AL

algebra 2 notes #3

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.