What are ethical aspects you see from the study? Case 2.
19. What are ethical aspects you see from the study? Case 2.
Family planning services throughout all villages are needed to decrease birth rate in Indonesia. In Ayodya Province, almost all reproductive couples chose the vasectomy
method. Since the users were high in demand while the doctors in that province were limited, dr. Nyoman Abimanyu, a surgeon who was also the head of the Provincial Health
Department, trained a group of nurses to be able to conduct vasectomies. With his authorization for the nurses to do vasectomies, dr. Abimanyu got a lot of criticisms from
other surgeons. Therefore, he thought that it was important to have empiric data from a research.
In his study, a number of candidate acceptors candidate users were vasectomised by trained nurses, while the other users underwent vasectomies by doctors. Previously, all
candidates were informed whether they would be operated by doctors or trained nurses. The number of samples was already sufficient and was already sampled randomly to
ensure representatives for their population. The results are as follows: vasectomy failure on the group operated by nurses was 2 while by doctors was 1.25. Hematoma
subcutaneous bleeding in the nurses’ group was 8 and in the doctors’ group was 5.
Learning Tasks 2:
1.
What are dependent and independent variables in that study?
2.
Is the study above an observational or experimental study?
3.
What is the intervention?
4.
Is that possible to randomize?
5.
What randomization can be done?
6.
What are the advantages and disadvantages of each randomization method?
7.
Is it possible to do cross-over design? If not, why?
8.
Is it possible to do blind design?
9.
Which blind design can be done?
10.
From the result above, what is the conclusion? Which is more effective?
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11.
If the result is as follows, what is the conclusion? Which one is more effective? The vasectomy failure in the group operated by nurses is 2 while on the doctor is
1.25 p 0.01. Hematoma subcutaneous bleeding in the nurses’ group is 8 and in the doctors’ group is 5 p 0.01.
Self Assessments: 1. Describe the application of clinical trials in diagnosis and patient treatment?
2. Describe the design of parallel clinical trials and cross-over trials 4. Explain the purpose and application of parallel clinical trials and cross-over trials
5. Describe the definition and purpose of single blind and double blind study. 6. Describe the definition of informed consent.
7. On the British Medical Journal 2002, the study was conducted to know the effect of ice consumption to headache with the design study was prospective
randomized trial Source: UKDI Headache +
Headache - Total
Accelerated eating group 20
53 73
Cautious eating group 9
63 72
Total 29
116 145
What is the role of the risk factor? A. 2,9
B. 2,2 C. 4,4
D. 4,6 E. 6,8
13. On the study of medication that will be use to suppress cholesterol level; the study procedure was dividing the study group in to two: control and intervention group.
Then, the outcome will be compared for both groups. What is the design of the study? Source: UKDI
A. True experimental B. Quasi experimental
C. Cross sectional D. Cohort
E. Descriptive
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M O D U L E ~ 17
Reference Greenberg, p. 127-136
Epidemiology Study Design: Diagnostic Test
dr. Gede Artawan Eka Putra, M. Epid dr. Anak Agung Sagung Sawitri, MPH
AIMS:
To be able to describe validity and reliability of certain test to apply in the individual and or community context
LEARNING OUTCOMES:
1. To describe definition of accuracy, validity and reliability 2. To explain parameters used to indicate validity and reliability
3. To describe concept of test validity of the continues or multilevel outcome result 4. To choose ideal diagnostic test in certain situations related to individual and
community context
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CURRICULUM CONTENTS:
1. Definition of diagnostic test and screening program 2. Accuracy, validity sensitivity, specificity, predictive value, and likely hood ratio and
reliability 3. Screening program
ABSTRACTS
All clinical information is subject to error. Accounting for the various errors that can arise in diagnostic testing allows the physician to select tests and interpret the result of those
tests appropriately. The errors are false- negative, false-positive.
Sensitivity and specificity are characteristics of a diagnostic test. It is useful to
consider two other measures, positive predictive value PV+ and negative predictive value PV-, which are use to interpret the results of a diagnostic test.
For multilevel or continuous outcome test results, a dividing line or cut off point
can be chosen to separate findings considered to be positive or negative. The performance of diagnostic tests also can be assessed by use of likelihood ratios.
SELF DIRECTING LEARNING
Basic knowledge and its application that students must know include: 1. Accuracy
2. Sensitivity, specificity, predictive value, likelihood ratio 3. Cut off point
4. Screening program
SCENARIO LEARNING TASK
Case 1
The result of screening test was as bellow; Diabetic retinopathy
Sakit Tidak Sakit
Total Positif
3.200 1.400
4.600 Negatif
150 29.000
29.150 Total
3.350 30.400
33.750
Learning Tasks 1
1. Calculate the sensitivity, specificity, and predictive value of diabetic retinopathy and Interpret each of your calculation
2. What is the prevalence of diabetic retinopathy among the population?
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3. What is the relation between prevalence and predictive value? What is the relation with the target group for screening program?
4. When you conduct screening test among elderly population, which prevention you have done: primary, secondary, or tertiary?
Case 2
A detailer has come to dr. Arjuna for offering cheap rapid test for anemia. Dr. Arjuna asked 3 tests for trial. Fortunately, Mrs. Drupadi came for consultation of malaise and
continuing dizziness. Dr. Arjuna asked permission from mrs. Drupadi to take the blood sample for checking anemia. At the same time, he also told her that he wanted to check
the rapid test for anemia. Using cyan-met HB, the result of hemoglobin was 12.5mg, while the result of rapid test
respectively was 10.5 mg; 10.2mg; and 12.0mg.
Learning Task 2
If the criteria of anemia was 11 mg, how you conclude the result of the rapid test for anemia that just being tried by dr. Arjuna?
Self Assessments:
1. What is the definition of sensitivity?
2. What is the definition of specificity?
3. If the prevalence increases, what other value will also increase?
4. If the prevalence of a certain disease is high, while the sensitivity and specificity
are stable, than ................... will be low.
M O D U L E ~ 18
Reference Mausner Bahn, p. 91-110, Greenberg 141-153
Variability and Biases
dr. Anak Agung Sagung Sawitri, MPH
Dr. dr. Gd Indraguna Pinatih, MSc., Sp.GK
AIMS:
Be able to describe variability and biases those might occurred in certain studies
LEARNING OUTCOMES:
1. To describe the concept of patient variability, variability in medical research,
variability of measurement, both in individual and population level.
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2. To explain internal validity, external validity, selection bias, information bias, and
confounding factors. 3.
To describe sources of bias in descriptive research design, cross-sectional, case- control, cohort, and clinical trials and describe how to minimize those biases
CURRICULUM CONTENTS:
1. Variability individual, measurement, and population
2. Validity internal and external
3. Biases selection bias, information bias, and confounding bias
ABSTRACTS
In this lecture, the topics of variability and bias systematic errors in epidemiologic measurements are discussed. A distinction is drawn between random
variation which is inversely related to precision in measurement, and non random or systematic error, which is related to distortion in measurement.
Variability can arise from 1 the subject under study, 2 differences between
individuals, 3 the approach used to sample subjects, or 4 the measurement process itself. Variability related to sampling is likely to diminish as the sample size increases.
With extremely large sample size, a very small difference in outcome between study groups can be statistically significant. Whether the magnitude of this difference is
sufficient to warrant a change in clinical practice is separate, but equally important question.
Validity concerns the extent to which the findings of a study reflect truth. Internal validity relates to the accuracy of study findings for the persons who are investigated.
External validity concerns the extent to which study findings accurately apply to persons who are not studied.
Bias is defined as lack of validity. Conventionally, bias is classified into three major types: selection bias, information misclassification bias, and confounding.
Selection bias refers to the introduction of systematic errors into study results through the manner in which study subjects are selected. Information bias results in systematic
errors in study findings that originate in the approach to collecting information. Two kinds of information bias can exist. Non-differential misclassification occurs when errors in the
information about one variable unrelated to the status of another variable. Differential misclassification, on the other hand, occurs when errors in the information about one
variable are affected by the status of another variable.
Confounding is concerned with the mixing of the primary effect of interest with
the effects of one or more extraneous factors. In experimental studies, the problem of confounding is reduced by randomization, which tends to balance the study groups with
respect to both known and unknown determinants of the outcome. In observational research, however, study groups may differ appreciably in factors that are 1 related to
the risk of disease among unexposed persons and 2 are also associated with the exposure of interest, but not as a result of being exposed. The influence of these
potential confounders can be addressed in the study design e.g., through matching or
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restrictive inclusion criteria or in the analysis e.g., through stratification or regression techniques. Only known confounders can be addressed in observational research.
No study is immune from the possibility of bias. The investigator must therefore consider potential sources of bias when sampling subjects, collecting information,
analyzing results, and interpreting findings. With planning and forethought, it is possible to anticipate and avoid certain types of error and thus conduct a study that leads to a
convincing and valid conclusion
SELF DIRECTING LEARNING
Basic knowledge and its application that students must know include: 1. Variability
2. Validity 3. Bias
4. Confounding
SCENARIO LEARNING TASK
1.
Carefully look at Patient Profile in Greenberg page 141. What possibilities may cause the differences in the patient’s cholesterol level?
2. Explain the differences between random and systematic variation bias by drawing
a figure as shown in Greenberg page 142 Figure 10.1
3. Draw a copy of Figure 10-2 in Greenberg page 143 into your work-paper, and then
explain with your own words about the definition of sampling variability in research studies. From that example it can be concluded that a smaller sample size in a
research study, will cause the variability to be ……………...
4. Draw a copy of Figure 10-3 in Greenberg page 143 into your work-paper.
a. What is demonstrated in A and the B of the study figure? b. From that example, it can be concluded that the consequence of a bigger
sample size in a research study is ……………. c. In a research study like the one above, despite sample size or differences
which statistically give significant results, what other things are very important in biological or clinical meaning?
5. Explain with examples, the differences between internal and external validity.
6. Give examples of selection bias.
7. Information bias may be presented in two forms, which are nondifferential
misclassification and differential misclassification. Explain those differences using examples.
8. Draw a copy of figure 10-7 in Greenberg page 148 into your work-paper. Ex-plain,
with the above examples, nondifferential misclassification which causes underestimated OR and differential misclassification which causes overestimated
OR.
9. a. Explain the definition of confounding variable
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b. Two methods to control the effect of confounding variables are …… ………………
c. Carefully see Figure 10-9 in Greenberg page 150. Calculate the OR for all subjects, OR for the obese group, and OR for the non-obese group. What is
your conclusion after calculating those three ORs? d. The method used above no. c controls the effect of confounding variables by
…
Self Assessments: 1. Explain the concept of variability in one patient and in medical research.
2. Explain individual population variability, variability related to measurement, 3. Explain the definition of validity and bias.
4. Explain the difference between internal validity and external validity. 5. What is the difference between selection bias, information bias, and confounding
bias?