Scientific processes

Aim: a precise statement explaining the purpose of a study

Hypotheses: precise testable prediction of what is expected to happen

alternative hypothesis - predicts that differences in the DV occur as a result of the manipulation of the IV. Two types:

• directional (one-tailed)  - predicts the direction of the results
• non-directional (two-tailed) - predicts there will be a difference but does not predict the direction of the result

Directional hypotheses are used when previous research suggests that results will go in one direction, or when replicating a previous study that also used a directional hypothesis

null hypothesis - predicts that the IV will not affect the DV. Any results will be due to chance, not manipulation of the IV

Sampling: the selection of a participant to represent a wider population. Ideally, a sample is representative and results are aimed at a targeted population.

Random sampling: each member of the population has an equal chance of being selected

+ves:

• unbiased selection - no bias = representative sample
• generalisation - should be representative so can be generalised to target population

-ves:

• impractical - random sampling is difficult to achieve, not all members may wish to take part
• not representative - unbiased selection does not guarantee an unbiased sample

Opportunity sampling: involves selecting participants who are available and willing to take part, eg people passing on the street

Advantages:

• ease of formation - relatively easy to create
• natural experiments - opportunity sampling is usually used with natural experiments as the researcher has no control over who is studied

Disadvantages:

• unrepresentative - the sample is likely to be biased by excluding certain types of participants and thus be unrepresentative, so the findings cannot be generalised to the target population
• self-selection - pps have the option to decline = self-selected

Volunteer (self-selected) sampling: involves people who volunteer to participate.

Advantages:

• ease of formation - creating the sample requires little effort
• less chance of 'screw you' phenomenon - pps choose = eager to take part, so won't try to deliberately sabotage the study

Disadvantages:

• unrepresentative - the sample will be biased as volunteers tend to be a certain 'type' of person, thus making the results not generalisable to the target population
• demand characteristics - volunteers are eager to please which increases the chances of demand characteristics

Systematic sampling: taking every nth person from a list to create a sample. Involves calculating the size of the population and then accessing what size the sample needs to be to work out what the sampling interval needs to be

Advantages:

• unbiased selection - unbiased = representative sample
• generalisation - results are representative of the population

Disadvantages:

• periodic traits - the process of selection can interact with a hidden periodic trait within the population, so could be neither random nor representative of the target population
• not representative - unbiased selection does not guarantee an unbiased sample

A stratified sample is a small scale reproduction of a population and involves dividing a population into characteristics important for the research, eg by age/social class. Then the population is randomly sampled within each category

Advantages:

• representative - seeing as selection occurs from sub-groups
• unbiased - seeing as random sampling is performed upon sub-groups

Disadvantages:

• knowledge of population characteristics is required - may not be available
• time-consuming - the dividing of a population into stratums and then randomly selecting from each can take time

Pilot studies: small scale practice investigations carried out prior to research to identify potential problems