It's widely believed that regular mammogram screening may detect breast cancer early, resulting in fewer deaths from that disease. One study that investigated this issue over a period of 18 years was published during the 1970s. Among 30,565 women who had never had mammograms, 196 died of breast cancer, while only 153 of 30,131 who had undergone screening died of breast cancer.
a) Do these results suggest that mammograms may be an effective screening tool to reduce breast cancer deaths?
b) If your conclusion is incorrect, what type of error have you committed?