Schizophrenia is a psychological disorder which is sometimes referred to as split minds. Sufferers can be known to show symptoms of delusions, hallucinations as well as catatonic behaviour. If we are looking at the validity of something it means we are measuring what we are claiming to measure, and if we are looking at the reliability of something it means if we repeat the process over and over we should always get the same if not very similar results.
Schizophrenia is classified and diagnosed using two manuals, the DSM (diagnostic statistical manual) and the ICD (international classification of disorders). The DSM is used by America whilst the ICD is used in Europe. Instantly we see a lack in validity and reliability. Due to there being no universal definition of Schizophrenia, we are still inconsistent when diagnosing it or defining it. We are diagnosing psychological illnesses differently in different parts of the world so it is not consistent.
So although the diagnosis of Schizophrenia in Europe may be reliable in Europe, it is not reliable for use in America as they would be measuring Schizophrenia in a different way so it would lack validity and would lack reliability as they also see very different results due to the fact that the DSM states that symptoms should be there at least sixth months for diagnosis but the ICD states that symptoms have to be there for a month before diagnosis, so the numbers of people with Schizophrenia in America would most likely rise due to the fact that some people may only have a few episodes of Schizophrenia in their lifetime but due to the fact that these episodes may not last six months, they may never be diagnosed.
Also, it is unclear how Schizophrenia occurs. There are studies to prove genetics definitely play a part in Schizophrenia so we look at it using the biological approach, however, there are studies that prove that 1% of the population have Schizophrenia through no genetic or behavioural link. There is an explanation for each approach however, each of the studies seems to be reductionist by only looking at one approach and perhaps to understand Schizophrenia, a study should take place with an aim to involve all approaches. So it is still not understood enough for it to be reliable or valid as it is very rare to find two cases of Schizophrenia the same.