Dement & Kleitman (sleep and dream)
Evaluation Essay

P – Point (Strength/Weakness)E – Explain the pointE – Example from the studyR – Relate to the point on why is it a strength / weakness in the study
High in reliabilityThe extent to which a procedure, task, or measure is consistent. This is because the study had a standardised procedure for participants to follow.Participants were woken with a doorbell played by the researcher in a separate room and recorded their dreams with a tape-recorder that was placed next to their bed.The standardised procedure of apparatus used for all participants eases the process of replication of future research hence the study has high reliability.
Low on ecological validityThis refers to the extent that the setting a study has been conducted in can be relevant to everyday life.Participants slept in room inside a laboratory with electrodes attached to their eyes and scalp from the electroencephalogram (EEG) machine. Participants were woken multiple times throughout the night via a doorbell and had to recount the dream experienced into a tape recorder.The sleeping with different attachments on the head and inconsistent waking interval are not representative of real life as we experience a state of sleep for a long period with no interruptions, thus, the EEG readings and dreams experienced by the participants may not accurately reflect real life behaviours. Therefore, this study is low in ecological validity.
High in validityThe extent a researcher is testing what they claim to be testing. This is because the study was high in controls which ensured that there were no extraneous variables affecting the results of the study.

For example, the use of scientific equipment electroencephalogram (EEG) machine to identify the changes in brain wave pattern with the attachment of electrodes on the scalp.


This shows that the participants brain wave patterns are accurately identified by the EEG by detecting the changes in electrical activity in the brain. Hence this study is high in validity as researchers can confidently identify the sleep stages of either REM or NREM from reading of the EEG machine.
Low on generalisability

How widely findings apply to other settings and populations.

This is because, an unequal number of participants participated in this study which may lead to gender bias.

There were nine participants with seven males and two female adults.


The small sample size of nine is not representative of the population. There may be individual differences between males and females in dream pattern and the likelihood of recall lowering the generalizability of this study.
Self-report (weakness)

Participants own accounts of their behaviour or experience. Self-reports methods include questionnaires, interviews, thinking aloud, and diaries.

(Subjective report – vulnerable to participants mood, exhaustion level, etc.)

Participants were woken up with a bell, rung by the experimenter. Participants are then to speak to a tape-recorder if a dream is recalled.

Participant’s description of their dreams were subject to their expressive ability. There may be limitation in verbal command as a consequence from being asleep prior to expressing the dream experienced. Participants may report ‘no dream’ to get back to sleep making self-report a weakness.

Quantitative data (strength)

Describing human behaviour and experience using numbers and statistical analysis.

Data that focus on numbers and frequencies rather than on meaning or experience.

(Quantitative – objective, free from experimenter bias, easily comparable.)

Participant’s indication of dream recall or no recall when woken in either the REM or NREM stage were accumulated.

This allowed researcher to gather numerical data that were objective and requires little interpretation that is influenced by researcher’s personal opinions, thoughts and feelings. Therefore, quantitative data collected allowed researcher to analyse and compare dream recall results of participants woken in the REM stage (152) and in the NREM stage (11).

Other analysis:

Reductionism: the findings are all based around biological mechanisms affecting our dreaming state. Some psychologists may see this as being reductionist as there are psychological mechanisms that could be affecting dream content.

Observation: strength observations based on scientific equipment (EEG/EOG) so highly objective/reliable. They were observed by experimenters in a separate room, so they had some semblance of privacy to help them to sleep normally weakness observations in lab context (e.g. lab bed, wires) so may be unrepresentative of a normal night’s sleep weakness participants were aware that they were being observed and this alone may have affected their sleep, as we normally sleep without being watched.

Dement & Kleitman controlled many variables, such as pre-study levels of caffeine and alcohol, the doorbell sound, the EEG monitoring, etc. This means that another researcher could easily replicate this study to test it for reliability.

Participants had to sleep in an unusual environment (a laboratory) with electrodes attached to their head (EEG monitor) which is. of course, an artificial setting for them. Therefore, the study has low ecological validity.

Many laboratory experiments make participants take part in tasks that are nothing like real-life ones so they lack mundane realism. The task of being woken up and then asking to recall dream content or estimate dream length is not a normal activity for people to engage in. Therefore, the study lacks mundane realism.

The high levels of control so that participants all experienced the same conditions, such as the EEG monitoring and how data were recorded, mean that for each part of the experiment the researchers could confidently conclude cause and effect (e.g. that dream recall is affected by stage of sleep).

Generalisation: only five people were studied “in detail” and four more were used to confirm these findings. This could make it difficult to generalise beyond the sample of people because of the sample size.