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Stat 212
Exam 1 (Chapter 4)
33
Mathematics
Undergraduate 2
09/29/2009

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Cards

Term
Population versus sample
Definition
  • Population: all subjects of interest
    • we use statistics to learn about population and the entire group of interest
  • Sample: Subset of the population
    • Data collected for sample because we cannot measure all subjects in population
Term
Observational study
Definition
  • Researcher observes response/explanatory variable.
  • Nothing done to subjects
Term
Experimental study
Definition
  • assigns subjects to experimental conditions and observing outcomes based on response variable
  • randomized experiments = subjects randomly assigned to treatmetns
  • randomization reduce potential for lurking variable
  • gives more control over outside influences
  • only experiment can establish cause/effect
  • not always possible due to time/ethical factors
Term
Sampling Frame
Definition
  • list of subjects in population from which sample is taken
  • ideally lists the entire population of interest
Term
Sampling Design
Definition
  • determines how sample is selected
  • ideally gives each subject equal change of being selected to be in sample
Term
Simple Random Sample
Definition
  • each possible sample of n size has same chance of being selected
Term
How to Use Random Number Table
Definition
  • Number subjects in sampling frame using numbers of same length
  • select numbers of same length from table of random numbers
  • Include in the sample those subjects having numbers equal to the random numbers selected
Term
Margin of Error
Definition
  • tell us how well the sample estimate predicts the population percentage
  • Simple random sample of n subjects will have margine of error of 1/(√n) *100%
Term

Convenience Samples (Poor ways to Sample)

 

Volunteer Sample

Definition
  • Convenience sample: type of survey sample that is easy to obtain
    • Unlikely to be representative of population
    • Often severe biases result from sample
    • Results apply only to observed subjects
  • Volunteer Sample: Most common form of convenience sample
    • Subjects volunteer for sample
    • volunteers do not tend to be representative of entire population
Term
Undercovage
Definition
  • Having sampling frame that does not represent some parts of population
Term
Sampling bias
Definition
  • Bias resulting form sampling method
    • ex. nonrandom samples or undercoverage
Term
Nonresponse bias
Definition
  • Occurs when some sampled subjects cannot be reached or refuse to participate or fail to answer some question
Term
Response bias
Definition
  • Occurs when subject gives an incorrect response or question is misleading

Large sample does not guarantee unbiased sample

Term
Key pars of a sample survey
Definition
  • ID population of all subjects of interest
  • Construct sampling frame that attempts to list all subjects in the population
  • Use random sampling design to select n subjects from sampling frame
  • Be cautious of sampling bias due to nonrandom samples
Term
Experimental units
Definition
  • Subjects of an experiment
  • entities that we measure in an experiment
Term
Treatment
Definition
  • specific experimental condition imposed on subjects of the study
  • Treatmetns correspond to assigned values of explanatory variable
Term
Explanatory variable
Definition
  • Defiens groups to be compared with respect to values on response variable
Term
Response variable
Definition
  • Outcome measured on subjects to reveal effect of the treatments
Term
4 Components of good experiment
Definition
  • Control/comparison group
  • Randomization
  • Replication
  • Blinding the Study
Term
Control/ Comparison group
Definition
  • Allows researcher to analyze effectiveness of primary treatment
  • Control group typically receives placebo
Term
Randomization
Definition
  • Eliminates possible research bias
  • Balances comparison groups on known as well as on unknown variables
Term
Replication
Definition
  • process of assigning several experimental units to each treatment
  • allows us to attribute observed effects to the treatments rather than ordinary variability
Term
Blinding the study
Definition
  • subjects unaware to treatment received
  • double blind experiment controls response bias from respondent and experimenter
Term
Statistical significance
Definition
  • observed differences in experiment is larger than what would be expected just by chance
Term
Stratified Random Sampling
Definition
  • Divide populations into separate groups called strata
  • Select simple random sample from each stratum
  • Combine samples from all strata to form complete sample
  • Pro:
    • can include in sample enough subjects in each stratum you want to evaluate
  • Cons:
    • must have sampling frame and know into which stratum each subject belongs
Term
Cluster random sampling
Definition
  • Divide population into large number of clusters (ex. city blocks)
  • select simple random sample of the clusters
  • use subjects in clusters as sample
  • Preferable when:
    • reliable sampling frame is unavailable
    • Cost of selecting SRS is excessive
  • Disadvantage
    • need larger sample size than SRS in order to achieve particular margine of error
Term
Sample Survey
Definition
  • Attempts to take a cross section of a population at the current time
Term
Retrospective Study
Definition
  • Observation study
  • looks into past
  • Case-control study
Term
Prospective Study
Definition
  • Observational study
  • follows subjects into the future
Term
Multifactor experiment
Definition
  • uses single experiment to analyze effects of 2 or more explanatory variables on the response
  • Categorical explanatory varibles in experiments are called factors
Term
Matched Pairs Design
Definition
  • subjecst receiving 2 treatments are somehow matched
  • ex. same person, husband wife, 2 plots in same field
Term
Crossover design
Definition
  • Same individual used for 2 treatments
Term
Randomized block design
Definition
  • Block = set of experimental units w/ one or more matched characteristics
  • Randomized block design = random assignment of experimental units to treatments is carried out separately w/i each block. 
  • elimiinates variability in response due to blocking variable
  • matched pairs design = special case of RBD
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