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VALIDITY AND RELIABILITY IN PSYCHOLOGICAL RESEARCH

ROMAN TRNOVSKY


Dement, W. & KLEITMAN, N. (1957) Journal of Experimental psychology, 53, 339 - 46

• STUDY PERIODS OF PROLONGED RAPID EYE MOVEMENTS (REM) DURING THE SLEEP • CONNECTION BETWEEN THESE PERIODS AND THE EXPERIENCE OF DREAMS • 7 MALES, 2 FEMALES, 61 NIGHTS • 5 SUBJECTS – INTENSIVE STUDY • 4 SUBJECTS - CONTROL GROUP • MEASURE EEG, RECORD DREAM EXPERIENCE


HYPOTHESIS • Significant association between REM sleep and dreaming. • Significant positive correlation between the estimate of the duration of dreams and the length of eye-movement • Significant association between the pattern of eye movement and the context of the dream RESULTS • All subjects show REM periods every nights • Dreams recall predominantly after REM period • No dreams recall after non-REM period


No recall Dream recall Dream recall

No recall

N-REM REM

0

50

100

150

200

STRENGHTS • Replication - the experimental method consists of standardised procedures and measures which allow it to be easily repeated. • Particularly valid – experiment seems to measure eye movement and length of REM period


WEAKNESSES • Lack of ecological validity • the situation in which the participants had to sleep was unusual and could have affected their sleep patterns. • Nature of the method of waking participants may have affected their ability to recall their dream.

• Sample size - the sample size was small and only included 2 females so we could argue that the results were biased towards the dream pattern of men rather than women • Large differences between individuals in the reports of dreaming during REM. • Not supported findings a relationship between eye movements and what the person is dreaming about. • The method was very tightly controlled. For example the researchers were able to control the location, sleeping time and the participants use of stimulants.


• This authors concluded by stating that an objective measurement of dreaming had been accomplished by recording rapid eye movement during sleep. • Furthermore Dement and Kleitman’s conclusions have been replicated many times by other psychologists. • We cannot generalise from the results of a single experiment therefore the more often an experiment is repeated, with the same results obtained, the more confident we can be about the results.


GIBSON, E.J. & WALK, R.D. (1960) The ‘visual cliff’, Scientific American, 202, 64 – 71

• What does a new born baby see when it first open its eyes? • The question is significant because it bears on the important nature nurture debate within the field of visual perception. • Finding an answer might allow us to understand which of our perceptual abilities are inborn, and which abilities we have to learn.


• DEVELOPMENTAL PERSPECTIVE • Study of 36 infants, aged 6 - 14 months • Non-human animals were tested (lambs, chicks, kittens, turtles) at the age at which they show locomotion • The baby is placed in the middle of the glass, and its mother tries to get it to crawl either over the shallow end or over the deep end. HYPOTHESIS • Human babies have the ability to perceive depth, however can be implicated after the started moving. • Some animals are born with the ability to perceive depth.


RESULTS • 27 babies moved onto shallow side at least once. • 9 babies stayed where they were, did not crawl. • Only 3 babies crawled over the deep. • The failure of 25 per cent of the babies to respond at all. • A number of babies appeared to become very distressed.


STRENGHTS

WEAKNESSES

• Reliable - other studies have found same results with same procedures. • Valid - experiment seems to measure depth perception. Realistic visual cliff, could eliminate other senses like touch so they were measuring visual perception. • Ecological validity - cliff mirrors other experiences of drops in the environment. • Shows our behaviour is determined (controlled) by our biology which controls our senses (vision in this case).

• Individual differences at work - a few babies still crawled onto the deep side. • Sample too small to be representative of all babies, also American, so culturally biased. • Experimenter bias - the mums could give their babies subtle signals to not cross over to the deep side e.g. body language and this may have affected some babies. • Ethics - babies were distressed at being called over to the deep side by their mums. Should they be put under this distress?


STRENGHTS

WEAKNESSES

• Evidence for nature side of debate - we are genetically pre-wired to respond to our environment in certain ways e.g. avoid drops! • High internal validity - the researchers did measure what they claimed. The infant’s movement was a good measure of their ability to perceive depth. Also, babies are less likely to respond to demand characteristics as they won’t understand what the researcher is trying to find out!

• Ethnocentric - a lot of research is American and these findings are then used to explain behaviour in all cultural groups, but this is not correct. • Babies know they are being watched so may react to this in some way, lowering validity of results. • Babies were quite mature as they could have learned depth perception through their environment by that age, so we can’t see if depth perception is inborn (i.e. innate). • We can not tell what is going on in a baby’s mind so this calls into question the validity of the findings.


• Basic affordances are recognized by babies after born. • The survival of a species requires that its members develop discrimination of depth by the time they are able to move independently, be it at 1 day (the chick & goat) or 6-14 months (human). • That such a vital ability does not depend on possibly fatal accidents of learning in the lives of individuals is consistent with evolutionary theory. • Naturists belief - human born with certain capacities, however may not be functioning well until we mature physically. • Nurturists belief – human get these abilities through experience • Researchers could see if cliff avoidance behaviours were evident from birth in animal species.


• VALIDITY  Good specification of experiment could eliminate differences. (apparatus of walking cliff)  The researchers need to measure what they claimed. (babies movement onto sides of “cliff”; period of REM)

• RELIABILITY The experimental method consists of standardised procedures and measures which allow it to be easily repeated.

• SAMPLE SIZE Group size has to be large enough for good reliable results.


Evaluating Psychological Research - Presentation