91Ó°ÊÓ

A study is conducted to determine whether people learn better with routine or crammed studying. Subjects volunteer from an introductory psychology class. At the beginning of the semester 12 subjects volunteer and are assigned to the routine studying group. At the end of the semester 12 subjects volunteer and are assigned to the crammed studying group. a. Identify the target population and the sample. b. Is this an observational study or an experiment? c. This study involves two kinds of non-random sampling: 1. Subjects are not randomly sampled from a specified population and 2. Subjects are not randomly assigned to groups. Which problem is more serious? What effect on the results does each have?

Step by step solution

01

Define the Population and Sample

The target population includes all students in an introductory psychology class, as they represent the group of interest for the study. The sample comprises the 24 subjects who volunteered for the study, with 12 assigned to routine studying and 12 to crammed studying.

02

Determine Study Type

This is an observational study because the researchers are observing the effects of the two studying methods on the participants without any controlled intervention or manipulation, such as random assignment to groups.

03

Analyze Non-random Sampling Issues

The more serious problem is that subjects are not randomly assigned to groups. This impacts the internal validity of the study, as it can lead to biased results due to pre-existing differences between groups. Non-random sampling from the population affects external validity, but the lack of random group assignment can directly skew the study's findings and conclusions.

Unlock Step-by-Step Solutions & Ace Your Exams!

• Full Textbook Solutions

  Get detailed explanations and key concepts

• Unlimited Al creation

  Al flashcards, explanations, exams and more...

• Ads-free access

  To over 500 millions flashcards

• Money-back guarantee

  We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Observational Study

An observational study is a type of research where researchers observe and measure outcomes without manipulating any variables. In the given exercise, the study observes the effects of routine versus crammed studying on student learning. The key distinction of observational studies is that the subjects are observed in their natural setting without any interference from the researchers.

• Researchers do not introduce any treatments or changes to the subjects.
• The focus is on gathering data as naturally as possible.
• This approach can often identify correlations but not causations.

A limitation of observational studies is their inability to control for potential confounding variables, which can influence the results. However, they provide valuable insights, especially when experimental manipulation is not feasible or ethical.

Non-random Sampling

Non-random sampling occurs when participants are not selected randomly from the entire population, which can lead to biased results. In this exercise, students volunteered for the study, which is a form of non-random sampling.

• Non-random sampling can introduce selection bias, as participants may have certain characteristics that influence the study results.
• It limits the generalizability of the findings, affecting the external validity of the study.

The major concern with non-random sampling is that it can lead to skewed data that do not accurately represent the whole population, thus impacting the overall credibility of the study's findings.

Population and Sample

Understanding the concepts of population and sample is fundamental in any research. The population is the entire group of individuals or instances about whom the research is concerned. In this case, it’s all students in an introductory psychology class.

• A sample is a subset of the population that is actually observed in the study.
• Here, the sample is the 24 students who volunteered, 12 in each study group.

Random sampling from the population would help ensure a representative sample, which is crucial to increasing the study's external validity, as conclusions drawn would be more applicable to the entire population.

Internal Validity

Internal validity refers to the extent that a study can establish a cause-and-effect relationship between the independent and dependent variables. It focuses on the accuracy and trustworthiness of the study's findings.

• The lack of random assignment to study groups in this exercise is a threat to internal validity.
• Groups may differ in other ways besides the studying method, leading to confounding variables that affect the results.

Ensuring high internal validity often requires a controlled experimental design, where participants are randomly assigned to different groups. This mitigates potential biases and clarifies the relationship between variables.

External Validity

External validity is about the extent to which research findings can be generalized to and across other situations, people, settings, and times. One primary concern in the exercise is how well the results apply beyond the sample studied.

• Non-random sampling impacts external validity since volunteers might not represent the broader student population.
• Without external validity, it’s uncertain whether the results are applicable outside the scope of the sample.

Strengthening external validity requires ensuring that the sample is representative of the larger population, often achieved through random sampling and diverse selection of participants. This way, conclusions drawn can be confidently extended to other similar scenarios.