• Population: group of individuals a researcher seeks to learn about from a research study
  • Sample: the group of individuals chosen from the population to represent it in a research study
  • Sampling error: the difference between the observations in a population and in the sample that represents the population in a study
  • Probability sample: chosen with a specific probability o Probability of population is known
  • Convenience/Purposive Sample: that the probability of an individual being chosen cannot be determined
  • Simple random: each member of the population has an equal probability of being selected o Students are chosen randomly from list of all student at a university o Reduces sampling error

o Difficult to ensure that each member of a large population can be chosen in a sample

  • Cluster: a subset of clusters is randomly chosen to sample from o Identifying all hospitals in different areas of the US and then randomly choosing 10 hospitals to sample from
  • Makes it easier to choose members from smaller clusters
  • Can ignore segments of the population that are not in the clusters chosen for the sample
  • Stratified random: proportion of the group in a sample is equal to that of the population o Registered voters are randomly selected from a list of Democrats and Republicans to equal the proportion of registered Democrats and Republicans in the US
  • Reduces bias
  • Can be difficult to ensure equal probability of being chosen from a large population
  • Convenience/Purposive samples: probability of choosing an individual in the population is NOT known
  • Haphazard/volunteer: based on convenience and on who volunteers o Sample is chosen from students who volunteer to complete and extra credit assignment o Easier to obtain

o May not represent the population properly due to selection bias

  • Quota: the proportion of a group in the sample is equal to that in the population
  • Volunteers are recruited from students in a psychology course such that the gender breakdown in the sample is the same as the gender breakdown of all students at the school
  • Allows for better representation of a characteristic
  • May not represent the population properly due to selection bias because random sampling is not used

 

Chapter Summary:

  • In probability samples, the probability of an individual being chosen from the population is known, and participants are chosen randomly from the population.
  • Convenience samples , the probability of an individual being chosen is not known, and the participants are chosen in a non random matter
  • Probability samples are typically more representative of the population and have less sampling error
  • Convenience samples is used when a population is too large to allow all individuals to be identified for sampling
  • The internet is a useful tool for recruiting a representative sample that may be larger than a sample that is recruited in person
  1. Questions:
    1. In a _________ sample, individuals are chosen at random from the population, but are chosen in proportions equivalent to proportions that exist in the population 

Ans: Stratified random

    1. In a _________ sample, individuals who volunteer from the population are chose for the sample

Ans: Haphazard

  1. The difference in observations between the population and the sample 

Ans: Sampling error

  1. The ____________ is the group of individuals a researcher wants to learn about, whereas a ______________ is the group of individuals who serve as subjects in a study 

Ans: Population; sample

  1. In a _________ sample, all members of the population have an equal chance of being selected

Ans: Simple random sample

  1. A biased sample will lower the ___________ of the study

Ans: Validity