WK 2- EPIDEMIOLOGY Flashcards
What is prevalence
Indicates how widespread a disease is at a point in time by comparing the number of people who have the condition with the number of people who don’t
What is incidence
Conveys information about risk of contracting the disease
What is absolute risk and what is the formula to calculate it
Absolute risk is the probability that a specified event will occur in a specified population
Calculated by: number of events in a specified group/number of people in that group
What is attributable risk and how is it calculated
Amount of risk that can be attributed to an exposure- calculated from the difference in absolute risk for exposed and unexposed individual (ARE-ARC)
What is relative risk and how is it calculated
Ratio of the risk of disease among those exposed to a risk factor compared to risk of those not exposed (ARE/ARC) (ARE= risk of exposed, ARC=risk of not exposed)
What is the odds ratio and how is it calculated
Ratio of two odds giving an approximate value for the risks of the exposure examined in that study
OR= odds of being exposed in those with disease/odds of being exposed in those without the disease
(ad/bc)-> eg. exposure to smoking is associate with 1.97 times the risk of lung cancer compared to not smoking
What is sensitivity and how is it calculated
Probability of a positive test among patients with the disease
-> correct positive (number of people who tested positive for disease and actually had disease)/number of positive with disease (CP+FN)
What is specificity and how is it calculated
Probability of a negative test among patients with the disease
–> correct negative (no. of people who tested negative and are negative)/total negative with disease (FP+CN)
What is a positive predictive value (PPV)
Probability that a disease is present given that a diagnostic test is positive
= correct positive/ (correct positive + false positive)
What is a negative predictive value (NPV)
Probability that a disease is not present given that a diagnostic test is negative
= correct negative/ (correct negative+ false negative)
–> CN+FN= total number of negative tests
What is the relationship between prevalence and predictive values
Predictive values depend strongly on the prevalence of the disease
-Decreasing prevalence will case the PPV to decrease and the NPV to increase
What is the numbers needed to treat and how is it calculated
NNT is the number of people who need to take a specific treatment in order for one person to benefit
NNT= 1/Absolute risk reduction
What is Absolute risk reduction (ARR)
Absolute risk of control-absolute risk of the treatment group
-> ARR (for beneficial treatments) is identical to Attributable Risk (for risky exposures) –it is the context that changes
What is numbers needed to harm and how is it calculated
NNH is how many patients need to be exposed to a risk factor over a specific period to cause harm to 1 patient that would otherwise not be harmed
NNH= 1/AR (absolute risk)
What are some modifiable factors that are used in the primary prevention of cancer
- diet (processed meat has a high attributable risk to colon cancer)
- tobacco (has a high attributable risk to lung cancer)
- alcohol- risk increases with increasing consumption
- lack of physical activity (obesity is linked to numerous cancers)
- infections (eg HPV and cervical cancer)
- environmental exposure (high UV is linked to skin cancer)
What is primary prevention, secondary prevention and tertiary prevention?
- primary= preventing the disease from occurring
- secondary= aims to stop or slow the progression of a disease- early identification and treatment
- tertiary= preventing relapse/worsening of the disease, monitoring
What is the national screening approach for breast cancer
Screening is for women of normal risk from age 50-75, mammogram every 2 years
-those at higher risk: recommend breast awareness and start individual monitoring strategies
What is the national screening approach for prostate cancer
Routine screening for prostate cancer with digital rectal examination, PSA or transabdominal ultrasound is not recommended as it is insufficiently sensitive to detect prostate cancers early enough
-You can offer a PSA is the patient still wishes to be tested after being given all relevant information about possible harms (false positives and false negatives that may come from a low sensitivity test)
What is the national screening approach for cervical cancer
Women of any age who have symptoms (including pain or bleeding) should have appropriate clinical assessment, which may include a cervical cytology test and an HPV test. Women between 70 and 74 years of age who have had a regular screening test will be recommended to have an exit HPV test before leaving the cervical screening program
What is the national screening approach for bowel cancer
Screening program is for people with normal to slightly above normal risk, perform FOB (fecal occult blood) test every 2 years from age of 50 until 75 years of age with repeated negative findings
What is a cross sectional study
Measures the prevalence of exposure and disease at the same time
What is a case control study
Begins with people with a disease (cases) and compares them to people without a disease (control), always retrospective
What is a cohort study
Compares the rate of disease in a group of people exposed to a factor with a group of people who aren’t exposed, aim is to identify associations between risk factors and the outcome, usually prospective
What are randomised control trials
Prospective cohort study where conditions are specified by the investigator and involved at least two groups and involves an intervention- individuals are followed to ascertain effects of the intervention
What is a confounding factor
A variable in a quantitative research study that explains some or all of the correlation between the dependent variable and an independent variable
What is an example of a confounding factor
Eg. if you are researching whether lack of exercise leads to weight gain, lack of exercise is your independent variable and weight gain is your dependent variable. Confounding variables are any other variable that also has an effect on your dependent variable, such as genetics, metabolic disorders.
