One possible design to study the benefits to infants of breast milk would be a very large observational study. Another possibility would be a blind experiment wherein a very small group of women are provided daily with bottles of breast milk to feed their infants, while another small group is provided with bottles of formula. If differences between breast-fed and bottle-fed infants are, in fact, rather subtle, which study would be more likely to fail to find clear evidence of breast milk's benefits?