Sampling Methods

• Definition of Sampling Methods: Techniques for selecting individuals from a population to gather data for surveys.

Proposed Scenario

• Population: Students at LHS with Instagram accounts.

• Options: Studying everyone in Libertyville, students at LHS, or all LHS students. Only the last option is valid since it focuses on our target group.

Types of Sampling Methods

Convenience Sample

• Description: Involves members of the population that are readily available.

• Examples:

  • Asking students in the hallway during passing period.

  • Surveying classmates in the cafeteria or sports team members.

• Bias: High potential for bias as certain groups may be underrepresented. For example, surveying only one class excludes freshmen and seniors.

Self-Selected Sample

• Description: Participants volunteer to be part of the study.

• Examples:

  • Sending an email to the student body and collecting responses.

  • Posting a flyer or a QR code for students to participate voluntarily.

• Bias: There can be bias; those who feel strongly about a topic are more likely to volunteer, skewing results.

Systematic Sample

• Description: Organizes the population in a specific order, then selects participants at regular intervals.

• Examples: Taking every 10th or 30th student from an ordered list, such as alphabetical or by ID number.

• Bias: Low potential for bias, as this method tends to represent the population more equitably, provided the list is comprehensive.

Random Sample

• Description: Every member of the population has an equal chance of being selected.

• Examples:

  • Drawing names from a hat or using a random number generator to select students.

• Bias: Minimal potential for bias since selection is truly random.

Study Methods

Observational Study

• Description: Collecting data by observing subjects without interference.

Controlled Study

• Description: Divides the sample into two groups; one receives treatment, the other does not (control group). Common in pharmaceutical studies.

Survey Method

• Description: Asking questions directly to participants to gather data.

Example Analysis

• Observational Study at Mall:

  • Standing in the mall and recording what people buy is an observational study.

  • Bias: Yes, because it ignores those who shop online or do not shop at the mall which may not represent the overall community.

• Pharmaceutical Study:

  • Volunteers tested for a new drug with a control group (placebo) demonstrates a controlled study.

  • Sampling method is self-selected as it involves volunteers.

• Systematic Sampling at School:

  • Asking every 12th student entering school for study habits represents systematic sampling.

  • Potential bias stem from the time frame (07:45 to 08:15), possibly excluding late arrivals.

• Survey on School Timing:

  • Neutral question phrasing (e.g. appropriate timings) has less bias compared to leading questions that may skew opinions.