Experimental Design Unit 1 Research Methods can be

Experimental Design Unit 1 Research Methods (can be examined in Unit 1&2)

I wonder if eating sugar will improve my memory?

So… you’ve managed to recruit 114 volunteers for your study… what now?

We have 3 options for experimental design: Independent groups: We split the 24 participants into two groups, 1 group has sugar, 1 doesn’t. They both do the same test and we compare results Repeated measures: All 24 people do the memory test with sugar. All 24 people then do the test without sugar. We then compare results. Matched pairs: We analyse the 24 participants before the study and put them into pairs based on how similar they are. E. g. we pair up Jo and Neve because they are the same age, fitness, weight, height, IQ etc. We give Jo sugar and Neve no sugar and compare.

Allocation of participants to conditions Random Allocation: The researcher should not have any influence over which participants go into which condition of a study. This would be a form of bias. In Independent Group design the researcher can use random allocation to achieve this; he might write 10 ‘A’ card and 10 ‘B’ cards and have the 20 participants randomly pick them out of a bag. In Matched Pair design each person in the pair must be randomly allocated a group; there could be 1 ‘A’ card and 1 ‘B’ card and each pair would have to pick the cards at random from a bag. Counterbalancing: With Repeated Measures design, all participants do each condition, but this could result in order effects. To even this out, Counterbalancing is used where half the participants start with one condition, and the other half start with the other condition

Strengths Independent Groups Repeated Measures Matched Pairs Weaknesses

Strengths Weaknesses Independent Groups • No order effects (getting better or worse at a task due to practice or tiredness) • Participants can’t work out the aim of the study because they only take part in one condition • There are differences about the participants in each half (participant variables) which is why the results might be different. • You need more people – to get 10 sets of results you need 20 people Repeated Measures • The participants in both conditions are • Order effects the same, so reduced number of • You might need to have two different tasks participant variables • People could work out the aim of the study as • You get twice as many results as they do both conditions other two methods! Matched Pairs • There are no order effects • Matching is difficult to do, it takes time and doesn’t always work • Some participant variables are still present.

I wonder if eating sugar will improve my memory? Let’s test it out!

Standardised Procedures Right. You now have to complete this memory test as fast as you can. Bring it outside to me when you’re done. Participant A Given sugar We need the same instructions and no extraneous variables! Hello! Can you have a go at completing this memory test for me. Take your time and relax. I’ll just wait here while you do it. Participant B Given no sugar

AQA Definition: Standardised procedures: A same method and set of instructions are used for all participants in the same condition when carrying out a study.

Instructions to Participants: Written or spoken information provided to participants before and during an experiment. If different things are said to participants then this could influence how they behave or perform during the study – another extraneous variable. Instructions need to be the same at 3 stages: 1) During briefing – what is said before the experiment to get a person to participate. Ethical information, consent, anonymity, right to withdraw etc. 2) Instructions about how to carry out the experiment 3) During debriefing – after the experiment when the aim of the study is given and the right to withdraw is emphasised.

Randomisation • Randomisation means using chance (e. g. tossing a coin) to decide order in an investigation • This should reduce bias • E. g. if you had a list of 2 words to learn and memorise, randomise the order of the words in the list.