Quantitative research is research based on the collection of data in numerical quantities. It is concerned with hypothesis testing, reliability and validity. It can be classified broadly as observational, which includes case control, cross-sectional and cohort studies, and experimental, which includes the classic controlled trial. 12
• Case control (or retrospective) study is an observational study in which people with a disease (cases) are compared with those without it (control group).
o Examples: Patients with mesotheliomas were investigated for exposure to asbestos or other agents; the mothers of children born with birth defects were investigated for an association with drug intake during pregnancy.
• Cross-sectional or prevalence study follows a correlation approach using existing data bases. It is a survey of the frequency of disease, risk factors or other characteristics in a defined population at one particular time.
o Example: The prevalence of diabetes mellitus (diagnosed and undiagnosed) was investigated in an Aboriginal community living in a particular area of metropolitan Sydney.
• Cohort (or prospective) study is also referred to as 'follow up'. The study follows a group (cohort) of individuals with a specified characteristic or disease over a period of time. Comparisons may be made with a control group.
o Example: 120 patients with chronic sciatica were followed over 10 years to determine the outcome of their pain and neurological deficit. These were compared with a matched group who had undergone laminectomy.
• Clinical controlled trial is an experimental study that tests for hypothesised outcomes. An intervention is conducted on a randomly selected group of people and compared with a matched control group not subject to the specific intervention. The objective is to establish a causal relationship between the intervention and the hypothesised outcome. The ideal scientific trial is a double-blind trial. This is the typical study when assessing the outcome of a drug trial as compared with placebo.
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