stuff 2 Flashcards
Why use a control group?
A control group gives the researchers a comparison group to be used to evaluate the effectiveness of the treatments). (context) It allows the researchers to measure the effect of the treatment (context) compared to no treatment at all.
Confounding
Two variables are confounded if it cannot be determined which variable is causing the change in the response variable. For example, if people who take vitamins on their own have less cancer, we cannot say for sure that the vitamins are causing the reduction in cancer. It could be other characteristics of vitamin takers, such as diet or exercise.
Experimental Designs
CRD (Completely Randomized Design) - Units are allocated at random among all treatments RBD (Randomized Block Design) -Units are put into homogeneous blocks and randomly assigned to treatments within each block. Matched Pairs - A form of blocking in which each subject receives both treatments in a random order or subjects are matched in pairs with one subject in each pair receiving each treatment, determined at random.
Blinding
When the subjects in an experiment don’t know which treatment they are receiving, they are blind. If the people interacting with the subjects and measuring the response variable don’t know which subjects received which treatments, they are blind. If both groups are blind, the study is double-blind.
Scope of Inference: Generalizing to a Larger Population
We can generalize the results of a study to a larger population if we used a random sample from that population.
Benefit of Blocking
Blocking helps account for the variability in the response variable (context) that is caused by the blocking variable (context). If there really is a difference in the effectiveness of the treatments, using an appropriate blocking variable will increase power (probability of finding convincing evidence that the treatments are not equally effective).
Scope of Inference: Cause-and-Effect
We can make a cause-and-effect conclusion if we randomly assign treatments to experimental units in an experiment. Otherwise, Association is NOT Causation!
Interpreting Probability
The probability of an event is the proportion of times the event would occur in a very large number of repetitions. Probability is a long-term relative frequency
Conducting a Simulation
State: Ask a question about some chance process. Plan: Describe how to use a random device to simulate one trial of the process and indicate what will be recorded at the end of each trial. Do: Do many trials. Conclude: Answer the question of interest.
Law of Large Numbers
Law of Large Numbers says that if we observe many repetitions of a chance process, the observed proportion of times that an event occurs approaches a single value, called the probability of that event.
