Class Notes on Experimental Design and Sampling Techniques

Class Structure and Homework Assignments

  • Students are given class time to complete homework.
  • Homework is due in one week if not finished in class.
  • Chapter one homework is likely due on Friday of next week.
  • Students are encouraged to stay up to date with homework to prevent last-minute stress.

Attendance and Student Engagement

  • Instructor checks attendance by calling out names of students present in class.
  • Students are reminded about a bonus point system for attendance.
  • Emphasis on participation and being engaged.

Winter Weather Considerations

  • Mention of an approaching snowstorm (referred to as "snowmageddon").
  • No Zoom lectures will be conducted as they are deemed awkward and ineffective.
  • Discussion about adapting to weather changes without relying on digital lectures.

Overview of Experimentation

Main Concepts in Experiments

  • What Makes a Good Experiment: Randomization is a key factor.
  • Definition of Randomness: Everything or every subject must have an equal chance of selection for treatment groups.

Example of Randomization

  • Example discussed about testing two medicines: one real and one placebo.
  • Random assignment is needed to ensure that results are valid.

Potential Issues with Randomization

  • Risk of unbalanced groups, especially regarding characteristics such as age.
  • Older individuals may require longer recovery from illness, leading to potential bias if all are placed in one treatment group.

Solution: Randomized Block Design

  • Utilize a technique called randomized block design to ensure balanced representation across treatment groups.
    • Each group must contain a representative sample, preventing age-related bias.
    • Example scenario: Ensuring equal numbers of older subjects in both treatment groups.

Importance of Replication

  • Replication is crucial for validating experimental results.
    • Results must be replicable by others using the same methods.
    • Example provided concerning the Innocence Project involving DNA testing: all DNA samples must leave enough material to allow for retesting.

Statistical Concepts

  • Transition from discussing populations to samples within statistics.
  • Introduction of common sampling methods that help researchers obtain valid data.
    • Four primary sampling methods will be detailed below.

Common Sampling Methods

1. Simple Random Sample (SRS)

  • Definition: A simple random sample is drawn from the entire population with every individual having an equal chance of selection.
  • Example method for random selection could involve drawing names from a hat.

Electronic Random Selection

  • Example use of Excel function =RANDBETWEEN(lower limit, upper limit) to randomly select individuals or items from a defined population.
  • Importance of using unique identifiers (e.g., student ID numbers) for accurate random selection.

Advantages of SRS

  • Reduces bias significantly by ensuring diversity within the sample.

Bias Consideration in Simple Random Sampling

  • Acknowledgment of the chance that a sample could still be biased despite randomness due to variable grouping (i.e., all individuals from one side of the classroom).

2. Stratified Random Sample

  • Definition: In stratified sampling, the population is divided into subgroups (strata) and a random sample is taken from each stratum.
  • Example of strata could include characteristics like major, living situation, or year of study.

Advantages of Stratification

  • Reduces bias more effectively than simple random sampling as it ensures all groups are represented.

Limitations of Stratified Sampling

  • More time-consuming and complex to implement compared to simple random sampling.

3. Cluster Sample

  • Definition: Instead of randomly selecting individuals from the entire population, whole clusters (groups) are selected at random.
  • Example: Selecting entire classrooms or dorms to represent a larger population.

Risks of Cluster Sampling

  • Potentially introduces bias if selected groups do not represent the overall population.
  • Example discussed involving a study focusing on one fraternity to assess campus party culture.

4. Systematic Sample

  • Definition: Using a systematic method to select individuals, often by choosing every n-th member from a list.
  • Example: If selecting every third person from a list of class members during a survey.

Application of Systematic Sampling

  • Practical for situations like cafeteria reviews where multiple groups of people are surveyed systematically instead of randomly.

Convenience Sampling

  • Definition: A method where the sample is taken from a group that is easy to access or sample.
  • Potential Issues with Bias: Convenience sampling is likely to introduce bias as it does not represent the larger population well and often lacks randomization.
  • Example provided regarding media coverage of public opinions at diners, which might not reflect broader public sentiments.

Critical Factors Impacting Statistical Studies

1. Law of Small Numbers

  • Refers to drawing conclusions about a population based on a small sample size.
  • Example: A study sampling one classroom out of thousands and generalizing the results to the entire student population.

2. Confounding Variables

  • Issues arise from not accounting for external factors that might influence the results of a study, such as socioeconomic status influencing intelligence, which should be taken into account in research.

3. Data Manipulation

  • Ethical concerns raised regarding intentional or unintentional data manipulation leading to false conclusions in research.

Important Ethical Considerations in Research

  • Ensure that participants are informed of all relevant risks when partaking in studies.
  • Analysis of historical research indicating failure to disclose risks and implications (e.g., various unethical experiments conducted in the past).

Wrap-Up and Future Tasks

  • Students will work in small groups for chapter one investigations to analyze data and implement sampling techniques learned.
  • Emphasis on collaboration in groups of two to five students for completing future assignments effectively.

Homework and Projects

  • Encouragement to start homework assignments promptly to avoid last-minute issues.
  • Clear expectations set for group work and future investigations in class on Friday.