Flashcards in Week 122 - Measurements in population I Deck (36):
What is incidence?
Proportion of a group that will develop a certain disease over a time period
What is prevalence?
Amount/proportion of people that have a disease at a given time
List the study order of hierachy of evidence?
1) Systematic reviews with at least one RCT
3) Non RCTs
4) Cohort studies
5) Case-control studies
6) Self controlled case series
7) Ecological studies
8) Cross sectional studies of incidence and prevalence
9) Case series and case reports
What is an RCT?
A randomised controlled trial
Randomisation of sorting people into groups removes any confounding factors between the intervention group and control group
What is a self controlled case series?
A study in which the incidence of a certain outcome is compared to the incidence of the outcome when the individual is not exposed
e.g. occurence of adverse reaction when given a drug compared to when not given
What is a cross sectional study?
A study that collects data on incidence/prevalence of a disease in a population at a specific point in time
What is an ecological study?
A study in which populations/groups are analysed to study effects of risk factor on health
e.g. rates of obesity in different countries
What is the disadvantage of an ecological study?
Hard to control due to confounding variables
What is a case report study?
A detailed report of a patient with a condition of interest
What is a case series study?
A descriptive study of patients with a known exposure or condition
What is a disadvantage of case-series study?
Can involve selection bias
List the two types of research studies?
What is an experimental study?
Study which exposure is determined as part of study design
What is an observational study?
Study in which exposure is not determined as part of the study design
- already existing expossure and consequences are studied
Give an example of an experimental study?
What is the null hypothesis?
Statement being tested in a test of hypothesis
What is the alternative hypothesis?
What is believed to be true if the null hypothesis is false
What is a case control study?
A study which starts with the identification of people:
- with the disease of interest, and a
- control group without the disease
What is a retrospective case control study?
A case control study which starts with the case and looks back at exposure to see if there is an associated risk
What is a prospective case control study?
A case control study which recruit individuals as they develop the disease of interest
What is a p-value?
Probability of observing a difference as large as previously seen in a study due to chance
p-value < 0.05 => statistically significant
What is a cohort study?
A study that starts by looking at a certain group of people and identifies those who are exposed to the risk factors and those who are not.
It then compares the incidence of disease development between the two exposure groups.
What is the difference between a prospective and retrospective cohort study?
Prospective = current exposure
Retrospective = identifies "past" exposure to risk factors
What are the advantages of a case control study?
Better for rare diseases
Retrospective case controls are quick and cheap
What are the disadvantages of a case control study?
Prone to bias
Time of first exposure to risk factor is difficult to judge
Incidence can't be determined
What are the advantages of a cohort study?
Better for rare exposures
View the multiple effects of one exposure
Less prone to bias
Incidence can be determined
What are the disadvantages of a cohort study?
Can be slow and expensive
What are the two types of random errors?
Type 1 = alpha error
Type 2 = beta error
What is a type 1 error?
A false positive
What is a type 2 error?
A false negative
How can type 1 errors be controlled?
By lowering the statistical significance level
How can type 2 errors be controlled?
Increase sample size and power of the study
What is sensitivity?
Measurement of how good a test is at diagnosing disease?
i.e. true positive rate
A high sensitivity reduced type 2 error
What is specificity?
Measurement of how good a test is at diagnosing no disease?
i.e. true negative rate
High specificity reduces type 1 errors
What is the formula for relative risk?
(Absolute risk when exposed) / (absolute risk when non-exposed)
i.e. [De / (De + He)] / [De' / (De' + He')]