experimental design + types of experiments

repeated measures (design)

each participant completes each of the experimental conditions

strengths of repeated measures

removes participant variables so increases internal validity

fewer participants needed

limitations of repeated measure

demand characteristics and may guess the aim of the study this decreases internal validity

order effects

independent groups(design)

different participants in each condition

strengths of independent groups

helps to remove demand characteristics as are less likely to guess the aim so increase as internal validity

order effects are eliminated increase the validity of the findings

limitations of independent groups

participant variable may affect the validity of findings as diff people diff characteristics

more participants needed so longer and more expensive

matched pairs(design)

participants paired up based on similar characteristics eg iq scores or baseline memory test

strengths of matched pairs

participants variables are controlled increasing reliability

demand characteristics are reduced as each ppt only tested once

limitations of matched pairs

time consuming process

can never be fully accurate so lack of consistency lowers the reliability

lab experiment

takes place in a controlled or artificial settings

level of control is very high reasearcher control variables tightly

strengths of a lab experiment

easier to establish a cause-effect relationship because of high levels of control

high internal validity

use of standardised procedure means that the research is replicable which increases reliability

limitations of lab experiments

use of artificial tasks means it lacks ecological validity

findings are difficult to generalise beyond the sterile lab setting

because ppt knows in experiment demand characteristics may limit generalisability if findings

lowere external validity

field experiment

conducted in a natural everyday setting lower level of control some variables are harder to manage

strengths of field experiments

as the research is conducted in real settings artificiality is reduced

less likely to experience demand characteristics so high validity

limitations of field experiments

extraneous variables are more likely to happend meaning reliability is reduced

harder to replicate so reducing ability to check for consistency

natural experiment

IV changes naturally and researcher doesn’t manipulate low level of the

researcher observes, measures and records the natural changes and responses which have occurred due to the naturally occurring phenomena

strengths of natural experiments

allows research into topics that would otherwise be unethical to study eg mental illness or natural disaster -high ethical validity

high in ecological validity-researcher doesn’t control

limitations of natural experiments

casual relationships are difficult to determine due to variables at play -reduced reliability

could be bias

quasi experiment

IV based on pre existing characteristics(age gender) reasearcher can control some aspects

strengths of quasi experiments

due to lack of manipulation on iv results have higher external validity

limitations of quasi experiments

ppt cannot be randomly allocated this can lead to ppt variables making it unreliable

lack internal validity as there may be other factors that could explain the results

pilot study

a small scale trial of pressures materials and instructions before the main study, to ensure clarity improves reliability and helps identify problems