Changes

====Surveys====

====Surveys====

These are carefully planned studies with clear, specific aims (for example, to estimate the prevalence of disease X in country Y at time Z), which differentiates them from case series studies.  

These are carefully planned studies with clear, specific aims and a defined source population (for example, aiming to estimate the prevalence of disease X in country Y at time Z), which differentiates them from case series studies. Surveys will have a clear sampling strategy and a method of data collection (such as a questionnaire or serological test) used specifically for the study in question. If data regarding both outcomes (such as disease status) and exposures of interest are collected, then the study would be more accurately described as a '''cross sectional analytic study''' (see below).

==Analytic studies==

==Analytic studies==

Analytical studies are used to test hypotheses by comparison of groups of animals based on their exposure or disease status. Analytical studies can be observational or experimental, in observational studies the experimenter does not apply an intervention to the animals or manipulate their environment they simply observe or take measurements.

Analytical studies are used to test hypotheses by comparison of groups of animals based on their exposure or disease status. Analytical studies can be observational or experimental, in observational studies the experimenter does not apply an intervention to the animals or manipulate their environment they simply observe or take measurements.  

===Observational studies===

===Observational studies===