testing isnโt being influenced by these characteristics.
Letโs suppose weโre looking at the pregnancy rate after transferring 1 vs 2 embryos.
Letโs say the two groups have the same baseline characteristics โ same BMI, same diagnosis, same AMH levels, etc. Everything is the same, except for their age. The women in the 2 embryo group are younger.
Because younger women generally have a higher pregnancy rate than older women, we need to be careful when we interpret the results. If we find that the 2 embryo group has a higher birth rate โ is this because they transferred 2 embryos, or because theyโre younger?
This data can be โstatistically adjustedโ to control for age โ by grouping all the women who have the same age together and then seeing what impact 2 vs 1 embryo has on pregnancy outcomes.