Data collection Flashcards
population definition
complete set of individual items you are interested in
census definition
measure value from every member of a population
sample definition
selection of observations taken from a subset of the population used to try find out information about whole population
adv of census
completely accurate view of population
disadv of census
time consuming
expensive
not possible if population constantly changes
not to be used if testing process destroys items
adv of sample
less time consuming + cheaper than census
fewer people have to respond
disadv of sample
data may not be representative of population
sample may not be large enough to give info about small minority of population
what causes different conclusions in different samples
natural variation
how to increase validity of conclusions from sample
increase sample size
requires more resources
sampling unit definition
individual item of population
sampling element definition
individual item of unit
parameter definition
number describing entire population
statistic definition
number taken from a single sample
sampling frame definition
list of sampling units of population individually named
random sampling features
every member of population has equal change of being selected
removes bias from sample
should be representative of population
includes simple random, systematic, stratified sampling
simple random sampling features
every member of population has equal change of being selected
chosen at random (lottery sampling, random number generator)
needs sampling frame
adv of simple random
considered fair
probably representative of population
each sampling unit has same change of being chosen
disadv of simple random
not possible without sampling frame
could be time-consuming, disruptive, expensive if population large
minority groups may be missed
systematic sampling features
choose starting point
select objects a certain number apart
only random of sampling frame has no order
adv of systematic
quick and easy to use
suitable for large samples/populations
disadv of systematic
not possible without sampling frame
may be missing values in population
sampling technique may coincide with periodic trait, no longer representative (bias)
stratified sampling features
population split into distinctly different groups (strata/stratum) that cover entire population
sample chosen in each group proportionate to frequency of group in population
adv of stratified sampling
minimises sample selection bias (no segment of population over/under represented)
sample reflects population
frequencies of each sample can be proportional to frequencies of each group in population
disadv of stratified
requires sampling frame
strata must be carefully defined
sometimes difficult to split into naturally occurring groups
biased sample definition
sample doesn’t represent population
non-random sampling methods
opportunistic sampling
quota sampling
opportunity sampling features
taking sample from target population available at the time
adv of opportunistic
easy to select sample
inexpensive
don’t need sampling frame
disadv of opportunistic
unlikely to produce sample representative of population
highly dependent on individual researcher (may not talk to mean member of target population)
quota sampling features
population split into groups (strata/stratum)
size of group in sample reflects their frequency in population
judgement used to selected members from each group until quota is filled (introduced bias)
adv of quota
sample should be representative of population
don’t need sampling frame
quick, easy, inexpensive
different groups’ responses can be compared
disadv of quota
non-random (could be biased)
have to be split into groups (may be difficult, time consuming)
non-responses (target population member not part of sample as quota filled) not recorded (may distort interpretation)
continuous variable definition
can take any value in a given range
quantitative variable definition
data associated with numerical observations
qualitative variable definition
data associated with non-numerical observations
have to count
discrete variable definition
can only take specific values in a given range
have to measure
knots in miles per hour
1 kn = 1.15 mph
