Scientists use different types of evidence to determine if a drug is safe and can prevent dementia. In some ways, the different types of evidence can be thought of as the characters of a play. Each type serves a distinct role yet some play bigger roles than others in determining the final outcome.
Here are some of the most common types of evidence for prevention:
In a typical trial, people are randomly selected to receive either the drug or a placebo. In a double-blind trial, both the participants and the researchers are "blind" to which person received the drug until after the results are analyzed. Double-blind randomized controlled trials are the "gold-standard" of biomedical research. Unfortunately, they are extremely difficult and expensive for Alzheimer's disease prevention.
In observational research, scientists observe large groups of people to identify traits and choices that associate with disease versus health. These studies can provide cost-effective and detailed information but they must be interpreted with caution.
Different experiments designed to answer the same question will frequently yield different results. The treatment may have been tested in different populations of people, perhaps for different lengths of time or at different doses. Sometimes the results are biased unknowingly by the researchers themselves. Meta-analyses and systematic reviews methodically compile all available research on a given question and then combine them into a single analysis that considers and compares the quality of the methods of each study to draw an overall conclusion.
Experiments in animals and isolated cells are useful for "proof-of-concept" experiments and to help design future research. However, they do not reliably predict whether a treatment is safe or effective in humans.
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