4/5/6. Analytical Case Control Studies & Cohort Studies & Other Types of Studies

what type of study?

Compares diseased individuals to non-diseased individuals – in relation to exposure status

case-control study

• Cases – have the outcome of interest

• Controls or non-cases – do not have the outcome

what are case control studies in relation to time?

retrospective (Start in present time and go back in time to evaluate risk factor exposure)

What type of study?

We measure the odds of disease among exposed versus odds of exposure among those with disease versus those without disease

case-control study

In case control studies, at the start of the study, the disease or outcome has not/already occurred, and cases and controls are grouped based on …?

has already occurred; the outcome/disease status

in case-control studies, has the disease/outcome already occurred at the start of the study?

yes. cases and controls are grouped based on the outcome/disease status

how are controls selected in case-control studies?

• selected from same community, location, or hospital

• similar characteristics as cases except for disease status

• evaluate exposure info in controls in same manner as cases

In a __________ study in this sample say you want evaluate the variables that may have contributed to children wearing eye- glasses. So we can compare the children with eye-glasses (case group) to children not wearing eye-glasses (control group). We can retrospectively collect information family history, medical history, tv-watching, etc. We can then evaluate the odds of these possible risk factors to the outcome of children wearing eye-glasses (outcome could be astigmatism, myopia)

case-control

Association between exposure-outcome can be evaluated by estimating…?

odds ratios

how is odds ratio calculated?

Odds ratios are estimated based on the probability of disease among exposed individuals relative to the probability of disease among unexposed individuals.

what are the advantages of case-control studies?

• Efficient in design

• Shorter duration

• Less expensive

• Convenient for studying many exposures

• Efficient for rare diseases and for diseases with long latency period

• Measures of association can be calculated to evaluate exposure-outcome relationship (odds ratio)

what are the disadvantages of case-control studies?

• retrospective nature makes it difficult to establish time sequence of exposure-outcome relationship

• potential bias

what are different sources of bias?

• recall bias

• interview bias

• reporting bias

• misclassification bias

what type of bias?

Cases recall information differently when compared to controls

recall bias (can occur in case-control and cross-sectional studies)

what is the most common type of bias in case-control studies?

recall bias

• Cases remember and report their previous exposure experience differently from controls

• Ex: Moms of children with orofacial clefts recall risks more accurately

what type of bias?

Differences that occur in the recording or interpretation of information from participants

interviewer bias

what type of bias?

Ex: Those with periodontal disease are examined more frequently to evaluate oral health status versus those without

interviewer bias

what type of bias?

Those who smoke are interviewed more to evaluate oral health status versus those who do not smoke

interviewer bias

what study designs can interviewer bias occur in?

Cross-sectional, Case-control and cohort studies: Knowledge of a subject’s disease status or exposure status may lead to increased questioning by the interviewer

what type of bias?

• Under-reporting of socially undesirable behaviors (Smoking, drinking)

• Over-reporting (Exposure to chemicals, fluoride in water)

• Cases may refuse to answer sensitive questions (Substance abuse)

reporting bias

misclassification bias is most common in what study design?

case-control studies

what type of study design can reporting bias occur in?

cross-sectional, case-control, cohort studies

what type of bias?

• Inaccurate case definitions or inclusion/exclusion criteria

• Participants are incorrectly ‘assigned’ or categorized into the wrong exposure or outcome group

• Can lead to diluted or exaggerated effects

misclassification bias

in relation to time, how are cross-sectional studies assessed?

at a point in time (slice of time)

• temporality cannot be established

in relation to time, how are case-control studies assessed?

retrospectively

cohort studies are also called…?

prospective or longitudinal studies

what is a cohort?

any designated group of individuals

describe how a cohort study is designed.

1. Start with a group of people and identify an exposure.

2. Divide the cohort into exposed and unexposed groups (Smokers versus non-smokers).

3. Follow them over a period of time to observe the outcome (periodontal disease).

4. At the end of the study determine incidence of outcome among exposed versus unexposed

cohort study

can time sequence of events (temporality) be established in cohort study?

yes (due to prospective nature)

what measures can be calculated during cohort studies?

incidence (proportions) and incidence rates

describe cohort studies in relation to time.

prospective

what are advantages of cohort studies?

• similar efficiency to RCT

• more ethical than clinical trials

• good for rare exposures (pesticides, cancer)

• look at multiple outcomes due to single exposure

• estimate incidence rates over time

• establish temporality and causality

what are disadvantages of cohort studies?

• NOT efficient for rare diseases

• long duration (time, money)

• additional resources needed

• exposure status may change over time (smoking/drink patterns)

• prone to loss (follow-up bias)

in case-control studies, participants are grouped by…?

disease status

in cohort studies, participants are grouped by…?

exposure status

what type of study?

• Participants are grouped by disease status

• Utilizes less time and money

• Can be used for rare diseases

• Multiple exposures can be studied

• Does not work well for rare exposures

• Prone to recall bias/information bias

case-control studies

what type of study?

• Participants are grouped by exposure status

• Long duration of follow-up so utilizes more time and resources

• Can be used for rare exposures

• Multiple outcomes can be evaluated

• May not work well for rare diseases

• Prone to loss to follow-up bias due to dropouts

cohort studies

what type of study design?

A detailed review of published articles on a particular research question

systematic reviews

in systematic reviews, what components must be clearly defined?

• search criteria

• inclusion/exclusion criteria

• time period

what are advantages of systematic reviews?

• summarize info from different sources

• broadly generalized results

• more reliable than individual sutides

• highest quality of info

what are disadvantages of systematic reviews?

• laborious

• time consuming

• difficult to combine info when methods and measures vary across studies

what type of study design is quantitative and formal epidemiological and used to systematically assess previous research studies to derive conclusions about that body of research?

meta-analysis

meta analysis is similar to literature review except…?

it is a statistical combination of results from 2 or more studies

what are the advantages of meta analysis?

• most idea, efficient, highest quality

• can combine with other study designs

• highest statistical power (large sample size)

• can be generalized and summary findings can be extrapolated

what are disadvantages of meta-analysis?

• may not be possible in all systematic reviews

• individual study biases affect results

• variability in methods/approach

• requires advanced statistical methods/software