Controls
- Experimental controls are used in scientific experiments to prevent factors other than those being studied from affecting the outcome
- They are needed to eliminate alternate explanations of experimental results
- There are several ways to control experiments
Randomisation
- Randomisation refers to the deliberate avoidance of bias on the part of the researcher in order to keep the research as objective as possible:
- Participants are randomly assigned to one condition of the IV e.g. by selecting names at random out of a hat
- Random allocation to condition ensures that no bias has intruded over which participants take part in which condition
- If the procedure involves a list of words, digits or images presented to participants then the list must be decided randomly to avoid researcher bias
- Due to the nature of randomness one condition of the IV may result in a group of all female participants or a word list may have words beginning with the same letter appearing one after the other at the start of the list
Counterbalancing
- Counterbalancing is relevant to repeated measures designs and is implemented as follows:
- The researcher splits the participants in half e.g. 20 in one group, 20 in the other group
- One group completes the conditions in this order: condition A followed by condition B
- The other group completes the conditions in this order: condition B followed by condition A
- Counterbalancing is used to control for order effects (practice, fatigue, boredom)
Standardisation
- Standardisation is the term used to describe the identical procedure set up in an experiment (or the questions used in self-report measures) across all conditions/participants which involves:
- Instructions given to the participants
- Briefing prior to the procedure (including the consent form) and debriefing after the procedure has taken place
- Number of participants per condition e.g. in an experiment with a sample size of 40, the researcher would ensure that there were 20 participants per condition
- Timings: each condition of the IV should run for the same amount of time e.g. 15 minutes for condition A; 15 minutes for condition B (unless one of the conditions includes a time-delay)
- Materials: identical materials must be used, the only exception being if the materials need to change for the IV to be implemented e.g. condition A involves learning a poem underwater and condition B involves learning a different poem on land (a repeated measures design)
-
- Implementing standardisation allows the research to be replicated and reliable
