biostat 4
Non-probability sampling defined as subjective selection by researcher
Not based on random selection
Probability sampling involves random selection for strong statistical inferences
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Non-probability sampling easier and cheaper but higher risk of sampling bias
Weaker inferences about population compared to probability samples
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Probability sampling allows strong statistical inferences
Non-probability sampling based on convenience, easy data collection
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Non-probability sampling vs. Probability sampling differences
Subjective judgment vs. random selection
Unequal chance vs. equal chance for selection
Sampling bias not considered vs. used to reduce bias
Accurate representation vs. accurate sample creation
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Non-probability sampling used for qualitative, pilot, or exploratory studies
When randomization is impossible or budget/time constraints exist
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Types of Non-probability sampling:
Purposive Sampling
Convenience Sampling
Quota Sampling
Snowball Sampling
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Purposive Sampling (Judgement sampling) based on researcher's expertise
Used in qualitative research for detailed knowledge
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Convenience Sampling selects samples conveniently available
Easy recruitment, not representing entire population
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Quota sampling ensures representation of specific characteristics
Subjects from different subgroups with specific traits
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Snowball Sampling involves subjects identifying others
Used primarily for exploratory purposes
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Advantages of Non-probability sampling:
Reflect descriptive comments, cost-effective, time-effective
Disadvantages of Non-probability sampling:
Unknown proportion, lower generalization