A research team wants to estimate the current prevalence of clinical depression among all adults in one district. Its final sample consists of 3,000 adults who volunteered after invitations were sent through GP practices. Each volunteer completes an anonymous questionnaire scored using the current ICD-11 criteria and allows the researchers to check their GP record. Both methods cover the same two-week period.
| Method | Population used as the denominator | Percentage meeting the measure |
|---|---|---|
| Anonymous questionnaire | The same 3,000 volunteers | 6% |
| Current diagnosis in GP records | The same 3,000 volunteers | 3% |
Use the data and information about the methods to explain what the difference between the two percentages suggests and why neither percentage should be treated as the exact prevalence among all adults in the district.
144 exam-style questions on OCR GCSE Psychology 3.2 Theories/Explanations, covering 3.2.1 Clinical characteristics of schizophrenia, 3.2.2 Key statistics of schizophrenia, 3.2.3 Dopamine hypothesis of schizophrenia, 3.2.4 Brain structure and function in schizophrenia; criticisms, 3.2.5 Social drift theory of schizophrenia, 3.2.6 Schizophrenia research study: Daniel et al. (1991), 3.2.7 Clinical characteristics of clinical depression, 3.2.8 Key statistics of clinical depression, 3.2.9 Social rank theory of clinical depression, 3.2.10 ABC Model of clinical depression, and 3.2.11 Clinical Depression research study: Tandoc et al. (2015). Each one has a worked solution and a mark scheme showing where the marks go.