RM experiments

• Systematic sampling


  Not representative
• sample size wanted/100 x percentage size of sub group = stratified sampling (if they give %)
• Explain why opportunity sampling might not be the most representative of the target population

  PPTs picked from the sample are present in the same place at the same time, doing similar things therefore might have similar personalities - making it difficult to generalise findings to the wider population
• stratified the most representative?

  It accurately reflects the make-up of the target population in the correct proportions, meaning the findings can be generalised
• Opportunity sampling is less time consuming as less money is required because you choose who is available at the time for your sample, unlike random sampling which takes a long time to identify everyone in the target population
• Volunteer sampling is quick, easy and cheap to carry out as all you do is place an advert for the study where the target population will be unlike random sampling which takes time to place names in a hat and give the population an equal chance of being picked
• volunteer sampling might not be representative bc

  Only certain personality types will volunteer (extrovert/curious) making it difficult to generalise the findings to the target population
• systematic sampling not be representative =

  Not everyone has an equal chance of being picked therefore it is difficult to generalise the findings to the target population
• systematic sampling avoid researcher bias =

  The researcher has no influence over who is chosen to take part in the study - as it is objective once the system to select ppts is established
• more appropriate to generalise the findings for stratified sampling =

  Stratified sampling accurately reflects the make-up of the target population in the correct proportions
• CONTROLS HELP TO INCREASE INTERNAL VALIDITY.
• Problem with independent groups design - Individual differences are a possible issue Because there are different ppts in each condition, therefore in one condition the ppts may have a particular trait that makes them perform better at the DV (CONTEXT) – meaning it wasn’t the IV that affect the DV, lowering the internal validity.
• Control individual difference - Random allocation. ensures each Ppt has same chance of being in one condition as any other condition, therefore it is unlikely that all ppts in one condition will share a characteristic to help them perform better at the DV. HOW:

  1. Write the names of the ppts on equal sized pieces of paper.

  2. Put the paper in a hat

  3. Then randomly pick out ppts names an place half in condition 1 and the other half in condition 2 (CONTEXT).
• Problem with repeated measures design- Order effects are a possible issue when a repeated measures design has been used. Ppts take part in all conditions and so may perform better in the second condition (due to practice) or worse in the second condition (due to fatigue), or the 1st condition may have lasting effects on the 2nd conition. (CONTEXT)
• Control order effects= Counterbalancing (ABBA) method. To control and reduce order effects HOW:

  1. Half the Ppts complete condition A then condition B. (CONTEXT)

  2. The other half complete condition B first then condition A.

  3. Order effects are balanced/distributed across both conditions. Top tip: Never say order effects have been eliminated…they haven’t!!
• The group of people who are the focus of the researcher’s interest are called the population (or target population).
• A sample is a group of people taken from the target population to take part in the research. It is assumed that the sample is representative of the target population.
• 1. Random sampling

  2. Systematic sampling

  3. Stratified sampling

  4. Opportunity sample

  5. Volunteer sample
• Random Sample Every person in the target population has an equal chance of being selected. Create a complete list of all the target population. Write names on equal size pieces of paper and put in a hat. Without looking select the number you want in your sample from the hat.
• random allocation ao3- Potentially unbiased as everyone in the target population has an equal chance of being selected for the study (CONTEXT). This means any extraneous variables will be equally divided between the different groups. This increases the internal validity.
• random allocation -Very time consuming because it takes time and can be difficult collecting all the names of participants to take part in the study (CONTEXT) and it is not guaranteed participants would want to take part in the research.
• Systematic Sample A ‘system’ is applied to select Ppts. Create a sampling frame to organise the target population e.g. put all the people in the target population in alphabetical order. Decide on the system e.g. very 5th or 10th person is chosen until there are enough ppts for the sample.
• systematic sample ao3- Avoids researcher bias as the researcher has no influence over who is chosen to take part in the study (CONTEXT) as it is objective once the system to select ppt is established.
• systematic sampling- sample may not be representative as not everyone has an equal chance of being picked therefore it is difficult to generalise to the target population (CONTEXT). Moreover, creating the system and collecting names could be time consuming and difficult for the researcher.
• Stratified Sample= advanced way of sampling where make-up of the sample reflects the proportions of certain sub-groups in the target population.

  1. Identify the different sub-groups that make up a population e.g. males/females.

  2. Calculate how many of each proportion you would need for your sample size e.g. if you wanted a sample of 80 ppts what would 70% of 80 be.

  3. No. of Ppts which make up each proportion are chosen using random sampling.
• ao3 stratified sampling -Very time consuming because it takes time working out the proportions of Ppts needed (CONTEXT) and it is not guaranteed participants would consent to take part.
• ao3 stratified sampling- Most representative sample as is it accurately reflects the make-up of the target population (CONTEXT) in the correct propotions/amounts meaning findings can be generalised to the target population. Stretch: however,
• Opportunity Sample Being there at that moment in time –eg waiting for participants in the canteen during period 3 and asking the first 30 ppts who walk past to participate.

  How? Go somewhere we you will have access to the population you want to study and ask the first 30 ppts who are there at that moment in time if they will take part.
• ao3 opportunity sample- Very quick, easy and less money is required as as you choose who is available at the time for your sample (CONTEXT) unlike random sampling which takes a long time to identify everyone in the target population and make a list of all names.
• ao3 opportunity sample- May not be representative of the target population, those picked by an opportunity sample are present in the same place at the same time, doing similar things, (CONTEXT) therefore they may have similar personalities (E.G), making it difficult to generalise findings to the wider population.
• Volunteer Sample- This is ‘self selected’ method where people volunteer themselves to be participants, E.g. placing an advert for participants then waiting for the first 30 replies. How? Place an advert where people in the target population will see it and wait for the first 30 people to reply.
• ao3 volunteer sample - Very quick, easy and cheap to conduct as all that is required is to place an advert for the study in a place the target population may be (CONTEXT) and wait for ppt to volunteer to take part in the study (number) unlike random sampling which takes time to place names into a hat and give the population an equal chance of being picked.
• Hypothesis This is a specific, testable statement in which the researcher predicts what will happen between the variables.
• Directional: There will be significantly higher/faster/more (operationalised DV) when participants (one condition of IV) compared to when participants (other condition of the IV)
• Non-Directional: There will be a significant difference in (operationalised DV) when participants (one condition of IV) compared to when participants (other condition of the IV)
• ‘There will be NO significant difference = NULL
• Extraneous variables. Unwanted extra variables other than the IV (1 mark) that could have an effect of the DV, this would lower the internal validity of the study
• There are 3 main causes of extraneous variables

  • Situational factors - things to do with the environment the research is carried out in e.g. task difficulty OR standardised instructions.
  • Participant variables - things to do with the Ppts e.g. ages, gender, IQ, eye sight, hearing, personality. TOPT TIP!! These can only be used for an independent groups design, not matched pairs or repeated measures.
  • Experimenter variables - things to do with researcher e.g. investigator effects.
• when an extraneous variable is not controlled for and it DOES affect the DV and so it becomes a confounding variable.
• LAB EXP =experiment conducted in lab which is highly controlled environment, (1 mark) where the researcher manipulates (changes) the independent variable (IV) and measures the effect on the dependent variable (DV)