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Observational Study
observes individuals and measures variables of interest but does not attempt to influence the responses, can be generalized to a population if there's random selection
Standard Deviation
a measure of how dispersed the data is in relation to the mean.
Response Variable
the variable that is measured or observed (output)
Explanatory Variable
Specific conditions applied to the subject (input)
Experiment
A research method in which an investigator deliberately imposes some treatment on individuals to measure their responses, when the goal is to understand causality (the relationship between cause and effect)
Experimental Unit
the smallest collection of individuals to which treatments are applied (Humans are called subjects)
Treatment
a specific condition applied to the individuals in an experiment
Confounding
occurs when two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other
Completely Randomized Design
the treatments are assigned to all the experimental units completely by chance
double-blind experiment
neither the subjects nor those who interact with them and measure the response variable know which treatment a subject received
Single-blind
Subjects know which treatment they will be receiving, but experimenters do not (or vice versa)
statistically significant
an observed effect so large that it would rarely occur by chance
Randomized Block Design
the random assignment of experimental units to treatments is carried out separately within each block
Block
a group of experimental units that are known before the experiment to be similar in some way that is expected to affect the response to the treatments
matched pairs design
in a matched pair design, subjects are paired by matching common important attributes
Types of Experiments
Completely Randomized Design, Randomized Block Design, and Matched Pair Design
Placebo
A treatment that has no active ingredient, but is otherwise like other treatments
Factor
an explanatory variable that's manipulated and may cause a change in the response variable
Levels
the different values of a factor
control group
A group used to provide a baseline for comparing the effects of other treatments
Placebo effect
some subjects in an experiment will respond favorably to any treatment
Control
keeping other variables constant for all experimental units
Replication
giving each treatment to enough experimental units so that a difference in the effects of the treatments can be distinguished from chance variation due to the random assignments
population
the entire group of individuals about which we want information
census
collects data from every individual in the population
sample
a subset of individuals in the population from which we collect data
sample survey
a study that collects data from a sample to learn about the population from which the sample was selected
convenience sampling
selects individuals from the population who are easy to reach
Bias
likely to underestimate or very likely to overestimate the value you want to know
Voluntary Response Sampling
Allows people to choose to be in the sample by responding to a general invitation This may lead to bias because often in voluntary response sampling, only people who feel strongly towards the subject often reply/participate
Random Sampling
involves using a chance process to determine which members of a population are included in the sample
SRS
chosen in such a way that every group of n individuals in the population has an equal chance to be selected as the sample
Sampling without replacement
an individual from a population can be selected only once
sampling with replacement
an individual from a population can be selected more than once
strata
groups of individuals in a population who share characteristics thought to be associated with the variables being measured in a study
stratified random sampling
selects a sample by choosing an SRS from each stratum and combining the SRSs into one overall sample
cluster
a group of individuals in the population that are located near each other
cluster sampling
selects a sample by randomly choosing clusters and including each member of the selected clusters in the sample
Systematic random sampling
selects a sample from an ordered arrangement of the population by randomly selecting one of the first k individuals and choosing every kth individual thereafter
under coverage
occurs when some members of the population are less likely to be chosen as a sample
non response
where an individual chosen for the sample can't be contacted or refuses to participate
response bias
when there is a systematic pattern of inaccurate answers to a survey question
wording of questions
confusing or leading questions can introduce strong bias
