PUBLIC HEALTH Flashcards
What is sensitivity?
Sensitivity: The ability of a test to correctly identify those with the condition (true positive rate).
TP / (TP + FN )
What is specificity?
Specificity: The ability of a test to correctly identify those without the condition (true negative rate).
Proportion of patients without the condition who have a negative test result
TN / (TN + FP)
What is the positive predictive value?
The chance that the patient has the condition if the diagnostic test is positive
TP / (TP + FP)
What is Negative predictive value?
The chance that the patient does not have the condition if the diagnostic test is negative
TN / (TN + FN)
What is the likelihood ratio for a positive test result?
Likelihood Ratio for a Positive Test (LR+): How much more likely a positive test result is in someone with the condition compared to someone without it.
sensitivity / (1 - specificity)
What is the likelihood ratio for a negative test result?
Likelihood Ratio for a Negative Test (LR-): How much less likely a negative test result is in someone with the condition compared to someone without it.
(1 - sensitivity) / specificity
What is a problem with case control studies?
Recall bias
What is a Cohort study?
Observational and prospective. Two (or more) are selected according to their exposure to a particular agent (e.g. medicine, toxin) and followed up to see how many develop a disease or other outcome.
The usual outcome measure is the relative risk.
Examples include Framingham Heart Study
What is a case-control study?
Look at group of people w a condtion, and compare them to a control group.
Researchers look back to see if there were any differences in exposures or risk factors between the groups. It helps find possible causes of the condition.
The usual outcome measure is the odds ratio.
Inexpensive, produce quick results
Useful for studying rare conditions
Prone to confounding
What is a cross-sectional study?
Provide a ‘snapshot’, sometimes called prevalence studies
Provide weak evidence of cause and effect
What is a type 1 error?
Two types of errors may occur when testing the null hypothesis
type I: the null hypothesis is rejected when it is true
What is a type 2 error?
type II: the null hypothesis is accepted when it is false - i.e. Failing to spot a difference when one really exists, a false negative.
How do you work out relative risk?
Work out the odds in each group.
Then divide the odds of each group together and that gives you the outcome
EER/CER
Relative risk reduction (RRR) or relative risk increase (RRI) is calculated by dividing the absolute risk change by the control event rate
Using the above data, RRI = (EER - CER) / CER = (0.6 - 0.25) / 0.25 = 1.4 = 140%
What is absolute risk reduction?
Absolute risk reduction (ARR) is calculated as the difference in event rates between two groups. In this context, it represents the additional benefit of one treatment over another in reducing pain.
Subtracting the risk of pain in the usual treatment group (1,340 / 1,530) by the risk of pain in the current best treatment group (1,578 / 1,820). 87.6% - 86.7% = 0.9%
How do you work out odds ratio?
odds of contracting the condition in the exposed / odds of contracting the condition in the unexposed.
eg
40 out of 60 smokers have lung cancer
10 out of 90 non smokers have lung cancer
Odds of lung cancer in smokers 40/60
odds of lung cancer in non smokers 10/90
40/60 = 0.66
10/90 =0.11
0.66/0.11= 6
This means smokers are 6 times more likely to have the disease compared to non-smokers.
Interpretation:
OR = 1: No association between exposure and outcome.
OR > 1: Positive association (exposure increases odds of the event).
OR < 1: Negative association (exposure decreases odds of the event).
Different types of plot chart?
Funnel plot: Funnel plots are primarily used to demonstrate publication bias in meta-analyses. As publication bias is being investigated here, and the researcher is conducting a meta-analysis, a funnel plot is the best answer
Box-and-whisker plot: This is a graphical representation of the sample minimum, lower quartile, median, upper quartile and sample maximum. This helps show the distribution of quantitative data. However, it does not demonstrate publication bias.
Forest plot Forest plots are usually found in meta-analyses and provide a graphical representation of the strength of evidence of the constituent trials
Histogram A graphical display of continuous data where the values have been categorised into a number of categories
Scatter plot Graphical representation using Cartesian coordinates to display values for two variables for a set of data
Kaplan-Meier survival plot A plot of the Kaplan-Meier estimate of the survival function showing decreasing survival with time
What is the standard error of the mean?
Standard error of the mean = standard deviation / square root (number of patients)
What are the advantages and disadvantages of a case-control study?
Advantages:
- Good for rare outcomes
- Quicker than cohort or intervention
- Can investigate multiple exposures
Disadvantages:
- Difficulties finding controls of match with cases
- Prone to selection and information bias
What are some advantages and disadvantages of cohort studies?
Advantages:
- Can follow-up group with a rare exposure
- Good for common and multiple outcomes
- Less risk of selection and recall bias
Disadvantages:
- Take a long time
- Loss to follow up
- Need a large sample size
What are some advantages and disadvantages of a cross-sectional study?
Advantages:
- Cheap and quick
- Provide data on prevalence at a single point in time
- Large sample size
- Good for public health planning
Disadvantages:
- Risk of reverse causality (don’t know whether outcome or exposure came first)
- Cannot measure incidence
- Risk of recall bias and non-response
What are the advantages and disadvantages of RCT?
Advantages:
- Low risk of bias and confounding
- Can infer causality
Disadvantages:
- Time consuming
- Expensive
- Specific inclusion/exclusion criteria may mean the study population is different from typical patients
What are the different factors that can explain associations?
- Chance
- Bias
- Confounding
- Reverse causality
- A true association
What is selection bias and what can cause it?
Systematic error in the selection of study participants of the allocation to different study groups
- Non- response
- Loss to follow up
- Are those in the intervention group different to those in the control group
What are the different types of information bias?
Measurement (e.g. different equipment used to measure the outcome in the different groups)
*Observer (e.g. the researcher knows which participants are cases and which are controls and subconsciously reports/measures the exposure or outcome differently depending on which group they are in)
- Recall (e.g. events that happened in the past are not remembered and reported accurately)
- Reporting (e.g. respondents report inaccurate information because they are embarassed)
What is a cross-sectional study?
Provide a ‘snapshot’, sometimes called prevalence studies
Provide weak evidence of cause and effect
Define what numbers needed to treat is
The number of patients who need to receive a treamtment in Order for one person to benefit
worked out as
1/absolute risk reduction
say a drug reduced risk of MI from 10% to 5%
absolute risk reduction would be 0.05 (5%)
1/0.05 = 20
so 20 people would needed to take drug to prevent one person having a heart attack
In the theory of planned behavior what 3 factors influence intentions?
Attitude towards the behavior: this refers to an individual’s positive or negative evaluation of performing the behavior
Subjective norm: this reflects the perceived social pressure to engage or not engage in the behavior. It involves the influence of important others (e.g., family, peers, society) and their expectations or approval of the behavior (e.g., “Do people who matter to me think I should do this?”).
Perceived behavioral control (PBC): This refers to the individual’s perception of their ability to perform the behavior, influenced by both internal factors (e.g., self-confidence, skills) and external factors (e.g., availability of resources, opportunities). It is similar to the concept of self-efficacy. The more control a person believes they have over performing a behavior, the more likely they are to intend to do it.
The TPB model
Attitude: Beliefs about the behavior → Evaluation of outcomes (positive/negative)
Subjective Norm: Normative beliefs (perceptions of others’ expectations) → Motivation to comply
Perceived Behavioral Control: Control beliefs (resources, opportunities) → Confidence in ability to perform the behavior
Intention: The likelihood of engaging in the behavior
Behavior: The actual action or decision
ASP
What are the strengths and weaknesses of the TPB?
Strengths:
It provides a comprehensive framework that includes both individual (attitude, perceived control) and social (subjective norm) factors.
It has been empirically supported in many domains, especially health psychology and consumer behavior.
Limitations:
TPB assumes that people are rational decision-makers, which doesn’t always align with real-world, emotional, or impulsive behaviors.
It can be hard to measure some of the constructs, especially perceived behavioral control, which is often subjective.
The model primarily focuses on individual-level factors and might not fully account for systemic or structural barriers.
What are the 3 ways to perform a health needs assessment?
What is a health needs assessment?
A Health Needs Assessment (HNA) identifies the health needs of a population to prioritize and allocate resources effectively. It evaluates gaps in services and helps plan interventions to improve public health.
- epidemiological
- Corporate
- Comparative
What is the epidemiological approach to a health needs assessment?
Epidemiological Approach:
Focuses on data and statistics.
Analyzes the prevalence, incidence, and distribution of diseases.
Uses evidence from studies to identify health problems.
What are some pros and cons to an epidemiolocal approach to a health needs assessment?
Advantages:
- Uses existing data
- Provides data on disease
- Incidence
- Can evaluate services by trends over time
Disadvantages:
- Quality of data variable
- Data collected may not be the data required
- Does not consider the felt needs or
opinions/experiences of the people affected
What is the corporate approach to a health needs assessment?
- Ask the population what their needs are
- Use focus groups meetings etc
- Engages stakeholders (e.g., community groups, healthcare providers).
What are the advantages and disadvantages to the corporate approach?
Advantages:
- Based on the felt and expressed needs of the population in question
- Recognises the knowledge of those in the population
- Takes into account a wide range of views
Disadvantages:
- Difficult to distinguish need from demand
- Groups may have vested interest
- May be influenced by political agendas
What is the comparative approach to a health needs assessment?
Compares services or health outcomes across populations (e.g., regions or countries).
Highlights inequalities and areas needing improvement.
Identifies “best practices” for replication.
What are the Adv vs Dis for comparative approach?
Adv:
- Quick and cheap
- Gives a measure of relative performance
Dis:
- May be difficult to find comparable population
- Data may not be available/high quality
- May not yield what the most appropriate level
(e.g. of provision or utilisation) should be
What are Bradshaw’s 4 types of health need?
Bradshaw’s 4 Types of Health Needs provide a framework to understand different perspectives on health needs:
Normative Need:
Felt Need:
Expressed Need:
Comparative Need:
Summary:
Bradshaw’s framework distinguishes between needs defined by experts, individuals, and comparisons to ensure a comprehensive approach to addressing health needs.
Bradshaws types of health need - define and give example of normative and felt need
Normative Need:
Defined by professionals or experts based on standards or guidelines.
Example: A doctor recommends vaccinations to reduce disease risk.
Felt Need:
What individuals feel they need, based on personal experiences.
Example: A person reports feeling anxious and seeks mental health support.
Bradshaws types of health need - define and give example of Expressed need and comparative need
Expressed Need:
A felt need that has been acted upon or expressed as a demand.
Example: Long waiting lists for physiotherapy reflect expressed demand for the service.
Comparative Need:
Identified by comparing one group to another with similar characteristics.
Example: One area has fewer healthcare facilities than a neighboring area with the same population size.