8. Adoption studies - Kety - 1968

How can adoption studies help us separate nature from nurture?

• Twins are put up for adoption, they are placed with different families.

• If they both develop schizophrenia it can be deduced that it is because of genetics/nature.

• If one develops it but the other doesn’t, it can be deduced that it is because of the environment they are in/nurture.

What type of experiments/studies are these and why?

• Natural studies because there is no way to control the IV.

• These studies have to be natural because it would be morally wrong to separate twins intentionally.

What was the aim of Kety’s study?

• To investigate if there is a genetic basis for schizophrenia.

What kind of experiment is this?

• A natural experiment.

• Because adoption and schizophrenia are naturally occurring variables.

What is the IV?

• Biological relatives and adoptive relatives of schizophrenia sufferers.

• Schizophrenia sufferers and a control group with no mental illness.

What is the DV?

• The researchers measured the prevalence of schizophrenia related mental illness among family members.

What is the design of the study?

• Independent groups design - as it looks at the difference between biological relatives and adoptive relatives of schizophrenia sufferers (index Pp)

• It also looks at the difference between the schizophrenia sufferers and a control group with no history of mental illness.

What was the sample method used?

• Opportunity sample

How many Pp made up the sample?

• 34 schizophrenic patients - two were MZ twins.

• Taken from the Danish Adoption Register for Copenhagen.

• They were taken from a larger sample of 503 adoptees who had been admitted to psychiatric hospitals with general mental illnesses.

What was their age range?

• 20-43

How many Pp were in the control group?

• 33 mentally healthy controls were selected from the Danish Adoption Registry.

• They were matched to the schizophrenic patients on age, gender, the age they were adopted and the social class of the adoptive family.

What were the 3 sub groups they were split into?

• B1 - group of 16 patients with chronic (long term) schizophrenia.

• B2 - group of 7 patients with acute (short term) schizophrenia.

• B3 - group of 11 patients with ‘borderline schizophrenia’

How were the assessments of schizophrenia made?

• Kety used the Danish family records to locate adoptive and biological relatives of the Pp.

• He tracked down 463 relatives and used the mental health register to access their mental status.

• A panel of 4 psychiatrists used the medical records to diagnose family members.

• This was a 'blind test' because the psychiatrists did not know whether the records were from an adoptive or a biological family member. - Blind testing reduces experimenter bias increasing internal reliability, internal validity, and inter-rater reliability.

• Once the diagnosis had been made the identities were revealed and they were assigned to adoptive family groups (IA and CA) or the biological family groups (IB or CB)

• The psychiatrists diagnosed the family members in categories of schizophrenic spectrum disorders.

• In 4 cases they couldn’t reach a conclusion and these relatives were dropped from the study.

Who was involved in this process?

• A panel of 4 Danish psychiatrists used the medical records to diagnose family members.

• This was a 'blind test' because the psychiatrists did not know whether the records were from an adoptive or a biological family member. -Blind testing reduces experimenter bias.

What do these results mean?

• They found more spectrum disorders in the index participants biological families than in the controls biological families.

• The research also found more signs of schizophrenic spectrum disorders in the index Pp biological families than their adoptive family.

What is the conclusion?

• There seems to be a genetic component to schizophrenia because schizophrenia adoptees were more likely to have schizophrenia in their biological family than in their adoptive family.

• And their biological families were more likely to have schizophrenia than the families of controls.

What are the evaluation points for Generalisability? - A03

• Danish population - white low levels of migration.

• Hard to generalise the results to other ethnic groups or to more mixed populations.

• Poor population validity/ethnocentric.

• Males and females used.

• Broad age range used.

What are the evaluation points for Reliability - A03

• Kety developed a reliable procedure and replicated 3 more times - adding interviews in it as well.

• Since they got similar results, this gives it good external reliability - as it can be tested and retested.

• psychiatrists did not know whether the records were from an adoptive or a biological family member.

• Blind testing reduces experimenter bias increasing the internal reliability of results.

• It increases the inter-rater reliability because other psychiatrists can check for the same results.

• Kety also used a panel of 4 psychiatrists who diagnosed each relative based on medical records

• Relatives were assigned to categories when they agreed.

• There were only 4 cases where the psychiatrists couldn’t agree - these were removed from the study.

• Good inter-rater reliability.

What are the evaluation points for Application? - A03

• If schizophrenia has a genetic component, then even an upbringing among a healthy adoptive family might not prevent a child with a genetic predisposition for schizophrenia becoming ill in later life.

• However, the diathesis-stress model suggests this is only a predisposition and it requires a trigger.

• If families are aware that a child has a genetic link to schizophrenia, they can guide a child away from drugs and stressful careers and watch out for early symptoms.

• As with most mental illnesses, schizophrenia is less destructive if it diagnosed earlier.

What are the evaluation points for Validity? - A03

• psychiatrists did not know whether the records were from an adoptive or a biological family member.

• Blind testing reduces experimenter bias - increasing the internal validity of results.

What are the evaluation points for Ethics? -A03

• The participants in this study were not directly approached: only their data was analysed by the researchers and this could be done under Danish laws without needing consent from the participants.