Chapter 5 ~ Producing Data Flashcards
observational study
observes individuals and measures variables of interest but does not attempt to influence the response
experiment
deliberately imposes some treatment on individuals in order to observe their responses. An experiment can help eliminate (or at least try to minimise the effects of) lurking variables.
population
the entire group of individuals that we want information about
sample
the part of the population which we actually examine in order to gather info
sampling
studying a part in order to gain information about the whole
census
attempts to contact every individual in the entire population
voluntary response sample
consists of people who choose to be part of a sample by responding to a general appeal
biased
convenience sample
involves choosing the most convenient individuals from the population for your sample
biased
simple random sample (SRS)
a sample of size n is selected in such a way if every individual in the population has an equal chance of being selected and every subset of n individuals has an equal chance of being selected for the sample
stratified random sample
includes the following steps: divide the population into groups of similar individuals called strata, choose a separate SRS from each stratum, and then combine all of those individuals chosen from all of the strata to make up the full sample.
NOT an SRS
cluster sample
divides the population into groups (or clusters), then randomly selects some of these clusters (completely ignoring the others). All of the individuals from the chosen clusters are selected to be in the sample.
multistage sample design
selects successively smaller groups within the population in stages, resulting in a sample consisting of clusters of individuals. Each stage may employ an SRS
systematic sample
choosing every nth unit for the sample for some positive integer n.
ex: suppose you want to inspect packages of potato chips coming off the Lays factory assembly line. A systematic sample would involve inspecting, for example, every 25th bag coming off the line.
probability sample
gives each member of the population a known chance to be selected
undercoverage
occurs when some groups in the population are left out of the process of choosing the sample
nonresponse
occurs when an individual chosen for the sample cannot be contacted or refuses to cooperate
response bias
occurs when an individual in a sample chooses an answer to a survey that he/she thinks is best rather than the answer that he/she truly believes
wording of question
may influence a person by leading the individual being questioned to one answer as opposed to another
experimental units
individuals on which the experiment is being done
subjects
experimental units that are people
treatment
the specific experimental condition applied to the units. The level of treatment is measured by the explanatory variable and the level of the variable we’re interested in is measured by the response variable.
factors
the explanatory variables in an experiment (i.e. the changes that are being imposed on the subjects in the experiment). Experiments may have several factors.
3 Principles of Experimental Design
CONTROL the effect of lurking variables on the response variable
RANDOMIZATION ensures that individuals are assigned to treatment groups by chance
REPLICATION of the experiments many times or on many subjects ensures that the results are not just due to chance variation
randomized comparative experiment
an experiment that has random assignment and a control or comparison group
statistically significant
an observed effect too large to attribute plausibly to chance
placebo effect
occurs when a subject receiving a placebo reacts favourably to it
block
a group of experimental units or subjects that are known before the experiment to be similar in some way that is expected to affect the response to the treatments. In a block design, the random assignment of units to treatments is carried out separately within each block. THE ASSIGNMENT OF SUBJECTS TO BLOCKS IS NOT RANDOM.
homogeneous group
another name for a block
matched pairs design
a special type of block design in which ONE of the two conditions is satisfied:
1) subjects are matched with themselves and given two different treatments (in a random order). This is the more commonly used form of matched pairs design.
2) similar subjects are matched and each assigned a different treatment.
blind experiment
the subjects involved in the study do not know which treatment that are receiving
double-blind experiment
neither the researches nor the subjects know who is receiving which treatment.
(the experimenters are aware)
researcher
the person measuring the response variable
experimenters
the people running the overall experiment, and are aware of who is receiving which treatment
lack of realism
serious potential weakness of experiments
