Descriptive Statistics Flashcards
what is a variable?
something that varies
what does operationalising variables consist of?
explaining how a specific variable will be measured to represent a certain concept
problems with defining variables
- subjectivity and objectivity
- testability
what are measurements?
a way to describe real life factors by numbers
types of measurement scales
nominal
ordinal
interval
ratio
nominal scale
category data with no relationship between the number and measured label
ordinal scale
data placed in a relative ranking order, where the distances between scores vary
interval scale
at equal intervals and measurements along the scale
measures ‘magnitude’ and contains negative values (however zero is not meaningful)
ratio scale
interval scale and zero notes absolute absence, e.g., reaction time
what are measures of central tendency?
used to represent a group of scores
types of measures of central tendency
mean, median, and mode
mean
(sum of scores/number of scores)
this can be affected by outliers
median
midpoint of data
less affected by outliers, and is the best choice for ordinal data
mode
most occurring score
used if data is on a nominal scale and distribution can be bimodal or atypical
what are measures of spread?
how much the scores vary
types of measures of spread
range, interquartile range, and standard deviation
range
tells nothing about the scores between the minimum and maximum
interquartile range
measures the spread of the middle 50% of scores, between Q1 and Q3
standard deviation
the measure of data variation around the mean, that gives an indication of what happens between the minimum and maximum of a data set
the higher the SD, the _________________
larger the spread of scores
calculating the standard deviation
- calculate the mean
- work out how far each score is from the mean
- square these deviation scores
- add up these values
- divide by the number of scores
- square root
bar graphs
can contain ordinal and nominal data
can be vertical/horizontal, stacked, or histograms
histograms
a starting point for data distribution that can be useful for dealing with outliers
what do histograms show?
the number of participants with each specific score
stem-and-leaf plots
data is in a compact form and shows the size of data subsets
box plots
good for summarising and comparing multiple data sets
what are box plots able to summarise?
- lower quartile and upper quartile
- median
- minimum
- maximum
- outliers
what does Q3-Q1 provide?
the interquartile range
how can data be classed as an outlier?
if it is 1.5x the IQR
scatterplots
show the relationship between variables
