Notesale: Turn your study into money

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EPIDEMIOLOGY OF CANCER

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à For example, exercise intervention for metastatic prostate cancer and see if
there is an effect on the progression of the cancer
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Study base:
• Reference population
• Source of the study population (i
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where the population source is
from)
• Population giving rise to the cases
• Defined before cases appear by a geographical area or some other
entity like a cohort study
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Person-time:
• Estimate of the actual time-at-risk in years, months, or days that all
persons contributed to a study
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For example, this would be the number of people in the study
multiplied by the median number of years of follow-up
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• One, five and ten-year prevalence’s give an idea of how the disease
is progressing
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Incidence:
• Proportion of a population found to have a condition over a
period of time
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• European age-standardised is important because we have an idea
of the geographical life expectancy that influences the incidence of
that disease
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Risk:
• Probability of disease developing in an individual in a specified
time interval
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those who have a low intake of soda
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• RR: 1
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00, 2
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• RR: 2 à twice as likely of developing the outcome than the control



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unexposed
• Absolute: i
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incidence, prevalence

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Absolute allows us to think about how it is affecting the society
when making decisions about drugs
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These are studies that investigate risk factors of health outcomes in which
the unit of analysis are populations or groups rather than individuals
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For example, patterns of cigarette consumption and bladder cancer – plot
over time how cigarette consumption and bladder cancer changes over
the years
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They also allow us to generate hypothesis based on data
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Advantages include:
• Easy to do
• No individual data necessary

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You identify by the case or the control, using questionnaires
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However, a disadvantage would be recall bias, which is a big limitation of
case-control studies
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Another disadvantage would be misclassification of information – a lot of
room for errors
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However, an advantage would be for rare cancers such as pancreatic
cancer, and this would be suitable because you can work backwards
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Other advantages include:
• Time and cost efficient
• Assessment of several exposures


Cohort Studies:
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Disadvantages:
• Expensive
• Not suitable for rare diseases
• Takes a lot of time


Interventions:
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Notes:
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Study population – group of individuals that serve as study participants
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Internal validity – validity of the inferences as they pertain to members
of the source population and is a prerequisite for external validity
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External validity/generalizability – validity of the inferences as they
pertain to people outside that population
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Overall, if a study is valid then it means that it lacks bias
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Bias is the systematic error in the study design that results in an estimate
of the association between exposure and outcome that is different from
the causal association
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Bias can come from the selection of participants or the measurement of
aspects (e
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exposure, outcome, confounders) on the selected
participants
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Selection bias – distortions that result from procedures used to select
subjects and from factors that influence study participation
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• Selection bias is a particular problem in case-control studies
because the selection of cases and controls, which takes place after
the outcome has occurred, may be related to the exposure
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• Self-selection bias/ self-referral is considered a threat to validity
since the reasons for self-referral may be associated with the
outcome
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Types of information bias:
• Differential misclassification – classification error that depends
on the values of other variables
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- Recall bias can occur in case-control studies when cases
recall their past exposures differently than controls
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• Non-differential misclassification – classification error that does
not depend on values of other variables
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Misclassification would
be when the proportion of subjects misclassified on
exposure does not depend on the disease status
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Confounding – may be considered a confusion of effects
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• Increasing trend for prevalence of Down syndrome with increasing
birth order à effect if birth order of the occurrence of Down
syndrome
• Maternal age is more strongly associated with Down syndrome
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- The exposure or the disease must not affect a confounding
factor – it cannot be an intermediate factor
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Is a review that has been prepared using a systematic approach to
minimize bias and random errors
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There is a systematic approach to:
• Define specific research question
• Identification of studies
• Selection of studies
• Data extraction
• Critical appraisal of evidence

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