Reliability vs. Validity: know the difference or risk failing a 16 marker

They sound similar – but mix them up and you’ll confuse both the examiner and yourself.

Let’s get clear:

• Reliability = consistency. If the same result is produced repeatedly under the same conditions, it’s reliable.
  Example: A personality test gives you the same result every time = good reliability.

• Validity = accuracy. Does it measure what it claims to measure?
  Example: A test claims to measure intelligence but actually measures memory? That’s low validity.

There are types of both:

• Internal reliability (e.g., split-half method)

• External reliability (e.g., test-retest)

And:

• Internal validity (control of variables, avoiding confounding variables)

• External validity (generalising beyond the study – ecological, temporal, population validity)

Take Loftus and Palmer (1974) – the study on eyewitness testimony. Their findings raised questions about internal validity (were participants recalling real memories, or were they influenced by the verb used?). On the other hand, it had high control – boosting internal reliability.

Key point: A test can be reliable but not valid. You can consistently get the wrong result! But for a test to be valid, it must be reliable first.

Learn this distinction and use it wisely; it can earn you precious AO3 marks.