descriptive statistics Flashcards
what is a variable?
something that changes
what does operationalised variable mean?
specific statement about how a variable will be measured
what are the problems with defining variables?
- subjectivity vs objectivity
- testability
what are the 4 types of measurement
- nominal scales
- ordinal scales
- interval scales
- ratio scales
how do scales differ in relationship (2)
- the properties of the numbers
- the properties of what is being measured
what is a nominal scale?
numbers merely label
no relationship between number size and attribute measured
what is ordinal scale?
order of size of numbers = order of size of attribute measures
ordered
distance between scores vary
what is interval scales?
eqaul intervals on scale = equal intervals in property measured
measure magnitude
zero = no meaning
what is ratio scales?
interval scale AND zero means something
example of ratio scale
the time taken for ppt to press button
example of interval scale ?
degrees celsuis
example of ordinal scales?
IQ score
example of nominal scales?
numbers on buses
what are the measures of central tendency
mean
median
mode
what is the mean?
average
add all then divide by how many there is
what is the median?
midpoint of the sample after data has been put in order
when to use the mean?
if all values are important and valid
when to use the median?
if there are outliers
best choice for ordinal data
what is the mode?
score that occurs the most
when to use the mode?
nominal scale
can be bimodal (two)
what are the limitations of using the mode?
- some data sets have no mode
- some data sets have more than one mode
- the mode can be atypical
when can you use the mode (4)
nominal
ordinal
interval
ratio
when can you use the median (3)
ordinal
interval
ratio
when can you use the mean? (2)
interval
ratio
what are 3 ways to measures of spread of data?
- range
- interquartile range
- standard deviation
what is the range?
difference between highest and lowest number
what is 1 problem with the range?
tells us nothing about the scores between the min and max scores
what is the interquartile range?
measures the spread of the middle 50% of scores
between 1st and 3rd quarters
what is standard deviation?
measure of variation around the mean
higher the SD = larger spread of scores.
what does the standard deviation do?
gives an indication of what is happening between min and max of data set
how to calculate the standard deviation?
- calculate the mean
- work out how far each score is from the mean
- square deviation scores
- sum this
- sum of scores / number of scores
- square root the variance
what is it called when we mimic the mean in standard deviation
the variance
what is a graph?
visual methods of representing data
what do graphs do?
indicate patterns within the data
why do we use graphs?
- decide how to analyse our data
- illustrate findings
what are the 4 types of graphs?
- bar graphs
- stem and leaf plots
- box plots
- scatterplots
what is a histogram?
type of bar graph
what are stem and leaf plots?
data in a compact form
show size of data subsets
can have two digits
what do box plots summarise? (5)
- lower and upper quartile
- median
- minimum
- maximum
- outliers
what are scatterplots?
show the relationship between variables
what are box plots good for?
comparing more than one data sets
why are histograms and stem and leaf plots used? (3)
- show frequency of values
- show overall pattern
- spot outliers
why are bar plots used?
data on nominal scale
what must be done before running a statistical analysis?
data must be plotted
