SMHS ExpObsStudies - Revision history

Glenbrau: /* Degree of usefulness and reliability */

2015-04-27T15:30:09Z

‎Degree of usefulness and reliability

Glenbrau: /* Types of observational studies */

2015-04-27T15:29:13Z

‎Types of observational studies

Glenbrau: /* Types of experimental studies */

2015-04-27T15:28:37Z

‎Types of experimental studies

Dinov: /* Problems */

2014-09-11T20:27:28Z

‎Problems

Dinov: /* Problems */

2014-09-11T20:27:03Z

‎Problems

Dinov: /* Theory */

2014-09-11T20:25:30Z

‎Theory

Show changes

Liyufang: /* References */

2014-08-29T16:51:57Z

‎References

Clgalla: /* Theory */

2014-08-01T16:32:36Z

‎Theory

Clgalla: /* Theory */

2014-08-01T16:30:46Z

‎Theory

Clgalla at 16:30, 1 August 2014

2014-08-01T16:30:20Z

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 =====Degree of usefulness and reliability=====
 Although observational studies can’t be used as reliable sources to make statements of fact about the ‘safety, efficacy, or effectiveness’ of a practice, they can still be used to:
-*Provide information on real world use and practice;
+*Provide information on real world use and practice
-*Detect signals about the benefits and risk of use in the general population;
+*Detect signals about the benefits and risk of use in the general population
-*Help formulate hypotheses to be tested in subsequent experiments;
+*Help formulate hypotheses to be tested in subsequent experiments
-*Provide part of the community-level data needed to design more informative pragmatic clinical trials;
+*Provide part of the community-level data needed to design more informative pragmatic clinical trials
-*Inform clinical practice.
+*Inform clinical practice
 ====Bias and compensating methods====

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 Observational Study draws inferences about the possible effect of a treatment on subjects where the assignment of subjects into a treated group versus a control group is outside the control of the investigator.
 =====Types of observational studies=====
-*Case-control study: originally developed in epidemiology, where two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute.
+*''Case-control study'': Originally developed in epidemiology, where two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute.
-*Cross-sectional study: involves data collection from a population, or a representative subset, at one specific point in time.
+*''Cross-sectional study'': Involves data collection from a population, or a representative subset, at one specific point in time.
-*Longitudinal study: correlational research study that involves repeated observations of the same variables over long periods of time.
+*''Longitudinal study'': Correlational research study that involves repeated observations of the same variables over long periods of time.
-*Cohort study (panel study): a particular form of longitudinal study where a group of patients is closely monitored over a span of time.
+*''Cohort study (panel study)'': A particular form of longitudinal study where a group of patients is closely monitored over a span of time.
-*Ecological study: an observational study in which at least one variable is measured at the group level.
+*''Ecological study'': An observational study in which at least one variable is measured at the group level.
 =====Degree of usefulness and reliability=====

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 Experimental study is an empirical method that arbitrates between models or hypothesis and used to test existing theories or new hypotheses in order to support them or disprove them. Controlled experiments provide researches with insight into the causal relationship by demonstrating what outcome occurs when a particular factor is manipulated. Experiments may vary from personal and informal natural comparisons, to highly controlled ones.
 =====Types of experimental studies=====
-*Controlled experiments: compare the results obtained form experimental samples against control samples, which are practically identical to the experimental sample except for the one whose effect is being tested.
+*''Controlled experiments'': Compare the results obtained form experimental samples against control samples, which are practically identical to the experimental sample except for the one whose effect is being tested.
-*Natural experiments: rely solely on observations of the variables of the system under study, rather than manipulation of just one or a few variables as occurs in controlled experiments.
+*''Natural experiments'': Rely solely on observations of the variables of the system under study, rather than manipulation of just one or a few variables as occurs in controlled experiments.
-*Field experiments: named to draw a contrast with laboratory experiments, which enforce scientific control by testing a hypothesis in the artificial and highly controlled setting of a laboratory. It is often used in social sciences, and especially in economic analyses o education.
+*''Field experiments'': Named to draw a contrast with laboratory experiments, which enforce scientific control by testing a hypothesis in the artificial and highly controlled setting of a laboratory. It is often used in social sciences, and especially in economic analyses of education.
 ====Observational Study====

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 # Now being impressed by cohort studies, you decide to recruit the current student body of UM SPH to prospectively study exercise as a risk factor for many diseases. One of your friends asks if they can use your data to study exercise as a risk factor for MERRF syndrome, an extremely rare disease of the mitochondria with an estimated prevalence of 9 per 1,000,000. Why or why not might this be a good idea?
 # Your real interest is maternal fitness level during pregnancy and cardiovascular disease of the offspring in adulthood. What might be the challenges that you will face in conducting a cohort study to answer this question?
 The next six problems are based on the following article:
@@ Line 73: / Line 74: @@
   low-fat dairy products and with reduced saturated and total fat. Sodium intake
   and body weight were maintained at constant levels.
-−
   Results
   At base line, the mean (+/-SD) systolic and diastolic blood pressures were

@@ Line 55: / Line 55: @@
 # Now being impressed by cohort studies, you decide to recruit the current student body of UM SPH to prospectively study exercise as a risk factor for many diseases. One of your friends asks if they can use your data to study exercise as a risk factor for MERRF syndrome, an extremely rare disease of the mitochondria with an estimated prevalence of 9 per 1,000,000. Why or why not might this be a good idea?
 # Your real interest is maternal fitness level during pregnancy and cardiovascular disease of the offspring in adulthood. What might be the challenges that you will face in conducting a cohort study to answer this question?
 The next six problems are based on the following article:
 Abstract from [http://www.nejm.org/doi/full/10.1056/NEJM199704173361601 DOI: 10.1056/NEJM199704173361601 (Appel et al. 1997)].
   Background
-  It is known that obesity, sodium intake, and alcohol consumption factors influence blood pressure. In this clinical trial, Dietary Approaches to Stop  Hypertension, we assessed the effects of dietary patterns on blood pressure.
+  It is known that obesity, sodium intake, and alcohol consumption factors
   Methods
-  We enrolled 459 adults with systolic blood pressures of less than 160 mm Hg and diastolic blood pressures of 80 to 95 mm Hg. For three weeks, the subjects were fed a control diet that was low in fruits, vegetables, and dairy products, with a fat content typical of the average diet in the United States. They were then randomly assigned to receive for eight weeks the control diet, a diet rich in fruits and vegetables, or a "combination" diet rich in fruits, vegetables, and low-fat dairy products and with reduced saturated and total fat. Sodium intake and body weight were maintained at constant levels.
+  We enrolled 459 adults with systolic blood pressures of less than 160 mm Hg
   Results
-  At base line, the mean (+/-SD) systolic and diastolic blood pressures were 131.3 $\pm$ 10.8 mm Hg and 84.7 $\pm$ 4.7 mm Hg, respectively. The combination diet reduced systolic and diastolic blood pressure by 5.5 and 3.0 mm Hg more, respectively, than the control diet (P<0.001 for each); the fruits-and-vegetables diet reduced systolic blood pressure by 2.8 mm Hg more (P<0.001) and diastolic blood pressure by 1.1 mm Hg more than the control diet (P=0.07). Among the 133 subjects with hypertension (systolic pressure, > or =140 mm Hg; diastolic pressure, > or =90 mm Hg; or both), the combination diet reduced systolic and diastolic blood pressure by 11.4 and 5.5 mm Hg more, respectively, than the control diet (P<0.001 for each); among the 326 subjects without hypertension, the corresponding reductions were 3.5 mm Hg (P<0.001) and 2.1 mm Hg (P=0.003).
+  At base line, the mean (+/-SD) systolic and diastolic blood pressures were
   Conclusions
-  A diet rich in fruits, vegetables, and low-fat dairy foods and with reduced saturated and total fat can substantially lower blood pressure. This diet offers an additional nutritional approach to preventing and treating hypertension.
+  A diet rich in fruits, vegetables, and low-fat dairy foods and with reduced
 # What type of study is this?

@@ Line 83: / Line 83: @@
 ===References===
-*[http://mirlyn.lib.umich.edu/Record/004199238 Statistical inference Casella, G. & Berger, R.]
+*[http://www.public.iastate.edu/~dnett/S401/nexpvsobs.pdf  Online resource]
-*[http://mirlyn.lib.umich.edu/Record/004232056 Sampling Thompson, S.]
+*[http://en.wikipedia.org/wiki/Experiment   Experiment Wikipedia]
-*[http://mirlyn.lib.umich.edu/Record/004133572 Sampling theory and methods Sampath,S.]
+*[http://en.wikipedia.org/wiki/Observational_study  Observational Study Wikipedia]

@@ Line 24: / Line 24: @@
 **Ecological study: an observational study in which at least one variable is measured at the group level.
-*'''Degree of usefulness and reliability:''' though observational studies can’t be used as reliable sources to make statements of fact about the ‘safety, efficacy, or effectiveness’ of a practice, they can still be used for:
+*'''Degree of usefulness and reliability:''' though observational studies can’t be used as reliable sources to make statements of fact about the ‘safety, efficacy, or effectiveness’ of a practice, they can still be used to:
-*(1) provide information on real world use and practice;
+**Provide information on real world use and practice;
-*(2) detect signals about the benefits and risk of use in the general population;
+**Detect signals about the benefits and risk of use in the general population;
-*(3) help formulate hypotheses to be tested in subsequent experiments;
+**Help formulate hypotheses to be tested in subsequent experiments;
-*(4) provide part of the community-level data needed to design more informative pragmatic clinical trials; (5) inform clinical practice.
+**Provide part of the community-level data needed to design more informative pragmatic clinical trials;
 *'''Bias and compensating methods:'''

@@ Line 15: / Line 15: @@
 **Field experiments: named to draw a contrast with laboratory experiments, which enforce scientific control by testing a hypothesis in the artificial and highly controlled setting of a laboratory. It is often used in social sciences, and especially in economic analyses o education.
 Observational Study draws inferences about the possible effect of a treatment on subjects where the assignment of subjects into a treated group versus a control group is outside the control of the investigator.
 *'''Types of observational studies:'''
@@ Line 22: / Line 23: @@
 **Cohort study (panel study): a particular form of longitudinal study where a group of patients is closely monitored over a span of time.
 **Ecological study: an observational study in which at least one variable is measured at the group level.
 *'''Degree of usefulness and reliability:''' though observational studies can’t be used as reliable sources to make statements of fact about the ‘safety, efficacy, or effectiveness’ of a practice, they can still be used for:
@@ Line 28: / Line 30: @@
 *(3) help formulate hypotheses to be tested in subsequent experiments;
 *(4) provide part of the community-level data needed to design more informative pragmatic clinical trials; (5) inform clinical practice.
 *'''Bias and compensating methods:'''
 When a randomized experiment cannot be carried out, the alternative line of investigation suffers from the problem that the decision of which subjects receive the treatment is not entirely random and thus is a potential source of bias. A major challenge in conducting observational studies is to draw inferences that are acceptably free from influences by overt biases, as well as to assess the influence of potential hidden biases. An observer of an uncontrolled experiment records potential factors and the data output: the goal is to determine the effects of the factors. Sometimes the recorded factors may not be directly causing the differences in the output. Also, recorded or unrecorded factors may be correlated which may yield incorrect conclusions. Finally, as the number of recorded factors increases, the likelihood increases that at least one of the recorded factors will be highly correlated with the data output simply by chance.
 *'''Comparisons between experimental and observational studies:'''