P1.R.1Formulation of testable hypotheses, including null and alternative hypotheses; identifying independent and dependent variables

A psychological investigation begins with a clear, testable hypothesis. There are two main types:

• Null hypothesis (H₀): there is no difference / no relationship between conditions. ("There will be no difference in recall between participants who study music and those who study in silence.")
• Alternative hypothesis (H₁): there is a difference / a relationship. The alternative can be directional ("music will reduce recall") or non-directional ("music will affect recall in either direction"). Use directional when prior research justifies it; non-directional when not.

Operationalisation

Both variables must be operationalised — defined precisely enough to be measured. Vague: "music affects revision". Operationalised: "playing instrumental music at 60 dB during a 10-minute revision period reduces the number of correctly recalled facts on a 20-item test."

Independent variable (IV)

The variable the experimenter manipulates. In the example above, IV = presence/absence of music (or three levels: silence / instrumental / lyrics).

Dependent variable (DV)

The variable the experimenter measures. Here, DV = number of correct items recalled.

Co-variables

In correlational research there is no IV/DV; the two variables are co-variables because neither is manipulated. Hypothesis form: "There will be a positive correlation between hours of revision per week and exam performance."