STUDY DESIGNS OBSERVATIONAL STUDIES Dr KHADIJA N ABDULLAH
![STUDY DESIGNS OBSERVATIONAL STUDIES Dr. KHADIJA N. ABDULLAH STUDY DESIGNS OBSERVATIONAL STUDIES Dr. KHADIJA N. ABDULLAH](https://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-1.jpg)
STUDY DESIGNS OBSERVATIONAL STUDIES Dr. KHADIJA N. ABDULLAH
![What is a research design? It is the plan, structure, and strategy of research--the What is a research design? It is the plan, structure, and strategy of research--the](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-2.jpg)
What is a research design? It is the plan, structure, and strategy of research--the blueprint that will guide the research process.
![CLASSIFICATION OF STUDY DESIGNS (cross-sectional) CLASSIFICATION OF STUDY DESIGNS (cross-sectional)](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-3.jpg)
CLASSIFICATION OF STUDY DESIGNS (cross-sectional)
![Descriptive studies Ø Cross-sectional studies can be thought of as providing a snapshot of Descriptive studies Ø Cross-sectional studies can be thought of as providing a snapshot of](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-4.jpg)
Descriptive studies Ø Cross-sectional studies can be thought of as providing a snapshot of the frequency of a disease or other health related characteristics (e. g. exposure variables) in a population at a given point in time. Ø A cross-sectional survey may be purely descriptive and used to assess the burden of a particular condition in a defined population (Prevalence, frequency) and help in planning health services. Ø Descriptive/analytical cross-sectional studies are useful for establishing preliminary evidence for a causal relationship
![No. of men of all ages who smoke in this village No. of men of all ages who smoke in this village](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-5.jpg)
No. of men of all ages who smoke in this village
![Patients at a ward with lung cancer who smoke Patients at a ward with lung cancer who smoke](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-6.jpg)
Patients at a ward with lung cancer who smoke
![Analytical studies A. Cross-sectional • The investigator measures the outcome and the exposure in Analytical studies A. Cross-sectional • The investigator measures the outcome and the exposure in](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-7.jpg)
Analytical studies A. Cross-sectional • The investigator measures the outcome and the exposure in the study participants at the same time. • These studies differ from solely descriptive cross-sectional studies in that they compare the proportion of exposed persons who are diseased with the proportion of non-exposed persons who are diseased.
![lifestyle CHD lifestyle CHD](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-8.jpg)
lifestyle CHD
![Common measures Ø Prevalence Ø Frequencies Common measures Ø Prevalence Ø Frequencies](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-9.jpg)
Common measures Ø Prevalence Ø Frequencies
![Life style CHD present CHD absent Total Not active (P 1) 50 (a) 200 Life style CHD present CHD absent Total Not active (P 1) 50 (a) 200](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-10.jpg)
Life style CHD present CHD absent Total Not active (P 1) 50 (a) 200 (b) 250 Active (P 2) 50 ( c) 700 (d) 750 Total (P) 100 900 1000 P = 100/1000* 100 = 10 % P 1= a/a+b * 100= 50/250 * 100 = 20 % (among subjects not active) P 2= c/c+d* 100= 50/750* 100 = 6. 7 % (among active subjects)
![Analytical studies Analytical studies](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-11.jpg)
Analytical studies
![Measures Ø The odds ratio (OR) is used in case-control studies to estimate the Measures Ø The odds ratio (OR) is used in case-control studies to estimate the](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-12.jpg)
Measures Ø The odds ratio (OR) is used in case-control studies to estimate the strength of the association between exposure and outcome. Ø Case-control studies may prove an association but they do not demonstrate causation.
![](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-13.jpg)
![](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-14.jpg)
![Ø OR of 1. 0 (or close to 1. 0) indicates that the odds Ø OR of 1. 0 (or close to 1. 0) indicates that the odds](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-15.jpg)
Ø OR of 1. 0 (or close to 1. 0) indicates that the odds of exposure among case-patients are the same as, or similar to, the odds of exposure among controls. The exposure is not associated with the disease. Ø Greater than 1. 0 indicates that the odds of exposure among casepatients are greater than the odds of exposure among controls. The exposure might be a risk factor for the disease. Ø Less than 1. 0 indicates that the odds of exposure among casepatients are lower than the odds of exposure among controls. The exposure might be a protective factor against the disease. Ø The magnitude of the odds ratio is called the “strength of the association. ” The further away an odds ratio is from 1. 0, the more likely it is that the relationship between the exposure and the disease is causal.
![Analytical studies *Establishes cause –effect association (temporal association) Analytical studies *Establishes cause –effect association (temporal association)](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-16.jpg)
Analytical studies *Establishes cause –effect association (temporal association)
![Measures: ØIncidence rates ØRelative risk ØAttributable risk Measures: ØIncidence rates ØRelative risk ØAttributable risk](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-17.jpg)
Measures: ØIncidence rates ØRelative risk ØAttributable risk
![Cigarette smoking Developed lung Did not develop cancer lung cancer Total Yes 70 (a) Cigarette smoking Developed lung Did not develop cancer lung cancer Total Yes 70 (a)](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-18.jpg)
Cigarette smoking Developed lung Did not develop cancer lung cancer Total Yes 70 (a) 6930 (b) 7000 (a + b) No 3 (c ) 2997 (d) 3000 (c + d) Incidence rate among smokers = a/a+ b = 70/7000 = 10 per 1000 Incidence rate among non-smokers = c/c + d =3/3000 = 1 per 1000 Relative risk (RR) = Incidence of disease among exposed/ incidence of disease among non-exposed =10/1 = 10 (what does this mean ? ) Attributable risk = incidence among exposed- incidence among non-exposed/ incidence among exposed *100 = 10 -1/10 * 100 = 90 % (what does this mean ? )
![LETS APPLY NOW: 1. Study on breast feeding and IQ 2. Study on vaccination LETS APPLY NOW: 1. Study on breast feeding and IQ 2. Study on vaccination](http://slidetodoc.com/presentation_image_h2/e8fdac1820a625c88e22deba9a988387/image-19.jpg)
LETS APPLY NOW: 1. Study on breast feeding and IQ 2. Study on vaccination 3. Study on fractures among children
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