Reliability and validity

Introduction to Reliability and Validity

In Psychology, it isn’t enough to just carry out a study; we need to know if the results actually mean something! Imagine using a ruler to measure your height, but the ruler is made of stretchy elastic. One day it says you are 150cm, the next day it says 160cm. That ruler is not reliable. Now imagine using a ruler that is solid, but the numbers are printed in the wrong places. It might give you the same measurement every time, but it’s not your true height. That ruler is not valid.

In this chapter, we will explore how psychologists ensure their research is consistent (reliability) and truthful (validity). These are the two "golden rules" for any psychological investigation.

1. What is Reliability?

Reliability is all about consistency. If a piece of research is repeated and the results are the same or very similar, we say the research is reliable.

How do we achieve reliability?

To make sure a study is reliable, psychologists use standardised procedures. This means every participant is treated in exactly the same way. They get the same instructions, the same tasks, and are tested in the same environment. This makes the study replicable (others can copy it to check the results).

Key Takeaway: If you see the word "reliability," think "Consistency: would I get the same result twice?"

2. What is Validity?

Validity is about accuracy and truthfulness. It asks the question: "Is the study actually measuring what it claims to measure?"

There are different ways to look at validity:

Internal Validity: This is about whether the results were really caused by the variables the researcher was looking at, or if something else (like an extraneous variable) messed up the results.

Ecological Validity: This is a type of external validity. It refers to whether the results of a study can be applied to real-life situations. If a study is done in a very artificial lab, it might have low ecological validity because people don't act like that in the real world.

Key Takeaway: If you see the word "validity," think "Truth: is this a true reflection of behavior?"

3. Reliability and Validity in Research Planning

When psychologists plan their research, they have to consider how their choices affect these two factors. Let’s look at how they apply to the different methods you have studied in Topic 11.

A. Sampling Methods

Generalisability is closely linked to validity here.

• Validity: If a sample is stratified or random, it is more likely to represent the target population. This means the results are more "valid" for that whole group.
• Reliability: Using an opportunity sample is often less reliable because the researcher might just pick people who are available at that specific moment, making it hard to get the same sample again.

B. Experimental Designs

How you group your participants affects your results:

• Repeated Measures: This can lower validity because of order effects (participants get bored or practiced), so they aren't behaving naturally. However, it is good for reliability because you are comparing the same people to themselves!
• Independent Measures: This can lower validity because of participant variables (one group might just be naturally better at a task), meaning the results might not be a "true" reflection of the IV's effect.

C. Quantitative vs. Qualitative Methods

Quantitative methods (numbers, like closed-ended questions):

• High in reliability because they are easy to repeat and use objective data.
• Sometimes lower in validity because they don't give "why" answers, so they might miss the true meaning.

Qualitative methods (words/descriptions, like open-ended interviews):

• High in validity because they provide rich, detailed information about how a person really feels.
• Lower in reliability because everyone’s answers are unique, making it very hard to replicate the exact same data.

4. Objectivity and Subjectivity

To help improve reliability and validity, psychologists try to be as objective as possible.

Objectivity

Being objective means the researcher does not let their personal feelings or opinions influence the data. Scientific methods like laboratory experiments are usually objective because they use facts and measurements. Objectivity increases reliability.

Subjectivity

Being subjective means the results are based on a personal point of view or interpretation. For example, in an unstructured interview, the researcher might interpret a participant's answer based on their own opinion. Subjectivity can lower reliability but can sometimes help validity by providing deeper insight.

Quick Review: The "Target" Analogy

Don't worry if this seems tricky! Imagine a person shooting arrows at a target:

• If all the arrows hit the same spot but it's not the bullseye: That is Reliable but not Valid.
• If the arrows are scattered all over the place: That is Neither Reliable nor Valid.
• If all the arrows hit the bullseye: That is Both Reliable and Valid!

Common Mistakes to Avoid

1. Mixing up the definitions: Remember: Reliability = Repeatable/Consistent. Validity = Very accurate/True.

2. Forgetting Ecological Validity: Students often forget that "validity" isn't just about the test being correct; it's also about whether the test works in the real world.

3. Assuming Lab Experiments are always better: While Lab experiments have high reliability (because they are standardised), they often have lower ecological validity because they are artificial.

Summary Table

Note: For more information on how these concepts apply to specific research methods, see the chapter on "Research methods: experiments, interviews, questionnaires, correlation, case study, observation".