The principles of sampling

• Factors work together and affect physical and mental health
• A disease is a disorder that affects an organism's body, organs, tissues or cells
• Part of Biology (Single Science)
• Epidemiology is the study of the distribution and patterns of health and disease.
• Epidemiology is the study of the distribution and patterns of health and disease, in and across populations.
• Scientists study the incidence of disease, using medical records, and use medical research to investigate causes of disease.
• When investigating health and disease, and risk factors are involved, scientists can't study every person on the planet.
• Scientists must study samples, which are a representative part of a larger quantity.
• Samples must be representative, which means they accurately represent the whole of the group.
• Samples cannot focus on certain groups and ignore others.
• Samples cannot be affected by bias, which is prejudice or favour shown for one person, group, thing or opinion over another.
• To obtain a representative sample, the study must be wide, and cover all groups in the population being studied.
• The study must be random within these groups.
• Sampling might be systematic in that it is carried out at regular time intervals.
• When working with samples of human populations, studies must take account of possible variations owing to differences between the sexes resulting from people of different ages taking part in people's lifestyles, which could affect the study.
• Analyses can be carried out on sub-sets of data within the whole study, so that comparisons can be made within the same age group, for instance.
• In scientific studies, it may be difficult to control lifestyle factors that have the potential to affect the study, particularly if the study is long-term.
• People involved in a long-term study of the effects of alcohol intake, for instance, will have different lifestyle factors, for instance diet and exercise, that could potentially affect the results of the study.
• Data must be adjusted, for instance, to make allowances for the effects of age on rates of disease.