What is the fundamental difference between reliability and validity?

Reliability refers to the consistency and stability of a measure (getting the same result repeatedly), while validity refers to the accuracy of a measure (measuring what you actually intend to measure). A measure can be reliable without being valid, but it cannot be valid without being reliable.

How does 'dependability' in qualitative research compare to 'reliability' in quantitative research?

Dependability is the qualitative equivalent of reliability; while quantitative reliability seeks replicability of results through statistics, dependability seeks to show that the research process was consistent and that findings are supported by a clear audit trail.

What is the difference between inter-rater reliability and test-retest reliability?

Inter-rater reliability measures the level of agreement between different observers looking at the same data, whereas test-retest reliability measures the stability of a single instrument over time by administering it to the same subjects twice.

Why is it a mistake to assume that a high reliability coefficient (like Cronbach's Alpha) means a test is 'good'?

A high reliability coefficient only means the items are consistent with each other; it does not mean the test is actually measuring the correct construct (validity) or that the items are free from systematic bias.

What is the 'Researcher as Instrument' error in qualitative reliability?

It is the misconception that qualitative research is unreliable because it is subjective. In reality, qualitative reliability is maintained by acknowledging the researcher's role and providing transparent documentation of how their perspective influenced the data analysis.

Can a study be valid if it is not reliable?

No. If a measurement is inconsistent and fluctuates randomly (unreliable), it cannot accurately capture the true value of what is being measured (invalid). Reliability is the foundation upon which validity is built.

What is Cronbach's Alpha ($\alpha$)?

It is a statistical measure of internal consistency used in quantitative research to determine how closely related a set of items are as a group. It ranges from 0 to 1, with values above 0.7 generally considered acceptable for reliability.

What is an 'Audit Trail' in research?

An audit trail is a transparent description of the research steps taken from the start of a project to the development and reporting of findings. It includes raw data, notes on transitions, and the rationale for coding decisions to ensure dependability.

Define 'Internal Consistency'.

Internal consistency is a measure of reliability that assesses how well different items on a test that are intended to measure the same construct produce similar results. It ensures that all parts of the instrument are contributing equally to the measurement.

What is 'Inter-coder Agreement'?

This is a qualitative technique where two or more researchers independently code the same data using a shared set of criteria. High agreement suggests that the coding process is consistent and not just a result of one person's unique interpretation.

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Reliability of Qualitative & Quantitative Methods

Summary

Reliability is a fundamental criterion for evaluating the quality of research, representing the consistency, stability, and repeatability of results. While quantitative research emphasizes statistical precision and replicability through standardized instruments, qualitative research focuses on 'dependability' and the transparency of the research process to ensure that findings are consistent with the data collected.

1. Definition & Core Concepts

Reliability refers to the degree to which a research instrument or procedure produces consistent results across repeated applications. It is essentially a measure of 'repeatability'—if the study were conducted again under identical conditions, it should yield the same findings.
In Quantitative Research, reliability is often viewed as the absence of random error. It assumes an objective reality that can be measured precisely using standardized tools like surveys or physiological sensors.
In Qualitative Research, reliability is frequently reframed as Dependability. Because qualitative research acknowledges the changing nature of human experience and the researcher's role as an instrument, reliability focuses on whether the research process is logical, traceable, and clearly documented.

Diagram illustrating the difference between reliability and validity using a target analogy. The left target shows a tight cluster of points away from the center (reliable but not valid), while the right target shows a tight cluster in the center (both reliable and valid).

2. Quantitative Reliability Principles

Internal Consistency: This measures how well different items on a single test or survey measure the same construct. It is typically quantified using Cronbach’s Alpha ( $\alpha$ ), where a value closer to $1.0$ indicates higher reliability.
Stability (Test-Retest): This involves administering the same test to the same group of people at two different points in time. A high correlation between the two sets of scores suggests that the instrument is stable over time.
Equivalence (Inter-rater Reliability): This assesses the degree of agreement between different observers or coders. If multiple researchers use the same criteria to evaluate a phenomenon and reach the same conclusion, the measurement is considered reliable.

3. Qualitative Reliability (Dependability) Principles

4. Key Distinctions

5. Exam Strategy & Tips