Sampling
Uses subjects that are readily available
What is a Convenience Sampling?
A radio talk show host asks listeners to call in with their opinions of making wearing masks in public space mandatory.
An example of Voluntary Response Bias
Observes individuals and measures variables of interest but does not attempt to influence the responses
What is an Observational Study?
An experimental design diagram always starts with the...
experimental units
Unmeasured variables that influence the relationship between the explanatory and response variables.
What is Confounding variables?
A sample obtained by allowing subjects to decide whether or not to respond
What is a Voluntary Response Sample?
Because they are generally fearful of government intrusion, many immigrants from Latin America did not return their census questionnaire during the 1990 census.
What is Non- response bias?
Deliberately imposes some treatment on individuals to measure their response.
What is an Experiment?
The most important element of any experiment and it must be incorporated either in the selection process of experimental units and/or the distribution of experimental units into treatments and control groups.
What is Randomization?
To earn more, get married? Data show that men who are married, and also divorced or widowed men, earn quite a bit more than men who have never been married.
What is the confounding variable?
Age
Consists of individuals from the population chosen in such a way that every set of individuals has an equal chance in the sample selected
What is a Simple Random Sample (SRS)?
A job applicant is asked to take a personality test during the recruitment process. One of the questions is “Do you like meeting new people?” This question is most likely to suffer from what type of bias?
Response Bias (lying)
A medical team examines the records of 5 large hospitals and compares the survival times of those cancer patients who had surgery versus those who had chemotherapy.
Observational Study
Treated identically in all respects to the group receiving the treatment except that the members of THIS group do not receive the treatment.
Considered the 'baseline' of an experiment.
What is the Control Group?
Type of experimental design where groups of experimental units known to be similar in some specific characteristic are made before randomly assigning treatments.
What is block design?
Divide the population into groups of similar individuals, then select an SRS within each group. Combine the SRS from each group to form your full sample.
What is a Stratified Random Sampling?
A company wants to know the opinion of a rural community on a proposed ballot initiative. Half of the community does not have internet access, so the company sends emails to the 380 members that do have internet access. Of those surveyed, 372 of the community members responded to the survey. Which of the following is the most significant source of bias in the survey?
What is undercoverage bias?
In gym class, the effect of exercise on blood pressure is studied by requiring that half of the students walk a mile each day while the other students run a mile each day,
Experiment
A group of middle school students want to know if they can use height to predict age. They take a random sample of 50 people at their school, both students and teachers, and record each individual’s height and age. Identify the explanatory and response variables.
Explanatory: Height
Response: Age
For an experiment, the individuals to be a part of it were randomly chosen but the groups were not randomly assigned. Can I make an inference that generalizes on the population based on this information?
Yes, I can generalize my results to a population but I cannot establish causation.
Divide the population into sections, then randomly choose a few of those sections. Every member of the selected sections becomes your sample.
What is a Cluster Sample?
A researcher wants to survey the opinions of university students but only collects responses from those registered with the student government association.
Undercoverage bias
The relationship between weights of bears and their lengths is studied by measuring bears that have been anesthetized
Observational Study
An experimental study wants to see the effect of a new diet. There are 100 experimental units and each subject is paired with someone of a similar weight and height. What type of experimental design is used here?
Matched pairs design.
The use of enough subjects in each group so that the differences in effects from the treatments can be distinguished from random chance differences between the groups.
What is replication?