Sampling and Data Collection

probability sampling

the probability of being chosen for each individual in the population is known

non-probability sampling

the probability of being chosen for each individual in the population is unknown

simple random sampling

every member in the population has an equal chance of being chosen for the sample

stratified random sampling

the population is divided into subgroups (strata) and simple random sampling is used to choose individuals from each subgroup (stratum)

cluster sampling

identify and sample clusters of individuals in a population

probability sampling advantages and disadvantages

non-probability sampling

the probability of being chosen for each individual in the population is unknown

• Very common in psychological research

• May not be representative of the population at interest

  • Some are more representative than others

• In some studies, may not be a big concern

convenient/haphazard sampling

recruiting from wherever feasible

quota sampling

choose a sample that reflects the composition of subgroups in a population. Use haphazard sampling to achieve this sample

Data collection

instructions

• clear

• allow participants to ask questions

• whether to inform participants about the hypotheses of the study?

  • placebo effect

  • demanding characteristics

• whether to inform experimenters about the hypotheses of the study?

  • experimenter bias

single-blind experiment

the participants are unaware of which condition (experimental or control) they’re in

double-blind experiment

the participants and experimenters are unaware of which condition (experimental or control) each participant is in

measure (and manipulaion) of IVs and DVs

• Reliability and validity

• Multiple DVs

• Sensitivity of measures

  • Ceiling effect

  • Floor effect

• Strength of manipulation (ex: length, dosage)

• Manipulation check

debriefing

ethical for participants to know the aims and hypotheses about the study

• Learn about participants’ thoughts and feelings, which can be helpful for interpreting results

pilot studies

a trial run with a small number of participants

• Do participants understand your instruction?

• How long does it take?

• Is the age group appropriate?

• Do you have floor/ceiling effects?