Sampling Methods

Sampling Methods

1. RANDOM SAMPLE

   • Process
     • Every person in the target population has an equal chance of being selected. The researcher obtains a list of all the members in the target population then uses a computerised random generator or "names out of a hat" method to select a required number of participants
   • Strengths
     • Free from researcher bias- the researcher has no control over who gets selected
   • Weaknesses
     • Time consuming
     • A representative sample is not guaranteed- there is a chance some sub-groups may be over-represented or missed out

2. SYSTEMATIC SAMPLE

   • Process
     • A sampling frame is produced, followed by a sampling system where every nth person is picked
   • Strengths
     • Free from researcher bias- the researcher has no control over who is picked
     • Fairly representative
   • Weaknesses
     • Not entirely unbiased unless the number selected for sampling is chosen randomly, i.e. start with this person and and choose every nth person thereon

3. STRATIFIED SAMPLE

   • Process
     • Involves dividing the the population into groups based on a quality called strata, random samples are then collected from each stratum
   • Strengths
     • Avoids researcher bias because the members selected from each stratum are randomly selected
     • The sample represents the strata composition
   • Weaknesses
     • It may lack a 100% representation because individual differences cannot be accounted for

4. OPPORTUNITY SAMPLE

   • Process
     • The researcher selects anyone who is willing to take part, and then asks the participants to ask anyone else they know who may be willing to take part to do so
   • Strengths
     • Convenient- saves time and effort
   • Weaknesses
     • Unrepresentative of the target population
     • Suffers from researcher bias as the researcher has complete control over who gets selected

5. VOLUNTEER SAMPLE

   • Process
     • The researcher puts an initial advertisement in a newspaper/magazine etc and participants self select themselves
   • Strengths
     • Requires minimal input from the researchers
   • Weaknesses
     • Volunteer bias- only atypical members of the target population respond (i.e. the most co-operative and responsive)
     • Only people who see the advert have a chance of being selected, reducing the generalisability of the findings