Unit 4 Flashcards
the entire group of individuals we
want information about.
population
This collects data from every individual in the population.
census
a subset of individuals in the population from which we
actually collect data.
sample
a study that collects data from a sample that is chosen
to represent a specific population.
sample survey
The design of a statistical study shows
bias if
it is very likely to under or over estimate the value you want to know.
convenience sampling is a bad way to sample because
it will almost always result in bias.
this is a method of sampling whereby you are Choosing individuals from the
population who are easy to reach
convenience sampling
this allows people to choose to be
in the sample by responding to a general invitation.
voluntary response sampling
why is voluntary response sampling a bad way to sample?
People who
self-select to participate in such surveys are usually not
representative of some larger population of interest.
involves using a chance
process to determine which members of a
population are included in the sample.
Random sampling
A —- of size ‘n’ is
chosen in such a way that every group of ‘n’
individuals in the population has an equal
chance to be selected as the sample.
simple random sample (SRS)
When choosing an SRS:
Label, Randomise, Select.
— are groups of individuals in a population who share characteristics
thought to be associated with the variables being measured in a study.
Strata
—- selects a sample by choosing an SRS from each stratum and combining the SRSs into one overall sample.
Stratified random sample
Stratified random sampling works best when the individuals within each
stratum are
similar.
When populations are large and spread out over a wide area, we’d prefer
a method called
cluster sampling.
A —- is a group of individuals in the population that are located near
each other.
cluster
Cluster sampling works best when
the clusters look just like the population but on a smaller scale.
The main reason for using cluster sampling is
for practical reasons, like saving time and money.
Undercoverage occurs when
members of the population are less
likely to be chosen or cannot be chosen in a sample.
Nonresponse occurs when
an individual chosen for the sample can’t be contacted or refuses to participate.
Response bias occurs when
there is a systematic pattern of inaccurate answers to a survey question.
observes individuals and measures
variables of interest but does not attempt to influence the responses.
Observational study
measures an outcome of a study.
response variable
may help explain or predict changes in a response variable
explanatory variable
Confounding occurs when
two variables are associated in
such a way that their effects on a response variable cannot be
distinguished from each other.
An — deliberately
imposes some treatment on
individuals to measure their
responses.
experiment
What is the MAIN difference between an experiment and an observational study?
An experiment administers treatment while an observational study does not.
a treatment that
has no active ingredient, but is
otherwise like other treatments.
Placebo
A specific condition applied to the individuals
in an experiment is called a
treatment
the object to
which a treatment is randomly assigned.
experimental unit
If an experimental unit is a human, it is often called a
subject
a variable that is
manipulated and may cause a change in the
response variable.
factor
The different values of a factor are called
levels
a — is used to provide a
baseline for comparing the effects of other treatments.
control group
The — describes the fact that some
subjects in an experiment will respond favorably
to any treatment, even an inactive treatment.
placebo effect
In a —— experiment, neither the
subjects nor those who interact with them and measure the response variable know which treatment a subject received.
double blind
In a —- experiment, either the subjects don’t know which treatment they are receiving or the people who interact with them and measure the response variable don’t know which subjects are receiving which treatment.
single blind
To create roughly equivalent
groups at the beginning of an
experiment, we use
random assignment
In an experiment, control means
keeping other variables constant for all experimental units.
In an experiment, replication means
using enough experimental units to
distinguish a difference in the effects
of the treatments
What are the four principles of Experimental design?
Comparison, Random assignment, Control, Replication
In a completely randomized design, the experimental units
are assigned to the treatments completely
by chance.
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.
block
the random assignment of
experimental units to treatments is carried out separately
within each block.
randomized block design
a common experimental design for comparing two treatments that uses blocks of size 2. In some designs, two very
similar experimental units are paired and the two treatments are randomly assigned within each pair. In others, each experimental unit receives both
treatments in a random order.
matched pairs
