Midterm #2

Question 1

Which study designs can be either retrospective or prospective?

Answer 1

Cohort

Question 2

Describe how participants are selected for cross-sectional and case-control studies.

Answer 2

choose groups with (cases) and without (controls) the outcome of interest and look back at what different exposures they may have had to identify possible risk factors. Case control studies have been widely used in genetic studies to identify susceptibility genes and are the best design to study rare conditions, as they are efficient in use of time and money, collecting a lot of relevant information on targeted individuals. Case control studies may be “nested” within cohort studies.

Question 3

Describe the impact of sampling with respect to case-control and cross-sectional studies.

Answer 3

• retrospective
• tells you what happened.
• not proactive
• Case-control studies are commonly used when the route of exposure is unknown and there is not a clearly defined group of people that can be identified as exposed and unexposed. In these studies, cases are individuals that have the disease and controls are those that do not have the disease

Question 4

Provide 5 research questions that you would answer with a cross-sectional study.

Answer 4

-prevalence of x at a period of time

Question 5

Provide 5 research questions that you would answer with a case-control study.

Answer 5

• dividing people by disease/no disease
• seeing how another variable impacts each person.

ex. This study used a matched design, matching infants who had persistent pulmonary hypertension with infants who did not have it, and compared the rates of exposure to SSRIs.
ex. This study matched patients with non-Hodgkin lymphoma (NHL) with control subjects and compared their history of autoimmune and chronic inflammatory disorders, markers of severity, and treatment. It found that the risk of NHL was increased in association with rheumatoid arthritis, primary Sjögren syndrome, systemic lupus erythematosus, and celiac disease.
ex. This study looked at the relation between risk of acute myocardial infarction and current or former smoking, type of tobacco, amount smoked, effect of smokeless tobacco, and exposure to secondhand smoke

Question 6

What are the primary sources of bias in case-control studies?

Answer 6

-Because the disease and exposure have already occurred at the outset of a case control study, there may be differential reporting of exposure information between cases and controls based on their disease status. For example, cases and controls may recall past exposure differently (recall bias). Similarly, the recording of exposure information may vary depending on the investigator’s knowledge of an individual’s disease status (interviewer/observer bias). Therefore, the design and conduct of the study must be carefully considered, as there are limited options for the control of bias during the analysis. Selection bias in case-control studies Selection bias is a particular problem inherent in case-control studies, where it gives rise to non-comparability between cases and controls. Selection bias in case control studies may occur when: ‘cases (or controls) are included in (or excluded from) a study because of some characteristic they exhibit which is related to exposure to the risk factor under evaluation’ [1]. The aim of a case-control study is to select study controls who are representative of the population which produced the cases. Controls are used to provide an estimate of the exposure rate in the population. Therefore, selection bias may occur when those individuals selected as controls are unrepresentative of the population that produced the cases.

Question 7

Describe each source of bias.

Answer 7

information bias
selection bias
confounding

Question 8

Practice changing latency, induction, and interview times and consider the potential impact of bias on study results.

Answer 8

?

Question 9

What is a study design?

Answer 9

Process wherein methods and procedures to conduct a study are organised.

Study designs serve different objectives. They have different key features and components.

Question 10

Why is it important to pay attention to the study design ?

Answer 10

Study design probes the way a study was/is/will be conducted.

It informs us about study’s methodology, strengths and vulnerabilities.

Study-design defects can lead to bias (e.g. systematic error, confounding).

Question 11

Types of study

Answer 11

Observational and experimental

Question 12

Types of observational study

Answer 12

cross-section
case-control
cohort studies

Question 13

types of experimental study

Answer 13

randomized controlled trials

Quasi-experimental design

Question 14

CROSS-SECTIONAL STUDIES

sample?

Answer 14

Cross-sectional studies provide a snapshot of disease status in a population at one point in time*.
No recurrences, data –disease and exposure- are collected once.

Participants:
Selection of the participants is generally based on
random (equal probability) or probability samples (known probability)

Question 15

CROSS SECTIONAL STUDIES Measures of association:

Answer 15

• Prevalence differences

- prevalence- odds ratio

Question 16

strengths of using cross-sectional study

Answer 16

Snapshot of population parameters (e.g. prevalence)

Occurrence of disease

Cost and time efficiency

Invulnerability to attrition (loss to follow

Question 17

limitations of cross-sectional studies

Answer 17

Doesn’t aim for causal reasoning

Doesn’t allow to determine risk

Not appropriate to study rare diseases or exposures

Insensitive to variations (e.g. seasonality)

Generally based on self-reported measures

Question 18

Cohort Studies definition

participants

Answer 18

Case-control studies aim to evaluate – or to generate - hypotheses about disease etiology (Association between risk factors and diseases).
Cases and controls are selected in the present and then assessed retrospectively

Participants are selected based on their disease status
Cases: People who have the diseases
Controls: People who do not have the disease

Question 19

cohort studies, selection of participants

Answer 19

cases and controls

• controls can be difficult to find something that is a valid estimation
• selection must not depend on exposure

Question 20

cohort measures of association

Answer 20

-odds ratio, relative to control

Question 21

strengths of case-control studys

Answer 21

Appropriate to study causality

Allow to study multiple exposures.

Long induction and latency periods can be studied (retrospective study)

Efficient and inexpensive

Appropriate for rare diseases

Question 22

limitations of case-control studys

Answer 22

Vulnerable to selection bias

Vulnerable to misclassification bias

Subject to recall bias

Inefficient for rare exposures

Limited on estimation (e.g. no prevalence)

Only allow to study one disease at the time

Disadvantages
Retrospective studies have more problems with data quality because they rely on memory and people with a condition will be more motivated to recall risk factors (also called recall bias).
Not good for evaluating diagnostic tests because it’s already clear that the cases have the condition and the controls do not
It can be difficult to find a suitable control group

Question 23

Information bias

Answer 23

Information bias results from systematic differences in the way data on exposure or outcome are obtained from the various study groups.1 This may mean that individuals are assigned to the wrong outcome category, leading to an incorrect estimate of the association between exposure and outcome.

Errors in measurement are also known as misclassifications, and the magnitude of the effect of bias depends on the type of misclassification that has occurred. There are two types of misclassification – differential and non-differential – and these are dealt with elsewhere (see “Sources of variation, its measurement and control”).

Question 24

Observer bias

Answer 24

may be a result of the investigator’s prior knowledge of the hypothesis under investigation or knowledge of an individual’s exposure or disease status. Such information may influence the way information is collected, measured or interpretation by the investigator for each of the study groups.

For example, in a trial of a new medication to treat hypertension, if the investigator is aware which treatment arm participants were allocated to, this may influence their reading of blood pressure measurements. Observers may underestimate the blood pressure in those who have been treated, and overestimate it in those in the control group.

Question 25

Interviewer bias

Answer 25

occurs where an interviewer asks leading questions that may systematically influence the responses given by interviewees.

Minimising observer / interviewer bias:

Where possible, observers should be blinded to the exposure and disease status of the individual
Blind observers to the hypothesis under investigation.
In a randomised controlled trial blind investigators and participants to treatment and control group (double-blinding).
Development of a protocol for the collection, measurement and interpretation of information.
Use of standardised questionnaires or calibrated instruments, such as sphygmomanometers.
Training of interviewers.

Question 26

Recall (or response) bias

Answer 26

In a case-control study data on exposure is collected retrospectively. The quality of the data is therefore determined to a large extent on the patient’s ability to accurately recall past exposures. Recall bias may occur when the information provided on exposure differs between the cases and controls. For example an individual with the outcome under investigation (case) may report their exposure experience differently than an individual without the outcome (control) under investigation.

Recall bias may result in either an underestimate or overestimate of the association between exposure and outcome.

Methods to minimise recall bias include:

Collecting exposure data from work or medical records.
Blinding participants to the study hypothesis.

Question 27

Social desirability bias

Answer 27

occurs where respondents to surveys tend to answer in a manner they feel will be seen as favourable by others, for example by over-reporting positive behaviours or under-reporting undesirable ones. In reporting bias, individuals may selectively suppress or reveal information, for similar reasons (for example, around smoking history). Reporting bias can also refer to selective outcome reporting by study authors.

Question 28

Performance bias

Answer 28

refers to when study personnel or participants modify their behaviour / responses where they are aware of group allocations.

Question 29

Detection bias

Answer 29

occurs where the way in which outcome information is collected differs between groups.

Question 30

Instrument bias

Answer 30

refers to where an inadequately calibrated measuring instrument systematically over/underestimates measurement. Blinding of outcome assessors and the use of standardised, calibrated instruments may reduce the risk of this.

Question 31

what is the Mantel-Haenszel Odds Ratio

Answer 31

The Cochran-Mantel-Haenszel method is a technique that generates an estimate of an association between an exposure and an outcome after adjusting for or taking into account confounding. The method is used with a dichotomous outcome variable and a dichotomous risk factor.

Question 32

types of study design ( the tree)

Answer 32

can be observational or experimental.

observational:
- cross section
- case control
- cohort studies

experimental:

• randomized controlled trials
• quasi-experimental design

Question 33

observational vs experimental

Answer 33

observational observes without assigning treatment. Observational, the treatment that each
subject receives is determined beyond the
control of the investigator.

experimental applies a treatment then assesses treatment from experiment.

Question 34

types of observational studies

Answer 34

• case-controlled
• cohort
• cross sectional

Question 35

describe cohort study

Answer 35

groups studied, example being people who wore suncreen and who didn’t then assessing them.

• people who work and who don’t work and likihood to buy cigarettes/start smoking
• so basically pre-set cohorts

Question 36

6 ways to control confounding

Answer 36

randomization
stratification
matching
modelling
standardization
restriction