experimental method, designs, types, and sampling

what is the aim of experimental methods

what researcher intends to investigate

what is the experimental method hypotheses

a statement of what research believes is true

2 types of hypotheses

directional- changes are greater or less, positive or negative

non-direction- only states a difference, correlation, association

what does the researcher manipulate and record

iv and records effect of iv on dv

TRUE OR FALSE there are different levels of the IV

true

extraneous variables

any variable other than iv that may affect dv if not controlled

demand characteristics

any cue from researcher or research situation that may reveal the study aim

investigator effects

any effect of researcher/investigator behaviour on research outcome, dv

what is random allocation

ppts allocated to conditions in independent groups design using random method to control participant variables

counterbalancing

control order effects in repeated measures design. half ppts do tasks in one order, other half in opposite order

randomisation

use of chance (tossing coin) when designing investigations to control bias effects

standardisation

using same formalised procedures for all ppts in research study, otherwise differences could act as ev

what are control groups and conditions

independent groups- control group used for comparison, acts as baseline and helps establish causation

repeated measures- controlled condition set as baseline

single blind trial vs double blind trial

single- ppts dont know study aims, demand c reduced

double- ppts and researcher dont know study aims, demand c and researcher bias reduced

independent groups

group 1 does CA and group 2 does CB, ppts randomly allocated to experimental groups

name 2 strengths of independent groups

1. no order effects, ppts only tested once, cant be bored or benefit from practice effect, controls important ev

2. will not guess aim, ppts tested once, higher realism

2 limitations of independent groups

1. ppts variables, ppts in 2 groups are different, ev, may reduce validity of study

2. less economical, need 2x many ppt as repeated m for same data, more time spent recruiting = expensive

repeated measures

all ppts take part in all conditions, order of conditions should be counterbalanced to avoid order effects

give 2 strengths for repeated measures

1. ppts variables, same characteristics in both conditions, controls important ev

2. fewer ppts, ½ number of ppts than ig, less time spent recruiting

give 2 limitations of repeated measures

1. order effects, ppts may do better or worse when doing similar task twice, practice/ fatigue effects, reduces validity of results

2. ppts guess aims, change behaviour, reduce validity of results

matched pairs

2 groups of ppts, related to each other, paired on important ppts variables for experiment

what are the 2 strengths for matched pairs

1. ppts variables, ppts matched on relevant variable, controls ppts variables and enhances results validity

2. no order effects, ppts tested once, no practice/fatigue effects, enhances results validity

what are the 2 limitations for matched pairs

1. matching isnt perfect, time consuming, cnt control all relevant variables, cant address all ppts variables

2. more ppts, need 2x many ppts as rm for same data, more time recruiting=expensive

lab experiment

controlled enviro, ev regulated, generally ppts go to researcher, iv manipulated and effect on dv recorded

state 2 strengths for lab experiment

1. ev controlled, effect of ev on dv minimised, cause and effect between iv and dv demonstrated, high internal validity

2. more easily replicated, greater control=less chance ev introduced, findings can be confirmed, supports their validity

state 2 limitations of lab experiment

1. lack generalisability, control lab envrio unlike real life, ppts aware theyre being studied, unnatural behaviour, lower external validity

2. demand c, cues in experimental situation invites particular response from ppts, lower interal validity

field experiment

natural, everyday setting, researcher goes to ppts, iv deliberately changed and effect on dv recorded

2 strengths for field experiment

1. natural enviro, ppts more comfortable, authentic behaviour, results ore generalisable, high external validity

2. ppts unaware theyre being studied, more likely to behave naturally, high external validity, generalisable results

2 limitations of field experiment

1. difficult to control ev, observed changes in dv not due to iv but ev, difficult to establish cause and effect than in lab

2. ethical issues, no informed consent, invasion of ppts privacy

natural experiment

experimenter doesnt change iv but it does change by someone or something else, dv ma be natural occurring or devised by experimenter and measured in field or lab

what are 2 strengths of a natural experiment

1. only practical/ ethical option, manipulate iv may be unethical, natural ex may be only way causal research can be done

2. greater external validity, natural ex involve real world issues, findings more relevant to real experiences

what are the 2 limitations of a natural experiment

1. event may occur rarely, reduces opportunity for research, may limit scope for generalising findings to other situation

2. ppts not random allocated, experimenter has no control which ppts placed in which condition, iv is pre-existing, result in uncontrolled ev

quasi experiment

iv based on pre-existing difference between people, no one can deliberatly change this variable, dv may occur naturally or devised by experimenter and measured in field or lab

give 2 strengths of quasi experiment

1. often high control, carried out in controlled conditions, replication is possible

2. comparisons can be made, iv not controlled by researcher, comparisons between different types of people can be made

give 2 limitations of quasi experiment

1. no random allocation, experimenter has no control over this, ppts may cause dv to change, acting as ev

2. causal relationships not demonstrated, researcher doesnt manipulate or control iv, cant say for certain if dv change was due to iv

what is a population

large group of people that a researcher is interested in studying

what is a sample

smaller group of target population

what is generalisation

sample is draw should represent the population so generalisations can be made

what is bias

bias in certain groups that may be over or under represented

random sample

every person in target pop. has equal selection chance, using lottery method

what is lottery method

all members of target pop. given a number and a computer or phone randomiser used or names are drawn from hat

one strength of random sample

potentially biased, ev are controlled, enhances internal validity

2 limitations of random sample

1. time consuming, complete list of pop. is hard to get, selection is from biased list

2. selected ppts may refuse to take part, lead to unrepresented sample, turns into volunteer sample

systematic sampling

organised list of target pop. e.g postcodes, every nth person is selected from list

one strength of systematic sample

unbiased,, first item is usually selected at random, objective method

one limitation of systematic sample

time and effort, complete list is needed, random sample may be better to use

stratified sample

sample reflect proportions of people in certain subgroups in a pop.

example of how a stratified sample works

gender or age, relative % of subgroups in pop. are reflected in sample

state a strength of a stratified sample

representative method, characteristics of target pop. represented, generalisability more likely than other methods

state a limitation of a stratified sample

not perfect, cant reflect all different subgroups of pop. complete representation isnt possible

opportunity sample

people who are most available, ask people nearby

give a strength of a opportunity sample

quick method, convenient, more economical and most popular

give a limitation of opportunity sample

inevitably biased, unrepresentative of target pop. draw from a specific area, findings cant be generalised

volunteer sample

ppts select themselves, e.g from newspaper ad

what is one strength of a volunteer sample

ppts comet o you, more engagement than being stopped in the street, more economical

what is one limitation of a volunteer sample

volunteer bias, ppts may share certain trait, respond to cues and generalisation limited