Lesson 1 - 4

Sources of Errors in Sampling

Objectives• Understand how error can be introduced during

sampling

Vocabulary• Nonsampling errors – errors that result from the

survey process. Can be due to nonresponse of individuals selected, inaccurate responses, poorly worded questions, etc

• Bias – nonsampling error introduced by giving preference to selecting some individuals over others, by giving preference to some answers by wording the questions a particular way, etc

• Sampling errors – error that results from using sampling to estimate information regarding a population. Occurs because a sample gives incomplete information about the population

Sources of Nonsampling Error• Incomplete Frame• Nonresponse• Data Collection errors

– Interviewer error– Misrepresented answers– Data-entry (input) errors

• Questionnaire Design– Poorly worded questions– Inflammatory words– Question order– Response order

Sampling Error Non sampling Error

Iceberg Sampling Process

AnalysisProcess

Interviewer errors

Collection Execution

Data-entry (input) errors

DesignerIncomplete FrameQuestionnaire Design

Poorly worded questions Inflammatory words Question order Response order Subject

NonresponseMisrepresented answers

sample gives incomplete information about the population

Errors in Sampling

Four basic sampling techniques• Simple random sampling (SRS)

• Stratified sampling– Some of all

• Cluster sampling– All of some

• Systematic sampling

Summary and Homework

• Summary– Stratified and cluster sampling are

different– Convenience sampling results are

generally suspect

• Homework– pg 37-39: 11-22 (all), 24, 25