Studied by 7 people
Observational Study
Observing with no treatment
Experiment
Imposing treatment
What does a larger sample size do?
Reduces variability when the sampling design is NOT flawed
Nonresponse bias
Selected people do not respond
Undercoverage Bias
Systematically excluding people from being able to be selected
Response Bias
Providing inaccurate responses (on purpose or by accident)
Wording Bias
Confusing wording or question is slanted towards a particular response
Stratified Random Sample
Division of a population into separate groups (strata) based on shared attributes (homogeneous grouping), SRS is done to select people within the strata, and those units are combined to form the sample.
Experimental unit
Used when an experiment is not performed on humans, but on animals or objects
Subjects
Used when an experiment is done on humans
Confounding Variable
Variable that is related to the explanatory variable and influences the response variable, makes it challenging to determine cause and effect
What should a well-designed experiment include?
Comparisons of at least 2 treatment groups (one could be a control)
Random assignment of treatments to experimental units
Replication: enough experimental units in each treatment group to be able to detect a difference
Control of a potential confounding variables where appropriate
Bias
Systematic tendency to overestimate or underestimate the true population parameter
Randomized Block Design
Treatments are assigned completely at random within each block. For each block individuals are similar to one another with respect to at least one blocking variable
Benefits of Block Design
reduce variability of results within each treatment group and eliminate possibility of the blocking variable as the confounding variable
Can results be generalized to a larger population
Yes, but only to the population that the subjects/units were randomly selected from
What are two poor sampling methods?
Convenience sampling and voluntary response sampling (neither uses chance to select individuals)
Simple Random Sample (SRS)
A sample in which every group of a given size has an equal chance of being chosen
How to obtain an SRS
number individuals, use a random # generator/table/draw from hat to select which to include in study (excluding repeats)
Control Group
collection of experimental units that are either not given a treatment of interest or given a treatment with an inactive substance (placebo).
Purpose of control group
Provide a baseline for comparison
Explanatory Variable
a variable whose levels are intentionally maipulated
Response Variable
an outcome from the experimental units that is measured after the treatments have been administered
Completely Randomized Design
Treatments are randomly assigned to experimental units, tends to create roughly equivalent groups so that differences in responses can be attributed to the treatments
Matched Pairs Design
Special randomized block design, each pair receives both treatments by randomly assigning one treatment to one member and the remaining to the other, or both subjects get both treatment
Systematic Random Sample
members from a population are selected according to a random starting point and a fixed, periodic interval, (like every 5th person)
Note
Flashcard