Other advantages of RCTs include a low risk of selection bias and an unbiased distribution of confounders. RCTs may be blinded and blinding reduces the risk of performance and measurement bias. Some of the limitations are that RCTs might be expensive, time consuming, and do not allow for a lifetime of follow- up. For some interventions (e.g. investigation of the effects of breastfeeding), RCTs may be unethical [7].