3.4.11—Experiment practical

A laboratory experiment manipulates an independent variable, measures a dependent variable and controls or randomises other influences. Random assignment helps balance participant differences so causal claims are more defensible.

Standardisation improves reliability, but artificial tasks, demand characteristics and narrow samples can reduce ecological or external validity. Ethics, debriefing and informed consent remain part of the design.

If participants are randomly assigned to two memory instructions and tested with the same list, a difference in scores supports an effect of the instruction under those conditions. It does not automatically generalise to real classrooms.

Control is not the same as realism and a significant result is not a universal law. State the manipulation, comparison, sample and validity boundary.

To conduct the practical: state a directional or non-directional hypothesis; operationalise the independent and dependent variables; decide whether random assignment makes it a true experiment or a pre-existing group makes it quasi-experimental; control or record plausible confounds; standardise instructions; obtain teacher permission, consent and debriefing; pilot the task; collect the required sample ethically; analyse the planned comparison; then report effect, uncertainty, demand characteristics and limits on causality and generalization.