Flashcards in 2 - Sampling Designs Deck (65):
2 approaches for collecting data: 1. 2.
1. Observational study 2. Experimental study
The purpose is to describe and compare existing situations.
The purpose is to study whether a treatment causes a change in the response.
When our goal is to understand cause and effect, ______ are the only source of fully convincing data.
A variable that may explain or cause influences in another variable. AKA independent variable.
Explanatory variable AKA ______.
A variable that is not among the explanatory (independent) variable or response (dependent) variable in a study, and yet may influence the interpretation of relationships among these variables.
Occur when the effects of an explanatory and lurking variable cannot be distinguished from each other.
Why do observational studies often fail to show causality?
Because of confounding (lurking) variables.
The individuals in an experiment are often referred to as _____ if they are human.
The individuals in an experiment are often referred to as _____ if they are not human.
The explanatory (independent) variables in an experiment are often referred to as _____.
Any specific experimental condition applied to the subjects is known as ______.
If an experiment has more than one _____, a _____ is a combination of specific values of each ______.
Treatment, treatment, factor
By assigning subjects to _____, we avoid confounding in experiments.
Another advantage of experiments is that we can study the combined effects of several factors simultaneously, known as ______.
Can produce effects that we were previously unable to predict based at looking at each individual factor alone.
How can you tell what the individuals are?
At what level were participants randomized? Those are the individuals.
How many treatments are there, and what are they?
1. Only physical activity intervention
2. Only nutrition intervention
Does the control count as a treatment?
What is an uncontrolled experiment?
How many factors does this experiment have?
2, normal/vegetarian diet, or unrestricted/restricted salt.
What is being manipulated in an experiment?
Can it be an experiment if the individuals select their own treatment?
No - treatment must be deliberatedly imposed by the researchers.
A sampling survey is an ________ that relies on a ________ sample selected from the entire population at ________.
Observational study; random; a single point in time
Sample surveys are sometimes called ________.
Occurs in a sample survey when some groups in the population are left out of the process of choosing the sample
Undercoverage in a sample survey is a possible cause of ________.
Two sources of bias in sample surveys:
Occurs when an individual cannot be contacted or refuses to cooperate
How does nonresponse in a probability sample differ from opt-in polls that use a voluntary response sample?
Nonresponse: can be improved by increasing the weighting of particular groups
Voluntary response: cannot be improved because we never know what kind of population the respondents represent
Type of bias in a sample survey caused by the behavior of the respondent or the interviewer, or the types of questions being asked.
A woman understating what she weighs is a form of _______.
Confusing or leading questions can induce strong bias, Sometimes this bias results from the order that questions are asked.
An observational study that relies on a random sample drawn from the entire population at one point in time.
A sample survey is sometimes referred to as a _______.
Nonresponse occurs in this type of sample...
An observational study, in which case-subjects are selected based on a defined outcome, and a control group is selected separately to serve as baseline to which the control group is compared.
Is a case-control study observational or experimental?
Case-control studies tend to be _______ (retrospective, prospective).
Cohort studies tend to be _______ (retrospective, prospective).
Subjects sharing a common demographic characteristic are enrolled and observed at regular intervals over an extended period of time.
Which is more prone to confounds: case-control or cohort studies?
Cohort studies - they start with a homogenous group.
Which supports incidence calculations: case-control or cohort studies?
A control treatment that is fake, but otherwise indistinguishable from the experimental group.
When is the placebo affect extra obvious?
When the response variable is pain
Why is randomization used in experiments?
Most experiments are _______.
Randomized comparative experiments
3 principles of experiments:
1. Control the effects of lurking variables on the response, most simply by comparing 2 or more treatments
2. Randomize: use impersonal chance to assign subjects to treatments
3. Use enough subjects in each group to reduce chance variation in the results
Completely randomized design
An experimental design where all the individuals are allocated at random among all the treatments. It is not necessary for the same number of individuals to be assigned to each treatment.
-Can compare any number of treatments
-Can have multiple factors
Simplest statistical design for experiments
Completely randomized design
A group of individuals that are known to be similar in some way that is expected to affect the response to treatments.
The random assignment of individuals is carried out separately within each block.
Blocks are another form of ______.
If you separate people exposed to smoke, from people who are not exposed to smoke, you are using _______.
An experimental design, which compares exactly TWO treatments, either by using a series of individuals, or by using each individual twice. (i.e. giving a person two cuts, treating one, and assessing healing rate).
The assignment of the two treatments within each "pair" must be randomized (i.e. randomize the order).
Comparing treatments given to a set of identical twins is an example of _______.
A matched pairs experimental design
When the same individual is used twice in a matched pairs design, it is often referred to as "_______".
Is randomization in a matched-pairs design independent, or not?
Is assignment to blocks random?
Neither the subject, nor the people who interact with them know which treatment a subject is receiving.
The most serious potential weakness of experiments: _______.
A group of individuals who are similar to each other in a meaningful way.
Are matched pairs or repeated measures a type of block study?
Can the same person in a repeated measure study be considered a block?