Question

a tamoxifen study claims that a combination of chemotherapy and the hormone therapy tamoxifen is more effective than tamoxifen alone in preventing breast cancer. in the study, a group of researchers from the u.s. and canada studied 1477 postmenopausal women with early - stage breast cancer. the women were randomly assigned to one of three study groups. the first group of 361 received tamoxifen alone on a daily basis for five years. the second group of 566 received chemotherapy and tamoxifen for six months, and then completed five years of tamoxifen treatment. and the third group of 550 received chemotherapy alone for six months followed by five years of tamoxifen treatment. all 1477 patients knew which treatment they were receiving.

in this study, which is the control group?
○ the 1477 postmenopausal women
○ the third group of 550 that received chemotherapy alone for 6 months and then tamoxifen for 5 years
○ the second group of 566 that received tamoxifen and chemotherapy concurrently for 6 months
○ the first group of 361 that received tamoxifen alone
○ there is no control group.

this study is
○ double - blind
○ not blind,
○ blind, but not double - blind
○ not an experiment
○ none of the above

Explanation:

First Sub - Question (Control Group)

A control group in an experiment is a group that is not exposed to the independent variable (the treatment being tested, here the combination with chemotherapy) and is used for comparison. The first group received only tamoxifen, while the other groups received chemotherapy in addition (or alone first then tamoxifen). The 1477 women are the total sample, not a control group. The second and third groups have chemotherapy, so they are experimental groups. Since all patients knew their treatment, but for the control group definition, the first group (tamoxifen alone) is the control as it's the base treatment without the added chemotherapy (the variable being tested in the other groups). Wait, no - actually, the study is testing if combination with chemotherapy is better than tamoxifen alone. So the control group should be the one with the standard treatment (tamoxifen alone) to compare against the groups with chemotherapy. But also, we need to check the blinding. Wait, the first sub - question: the options are:

• the 1477 postmenopausal women: This is the total sample, not a control group.
• the third group: received chemotherapy alone then tamoxifen, so has chemotherapy, not a control.
• the second group: received chemotherapy and tamoxifen, has chemotherapy, not a control.
• the first group: received tamoxifen alone. In an experiment testing the effect of adding chemotherapy to tamoxifen, the control group is the one with the original treatment (tamoxifen alone) to see if the addition (chemotherapy) has an effect. But wait, also, the last option is "There is no control group." Wait, but in a controlled experiment, we need a control. However, let's re - examine: the study has three groups: tamoxifen alone, chemo + tamoxifen, chemo alone then tamoxifen. The research question is about combination of chemo and tamoxifen vs tamoxifen alone. So the control group for that comparison would be tamoxifen alone (first group). But wait, maybe the study is not a controlled experiment? No, it's an experiment with random assignment. Wait, but the options: let's check each. The first group: tamoxifen alone. The other groups have chemotherapy. So the control group (for the comparison of chemo + tamoxifen vs tamoxifen alone) is the first group. But wait, the last option is "There is no control group." Wait, maybe because all groups have tamoxifen? Wait, no: first group: tamoxifen alone. Second: chemo + tamoxifen (6 months) then tamoxifen. Third: chemo alone (6 months) then tamoxifen. So the first group is tamoxifen alone, the second has chemo + tamoxifen, the third has chemo then tamoxifen. The research question is "a combination of chemotherapy and the hormone therapy tamoxifen is more effective than tamoxifen alone". So the control group should be the one with tamoxifen alone (first group) to compare the combination (second group) against. But wait, the third group has chemo alone then tamoxifen. So maybe the study has two experimental groups (second and third) and one control (first)? But let's check the options. The options are:

1. the 1477 postmenopausal women: No, that's the sample.
2. the third group: No, has chemo.
3. the second group: No, has chemo.
4. the first group: Yes, because it's the group with the standard treatment (tamoxifen alone) against which the groups with chemo are compared.
5. There is no control group: No, because the first group is the control.

Wait, but maybe I'm wrong. Wait, in a control group, we want to have a group that is as similar as possible to the experimental groups except for the independent variable. The indep…

A blind study is where participants don't know their treatment, a double - blind is where both participants and researchers don't know. The problem states "All 1477 patients knew which treatment they were receiving." So it's not blind (since patients know), so it's not blind, not double - blind. The study is an experiment (random assignment to groups), so the option "not blind" is correct.

Answer:

the first group of 361 that received tamoxifen alone

Second Sub - Question (Study Type - Blinding)