Unit Quiz 4 Flashcards
Multistage sample
More than 1 method used
Stratified random sample
gives more precise estimates
Works best when individuals within each stratum are similar w regard to what is being measured and different between strata
What is stratified
Some from all
Clusters
All from some
Inference
Process of drawing conclusions based on sample data
What is in common about convenience and voluntary samples
They are biased
What is SRS
simple
Chosen in such a way that every set of n individuals has an equal chance of being the sample
Under coverage
What’s most common
When some members of the population cannot be chosen in a sample
Non responded
When an individual chosen for the sample cannot be contacted or refuses to participate
Can surveys be non response
No cuz they r voluntary and every individual simply chooses whether they even opt in
Response bias
When people give inaccurate answers to survey questions and there is a systematic pattern of inaccurate
Observational study vs experiment
Observational study observes individuals, and measures variables of interest, but does not attempt to influence the responses, while an experiment deliberately imposes some treatment on individuals to measure their responses 
Confounding
Confounding occurs when two variables are associated in such a way that their effects on response cannot be distinguished from one another 
When asked to identify a possible, confounding variable on AP exam include
How the variable you chose is associated with the explanatory variable, how the variable you chose, affects the response 
Treatment
A specific condition applied to the individuals in experiments
Experimental unit
Experimental units are the smallest collection of individuals which treatments are applied

How is a treatment formed?
It is formed by combining a specific value, called the level of each of the factors(explanatory variables)
P S. Treatments are not explanatory variables, 
Four principles of experimental
 Comparison, random assignment, control, and replication 
Comparison
compare 2+ treatments
Random assignment
Randomly assign experimental units to treatment groups
Control
Keep other variables the same for all grouos
Replication
Use enough units to Eliminate te chance outcomes
Sample is with method as experiment is with
Treatment
Double blind
Neither subjects nor those who interact w them and measure the response know of the subject received a placebo
Statistically significant
An observed effect so large that it would rarely occur by chance
Block
A group of experimental units known to be similar
Randomized block
Random assignments of experimental units to treatments is carried out separately within each block
Matched pairs
Each block consists of a matched pair of experimental units. Sometimes a pair consists of a single unit who receives both treatments in random orders. 
If individuals are randomly selected, you can make an inference about?
The population
If individuals are randomly signed to groups, you can make an inference about ?
Cause-and-effect 
