Statistics and probability

• Sampling Method


  Procedure for selecting sample elements for a population
• Population


  Includes all the elements from a set of data
• Sample


  Consists of one or more observations from the population
• Parameter


  Measurable characteristic of a population such as mean or standard deviation
• Statistic


  A specific characteristic of a sample
• Random Number


  A number determined totally by chance with no predictable relationship to any other number
• Non-probability Sampling


  • Does not rely on the use of randomization techniques to select members
  • Not all elements in the population frame have an equal chance of being selected
• Convenience or Accidental sampling


  • Sampling strategy based on the convenience of the researcher
  • Members or units are selected based on availability
• Purposive sampling


  • Members of a particular group are purposefully sought after
  • The researcher uses his good judgment in selecting the respondents who best meet the purpose of his study
• Snowball sampling


  • Identification of a few persons who met the requisite characteristics
  • These persons act as informants to identify others who qualify for inclusion in the sample
  • Process continues until the desired number of respondents is reached
• Quota sampling


  • Identify a set of important characteristics of a population
  • Select desired samples in a non-random way
  • Assumes the samples will match the population with regard to the chosen set of characteristics
• Probability Sampling


  • Uses randomization
  • Takes steps to ensure all members of a population have a chance of being selected
• Random Sampling


  • Method of selecting a sample from a universe such that each member of the population has an equal chance of being included in the sample
  • All possible combinations of size have an equal chance of being selected as sample
• Lottery Sampling


  • Assign numbers to the participants of your population
  • Write the numbers on small pieces of paper
  • Roll the papers and put them in a container
  • Shake the container thoroughly and pick the desired number of participants
• Table of Random Numbers


  • Uses columns or rows of numerical digits which were mechanically generated
  • Digits used should be equal to the digits of the population
  • Samples are selected by taking the digits in the column or row which are equal or less than the total number of population
  • Each population number is taken just once
• Stratified Sampling


  • Population divided into subgroups (strata)
  • Members are randomly selected from each group
• Systematic Sampling


  • Selecting the numbers of a sample that allows only chance and a "system" to determine membership
  • A system is a planned strategy for selecting members after a starting point is selected at random
• Cluster Sampling


  • Divides the population into clusters
  • Clusters are randomly selected
  • All members of the cluster are sampled