Reliability refers to the consistency and repeatability of test scores or research findings. It can be measured through tools like the Kuder-Richardson 20 for binary tests. Reliability can be internal, measuring how well a test assesses what it intends, or external, assessing if results generalize. Validity refers to what a test or procedure actually measures. Internal validity ensures instruments measure what they aim to, while external validity generalizes results beyond the study. Research instruments can be researcher-completed like rating scales or subject-completed like questionnaires. Descriptive case studies use quantitative and qualitative data to describe an observed population.

1. RELIABILITY AND VALIDITY
GROUP 4

2. RELIABILITY
• Reliability is a measure of the stability or consistency of test scores. You can also
think of it as the ability for a test or research findings to be repeatable. For example,
a medical thermometer is a reliable tool that would measure the correct
temperature each time it is used. In the same way, a reliable math test will
accurately measure mathematical knowledge for every student who takes it and
reliable research findings can be replicated over and over. tools you can use to
measure reliability.
• For example: Kuder-Richardson 20: a measure of internal reliability for a binary test
(i.e. one with right or wrong answers).

3. It can be:
• Internal vs. External Reliability
Internal reliability, or internal consistency, is a measure of how well your test is
actually measuring what you want it to measure. External reliability means that your
test or measure can be generalized beyond what you’re using it for. For example, a
claim that individual tutoring improves test scores should apply to more than one
subject (e.g. to English as well as math). A test for depression should be able to detect
depression in different age groups, for people in different socio-economic statuses, or
introverts.

4. VALIDITY
• Examples:
• Internal validity - the instruments or procedures used in the research measured
what they were supposed to measure. Example: As part of a stress experiment,
people are shown photos of war atrocities. After the study, they are asked how the
pictures made them feel, and they respond that the pictures were very upsetting. In
this study, the photos have good internal validity as stress producers.
• External validity - the results can be generalized beyond the immediate study. In
order to have external validity, the claim that spaced study (studying in several
sessions ahead of time) is better than cramming for exams should apply to more
than one subject (e.g., to math as well as history). It should also apply to people
beyond the sample in the study.

5. INSTRUMENT, VALIDITY, RELIABILITY
Researcher-completed Instruments Subject-completed Instruments
Rating scales Questionnaires
Interview schedules/guides Self-checklists
Tally sheets Attitude scales
Flowcharts
Performance checklists
Personality inventories
Achievement/aptitude tests
Time-and-motion logs Projective devices
Observation forms Sociometric devices

6. Explanation by earlier events. In natural sciences the explanations are traditionally sought in
the past: what were the reasons which caused the later state of things? This type of explanation
is called causal, for example: "The bridge collapsed because of strong wind and a fault in its
construction".
Contextual explanation. Sometimes the explanation is found by showing the function that the
activity fulfils in its context. E.g., a bird sings in order to mark out its territory and to keep
rivals away, thus securing the food that the offspring need. Products of human culture are often
explained by the concurrent state of society.
Explanation by later events. This is common when explaining the acts of people. E.g., "The
Eiffel tower was built to serve as landmark and symbol for the Paris exhibition."
Explanatory Case Study

7. DESCRIPTIVE CASE STUDY
• Descriptive research includes both quantitative and qualitative data and uses these
types of data to describe the population being observed. For example, someone
interested in why certain groups of trees are dying, while others of the same type
and in the same location are thriving, can observe the trees and their surrounding
environment to come to a preliminary decision. At its core, this is descriptive
research.