section 1.4: experiments Flashcards
what is natural variation?
when we do an experiment, the results are going to be slightly different each time
what are experiments?
studies where the researchers assign treatments to cases
what is a randomized experiment?
assignment to the groups is randomized
what is controlling?
researchers assign treatments to cases, and they do their best to control any other differences in the groups, keep as many other variables the same as we can
what is randomization and why is it done?
researchers randomize patients into treatment groups to account for variables that cannot be controlled
what is replication and why is it done?
the more cases researchers observe, the more accurately they can estimate the effect of the explanatory variable on the response
what is blocking and why is it done?
Researchers sometimes know or suspect that variables, other than the treatment, influence the response. Under these circumstances, they may first group individuals based on this variable into blocks and then randomize cases within each block to the treatment groups
what is a blind experiment?
when researchers keep the patients uninformed about their treatment
what is a double-blind experiment?
doctors or researchers who interact with patients are, just like the patients, unaware of who is or is not receiving the treatment
what is a sham surgery?
patient does undergo surgery, but the patient does not receive the full treatment, though they will still get a placebo effect
what are the four principles of a randomized experiment?
controlling, randomization, replication, blocking
Look back to the study in Section 1.1 where researchers were testing whether stents were effective at reducing strokes in at-risk patients.
Is this a randomized experiment?
Yes, groups were assigned randomly and there was a treatment and control group
was the section 1.1 study blind?
No, people had surgery to get the stent, and those who didn’t get the stent didn’t get surgery, so subjects knew whether or not they received treatment
was the section 1.1 study double-blind?
no, patients knew which group they were in
if the study isn’t blind, it can’t be double blind
what is an example of controlling?
when patients take a drug in pill form, some
patients take the pill with only a sip of water while others may have it with an entire glass of water. To control for the effect
of water consumption, a doctor may ask all patients to drink a 12 ounce glass of water with the pill.
what is an example of replication?
In a single study, we replicate by collecting a sufficiently large sample. Additionally, a group of scientists may replicate an
entire study to verify an earlier finding.
what is an example of blocking?
if we are looking at the effect of a drug on heart attacks, we might first split patients in the study into low-risk and high-risk
blocks, then randomly assign half the patients from each block to the control group and the other half to the treatment group, as shown in Figure 1.16. This strategy ensures each treatment
group has an equal number of low-risk and high-risk patients.
of the four principles, which three are the most important to incorporate in every study?
replication, controlling, and randomization
what type of experiment is the gold standard for data collection?
randomized experiment
how to we make experiments truly blind?
by using a placebo instead of giving the control group nothing
what is the main difference between a sham surgery and no treatment?
sham surgery tends to create
additional risk, while withholding a treatment only maintains a person’s risk.
what is an explanatory variable?
it is the variable that is manipulated in an experiment. the independent variable. it explains why a change occurred in an experiment.
