Two drugs were tested to see whether they helped women who had breast cancer without lymph node involvement. The drugs are called TAC (docetaxel, doxorubicin, and cyclophosphamide) and FAC (fluorouracil, doxorubicin, and cyclophosphamide). About half of the 1060 women with breast cancer without lymph node involvement were randomly assigned to TAC, and the other half were assigned to FAC. After 77 months, 473 out of 539 of the women assigned to TAC were alive, and 426 out of 521 women assigned to FAC were alive. (Source: Martin et al., Adjuvant docetaxel for high-risk, node-negative breast cancer, New England Journal of Medicine, vol. 363, no. 23: 2200–10, December 2, 2010)
a. Find both sample percentages of survival, and compare them descriptively.
b. Was this a controlled experiment or an observational study? Explain why. From studies like these, can we conclude a cause-and-effect relationship between the drug type and the survival percentage? Why or why not?