making observations with unmanipulated variables; making correlations
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experimental study
making observations with a manipulated variable; investigating cause and effects
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controlled experiment
changes one variable at a time
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independent / explanatory variable
variable being manipulated
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dependent variable / response variable
produces data necessary to support or refute hypothesis
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constants
aspects of the experiment kept the same
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confounding variable
a variable that links the independent and dependent variable and could be affecting the outcomes
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experimental units
objects being experimented on; humans referred to as subjects
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four principles of experimental design
comparison, random assignment, controls / constants, replication
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comparison
the experiment compares two or more treatments
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random assignment
using chance to assign treatments to groups
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controls / constants
variables kept the same in an experiment
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replication
using enough experimental units in an experiment
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placebo effect
any outcomes from the dummy treatment
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double-blind experiment
researcher and subject are unaware of which treatment is which
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population
entire group we want information about
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census
collects data from every individual in the population
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sample
subset of individuals from population which we actually collect data from
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convenience sample
choosing easy to reach individuals from the population
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voluntary response surveys
people decide whether to join the sample; creates bias since strong-opinioned people will only want to participate
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simple random sampling
every group of n individuals in population has an equal chance to be selected (hat method)
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stratified random sampling
classify population into homogenous groups (strata) and take SRS of them
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cluster sampling
classify groups into heterogenous groups (geographically) and take SRS of all the clusters; cluster chosen must be used
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systemic sampling
randomly choose starting point in population and select every kth member
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undercoverage
occurs when some members of the population could not be chosen
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nonresponse
when participant of experiment cannot be reached or refuses to participate
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response bias
the person asking questions could potentially affect data (systemic incorrect responses)
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wording of question
manner of question asked could potentially affect answer
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qualitative data
shown in bar graphs, frequency / relative frequency tables, pie chart
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quantative data
shown in histograms, stem plots, dot plots, box and whisker plots
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two-way table
two categorical variables organized according to a row and column variable
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marginal distribution
using the "margins" of the data
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mean
average of the data (use x with bar from sample mean and fancy u for population mean)
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median
midpoint of distribution when data is arranged smallest to largest
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interquartile range (IQR)
middle half of the data (Q3 - Q1)
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five number summary
minimum, Q1, median, Q3, maximum
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two ways to measure spread
IQR using quartiles and median; standard deviation using mean
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standard deviation
measures average distance of observations from mean; calculated by finding average of the squared distances and taking square root (s for sample and fancy o for population)
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skewed right
when data values are concentrated on left and less values are on the right; mean is greater than median (dinosaur tail points right)
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skewed left
when data values are concentrated in right and less values on the left; mean is less than median (dinosaur tail points left)
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symmetric
when data values are centered; mean and median is the same
Studied by 44 people
