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Observational research methods
Cohort, cross sectional, and case control studies are collectively referred to as observational studies. Often these studies are the only practicable method of studying various problems, for example, studies of aetiology, instances where a randomised controlled trial might be unethical, or if the condition to be studied is rare. Cohort studies are used to study incidence, causes, and prognosis. Because they measure events in chronological order they can be used to distinguish between cause and effect. Cross sectional studies are used to determine prevalence. fake hermes leather handbags They are relatively quick and easy but do not permit distinction between cause and effect. Case controlled studies compare groups retrospectively. They seek to identify possible predictors of outcome and are useful for studying rare diseases or outcomes. They are often used to generate hypotheses that can then be studied via prospective cohort or other studies.research methodscohort studycase control studycross sectional studyCohort, cross sectional, and case control studies are often referred to as observational studies because imitiaton hermes bags the investigator simply observes. No interventions are carried out by the investigator. With the recent emphasis on evidence based medicine and the formation of the Cochrane Database of randomised controlled trials, such studies have been somewhat glibly maligned. However, they remain important because many questions can be efficiently answered by these methods and sometimes they are the only methods available.The objective of most clinical studies is to determine one of the following prevalence, incidence, cause, prognosis, or effect of treatment; it is therefore useful to remember which type of study is most commonly associated with each objective (table 1)View this table:View inlineView popupThe source of the controls should be explained are they from the same population as the sample?Are the controls matched or randomised to minimise bias and confounding.Quality of measurements and outcomesValidity are the measurements used regarded as valid by other investigators?Reproducibility can the results be repeated or is there a reason to suspect they may be a "one off"?Blinded were the investigators or subjects aware of their subject/control allocation?Quality control has the methodology been rigorously adhered to?All studies should be internally valid. That is, the conclusions can be logically drawn from the results produced by an appropriate methodology. For a study to be regarded as valid it must be shown that it has indeed demonstrated what it says it has. A study that is not internally valid should not be published because the findings cannot be accepted.The question of external validity relates to the value of the results of the study to other populations that is, the generalisability of the results. For example, a study showing that 80% of the Swedish population has blond hair, might be used to make a sensible prediction of the incidence of blond hair in other Scandinavian countries, but would be invalid if applied to most other populations.Every published study should contain sufficient information to allow the reader to analyse the data with reference to these key points.In this article each of the three important observational research methods will be discussed with emphasis on their strengths and weaknesses. The investigator then measures a variety of variables that might be relevant to the development of the condition. Over a Different hermes bag fake period of time the people in the sample are observed to see whether they develop the outcome of interest (that is, myocardial infarction).In single cohort studies those people who do not develop the outcome of interest are used as internal controls. The methodology is the same but the study is performed posthoc. The cohort is "followed up" retrospectively. Thus research on risk factors relies heavily on cohort studies.As cohort studies measure potential causes before the outcome has occurred the study can demonstrate that these "causes" preceded the outcome, thereby avoiding the debate as to which is cause and which is effect.A further replica hermes handbags outlet advantage is that a single study can examine various outcome variables. For example, cohort studies of smokers can simultaneously look at deaths from lung, cardiovascular, and cerebrovascular disease. This contrasts with case control studies as they assess only one outcome variable (that is, whatever outcome the cases have entered the study with).
Cohort, cross sectional, and case control studies are collectively referred to as observational studies. Often these studies are the only practicable method of studying various problems, for example, studies of aetiology, instances where a randomised controlled trial might be unethical, or if the condition to be studied is rare. Cohort studies are used to study incidence, causes, and prognosis. Because they measure events in chronological order they can be used to distinguish between cause and effect. Cross sectional studies are used to determine prevalence. fake hermes leather handbags They are relatively quick and easy but do not permit distinction between cause and effect. Case controlled studies compare groups retrospectively. They seek to identify possible predictors of outcome and are useful for studying rare diseases or outcomes. They are often used to generate hypotheses that can then be studied via prospective cohort or other studies.research methodscohort studycase control studycross sectional studyCohort, cross sectional, and case control studies are often referred to as observational studies because imitiaton hermes bags the investigator simply observes. No interventions are carried out by the investigator. With the recent emphasis on evidence based medicine and the formation of the Cochrane Database of randomised controlled trials, such studies have been somewhat glibly maligned. However, they remain important because many questions can be efficiently answered by these methods and sometimes they are the only methods available.The objective of most clinical studies is to determine one of the following prevalence, incidence, cause, prognosis, or effect of treatment; it is therefore useful to remember which type of study is most commonly associated with each objective (table 1)View this table:View inlineView popupThe source of the controls should be explained are they from the same population as the sample?Are the controls matched or randomised to minimise bias and confounding.Quality of measurements and outcomesValidity are the measurements used regarded as valid by other investigators?Reproducibility can the results be repeated or is there a reason to suspect they may be a "one off"?Blinded were the investigators or subjects aware of their subject/control allocation?Quality control has the methodology been rigorously adhered to?All studies should be internally valid. That is, the conclusions can be logically drawn from the results produced by an appropriate methodology. For a study to be regarded as valid it must be shown that it has indeed demonstrated what it says it has. A study that is not internally valid should not be published because the findings cannot be accepted.The question of external validity relates to the value of the results of the study to other populations that is, the generalisability of the results. For example, a study showing that 80% of the Swedish population has blond hair, might be used to make a sensible prediction of the incidence of blond hair in other Scandinavian countries, but would be invalid if applied to most other populations.Every published study should contain sufficient information to allow the reader to analyse the data with reference to these key points.In this article each of the three important observational research methods will be discussed with emphasis on their strengths and weaknesses. The investigator then measures a variety of variables that might be relevant to the development of the condition. Over a Different hermes bag fake period of time the people in the sample are observed to see whether they develop the outcome of interest (that is, myocardial infarction).In single cohort studies those people who do not develop the outcome of interest are used as internal controls. The methodology is the same but the study is performed posthoc. The cohort is "followed up" retrospectively. Thus research on risk factors relies heavily on cohort studies.As cohort studies measure potential causes before the outcome has occurred the study can demonstrate that these "causes" preceded the outcome, thereby avoiding the debate as to which is cause and which is effect.A further replica hermes handbags outlet advantage is that a single study can examine various outcome variables. For example, cohort studies of smokers can simultaneously look at deaths from lung, cardiovascular, and cerebrovascular disease. This contrasts with case control studies as they assess only one outcome variable (that is, whatever outcome the cases have entered the study with).
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