Sampling Flashcards
Population and sample
- Population ~ Large group of ppl that researcher interested in
- Sample ~ Smaller group
- Generalisaton ~ Representative of population so generalisations can be made
- Bias ~ over or under represented
Random sample
. Equal chance
. Lottery method. All members of target population placed in randomiser
+ Potentially biased -> EVs & CVs controlled -> enhances internal validity
- Time consuming + may not work -> complete list of population is hard to get -> Some may refuse to take part
Systematic sample
. Using set system ~ selected using set pattern (sampling frame)
. Every nth person selected from list of target population
+ Unbiased -> 1st item usually selected at random -> Objective method
- Time + effort -> Complete list of population required -> May as well use random sampling
Stratified sampling
. Strata ~ Sample reflects proportions of people in certain subgroups (strata) within population
. Subgroups (strata) identified. Relative percentages of subgroups in population are reflected in stratified sample
+ Representative method -> Characteristics of target population represented -> Generalisability more likely than other methods
- Stratification is not perfect -> Strata cannot reflect all ways in which people are different -> Complete representation is not possible
Opportunity sample
. Most available ~ nearest/easiest to obtain
. Ask people nearby
+ Quick -> Convenient, use people closest -> Cheaper, 1 of most popular sampling methods
- Inevitably biased -> Sample unrepresentative of target population as it is drawn from v specific area eg 1 street in 1 town -> Findings cannot be generalised
Volunteer sample
. Self selecting
. Advertise
+ Parts willing -> Know how much effort and time is needed -> Likely to engage more than people stopped in street
- Volunteer bias ~ Participants may share certain traits eg want to be helpful -> Respond to cues and generalisation limited
