STAT 3615 Lecture Notes - Lecture 13: Survey Methodology, Missing Data, Questionnaire Construction
Lecture 5.1 Notes
Populations and Samples
• Population – consists of all subjects or items of interest. It is the group being studied
o Parameter – A numerical measurement describing a population
o Census – the collection of data from every member of a population
• Sample – a group selected from the population (a subset of the population). It provides
information used to infer information about populations
o Statistics – a numerical measurement describing a sample
Sampling
• Survey methodology studies the sampling of individual units from a population associated
sampling design techniques (questionnaire construction)
• Idea: to produce data in a way that is designed to answer our questions
• Key Idea: a REPRESENTATIVE sample
Choosing a Sample to Represent a Population
• Goals:
o Individuals in sample are representative of the population (that is, provide accurate
information about the population)
o Minimize cost of obtaining the sample (money, time, personnel, etc.)
Bias
• A survey method is biased if it has a tendency to produce an untrue value
• A couple types we will talk about:
o Measurement Bias
▪ Results from asking questions that do not produce a true answer
▪ Occurs when measurements tend to record values larger (or smaller) than the
true value
▪ Example: asking people, “How much do you earn?” It is likely that people will
report a value higher than their actual salary, resulting in an estimate that tends
to be too large.
▪ Sources of Measurement Bias
• Results from asking questions that do not produce a true answer
• Measurement bias can occur in a variety of situations including:
o Self-reporting of personal data
o The use of confusing, leading, or non-neutral wording in survey
questions
o Missing data, precise numbers, percentages, scales used
o Sampling Bias
▪ Occurs when a sample is used that is not representative of the population
▪ Some causes could be:
Document Summary
Populations and samples: population consists of all subjects or items of interest. It provides information used to infer information about populations: statistics a numerical measurement describing a sample. Sampling: survey methodology studies the sampling of individual units from a population associated sampling design techniques (questionnaire construction) Idea: to produce data in a way that is designed to answer our questions: key idea: a representative sample. Choosing a sample to represent a population: goals: Individuals in sample are representative of the population (that is, provide accurate information about the population: minimize cost of obtaining the sample (money, time, personnel, etc. ) Ex: internet polls: convenience sampling only sampling individuals that are convenient, small samples, non-responses. If a large percentage of those chosen to participate refused to do so or if people themselves chose to participate, the conclusions of the survey are suspect. Simple random sampling (srs: everyone in the population has the same chance of being chosen for the sample.
