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3A > Stats and ethics > Flashcards

Stats and ethics Flashcards

1
Q

What is sensitivity?

A

Proportion of patients with the condition who have a positive test result

TP / (TP + FN )

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2
Q

What is specificity?

A

Proportion of patients without the condition who have a negative test result

TN / (TN + FP)

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3
Q

What is the positive predictive value?

A

The chance that the patient has the condition if the diagnostic test is positive

TP / (TP + FP)

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4
Q

What is Negative predictive value?

A

The chance that the patient does not have the condition if the diagnostic test is negative

TN / (TN + FN)

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5
Q

What is the likelihood ratio for a positive test result?

A

How much the odds of the disease increase when a test is positive

sensitivity / (1 - specificity)

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6
Q

What is the likelihood ratio for a negative test result?

A

How much the odds of the disease decrease when a test is negative

(1 - sensitivity) / specificity

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7
Q

What is a problem with case control studies?

A

Recall bias

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8
Q

What is a Cohort study?

A

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

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9
Q

What are some advantages and disadvantages of cohort studies?

A

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

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10
Q

What is a case-control study?

A

Observational and retrospective. Patients with a particular condition (cases) are identified and matched with controls. Data is then collected on past exposure to a possible causal agent for the condition.

The usual outcome measure is the odds ratio.

Inexpensive, produce quick results
Useful for studying rare conditions
Prone to confounding

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11
Q

What are the advantages and disadvantages of a case-control study?

A

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

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12
Q

What is a cross-sectional study?

A

Provide a ‘snapshot’, sometimes called prevalence studies

Provide weak evidence of cause and effect

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13
Q

What are some advantages and disadvantages of a cross-sectional study?

A

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

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14
Q

What are the advantages and disadvantages of RCT?

A

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

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15
Q

What are the different factors that can explain associations?

A
  • Chance
  • Bias
  • Confounding
  • Reverse causality
  • A true association
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16
Q

What is selection bias and what can cause it?

A

Systematic error in the selection of study participants of the allocation to different study groups

  1. Non- response
  2. Loss to follow up
  3. Are those in the intervention group different to those in the control group
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17
Q

What are the different types of information bias?

A

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)
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18
Q

What is a type 1 error?

A

Two types of errors may occur when testing the null hypothesis
type I: the null hypothesis is rejected when it is true

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19
Q

What is a type 2 error?

A

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.

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20
Q

How do you work out relative risk?

A

Relative risk (RR) is the ratio of risk in the experimental group (experimental event rate, EER) to risk in the control group (control event rate, CER).

The term relative risk ratio is sometimes used instead of relative risk.

EER/CER

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21
Q

What is absolute risk reduction?

A

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%

22
Q

How do you work out odds ratio?

A

Work out the odds in each group.

Then divide the odds of each group together and that gives you the outcome

23
Q

Different types of plot chart?

A

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

24
Q

What is the standard error of the mean?

A

Standard error of the mean = standard deviation / square root (number of patients)

25
Q

What is a cross-sectional study?

A

Provide a ‘snapshot’, sometimes called prevalence studies

Provide weak evidence of cause and effect

26
Q

NNT?

A

Number Needed to Treat (NNT) is a metric used to determine how many patients need to be treated in order to prevent one additional adverse outcome. It is derived by taking the reciprocal of the absolute risk reduction (ARR), which can be calculated using the formula: 1 / ARR. The ARR itself is found by subtracting the control event rate (CER) from the experimental event rate (EER). In this instance, NNT equals 1 / (EER - CER) = 1 / ((45/89) - (12/102)) = 2.58.

1/ ARR

27
Q

In the theory of planned behavior what 3 factors influence intentions?

A

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.

28
Q

The TPB model

A

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

29
Q

What are the strengths and weaknesses of the TPB?

A

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.

30
Q

What are the 3 ways to perform a health needs assessment?

A
  1. epidemiological
  2. Corporate
  3. Comparative
31
Q

What is the epidemiological approach to a health needs assessment?

A
  • Disease incidence and prevalence
  • Morbidity and mortality
  • Life expectancy
  • Services avaliable
32
Q

What are the advantages and disadvantages of the epidemiological approach to the health needs assessment?

A

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

33
Q

What is the corporate approach to a health needs assessment?

A
  • Ask the population what their needs are
  • Use focus groups meetings etc
  • Wide variety of stakeholders
34
Q

What are the advantages and disadvantages to the corporate approach?

A

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

35
Q

What is the comparative approach to a health needs assessment?

A

Compare the health or healthcare provision of one population to another
* Spatial (e.g. different towns) or social (e.g. age, social class)
* Can compare health, service provision/utilisation, health outcomes
*Means of evaluating variation in performance/costs of services

36
Q

What are the Adv vs Dis for comparative approach?

A

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

37
Q

What are the key components of Beckers health belief model?

A

Perceived Susceptibility

Perceived Severity

Perceived Benefits

Perceived Barriers

Cue to action

Self-Efficacy

Social and Environmental Factors

38
Q

What are the 4 main beliefs of the health belief model?

A

Belief they are susceptible to the condition, Belief in serious consequences,
Belief that taking action reduces susceptibility, Belief that the benefits of action outweigh the costs

39
Q

What is Perceived Susceptibility?

A

An individual’s belief about the likelihood of getting a disease or condition. For example, someone who believes they are at high risk of developing diabetes is more likely to take preventive measures (such as dieting or exercising).

40
Q

What is perceived severity?

A

An individual’s belief about the seriousness of a health issue and its consequences. If someone believes that a condition like lung cancer will have severe consequences, they may be more motivated to stop smoking.

41
Q

What is perceived benefits?

A

The belief that taking a specific action will reduce the threat of a health problem. For instance, if an individual believes that wearing a seatbelt significantly reduces the risk of injury in a car accident, they are more likely to wear one.

42
Q

What is perceived barriers?

A

The perceived obstacles or costs associated with taking the recommended health action. Even if an individual believes that exercise will improve their health, they may avoid it due to perceived barriers like lack of time or energy.

43
Q

What is Cue to action?

A

A trigger that motivates a person to take action. This could be an internal cue, such as feeling unwell, or an external cue, such as a health campaign or a doctor’s recommendation.

44
Q

What is self-efficacy?

A

Added later by Becker and others, this refers to the belief in one’s ability to successfully carry out the recommended health behavior. The higher one’s self-efficacy, the more likely they are to take action. This concept emphasizes confidence in personal ability to make health changes.

45
Q

What are the 3 applications of becker’s model?

A

Health promotion campaigns: It can be used to design interventions that target specific beliefs (e.g., promoting awareness about the risks of smoking).

Chronic illness management: For people managing long-term conditions, understanding perceived barriers and benefits (e.g., taking medication regularly) can help improve adherence.

Public health initiatives: The model is used to tailor messages about vaccines, screenings, or health behaviors by addressing individuals’ concerns and motivations.

46
Q

What are the 10 criteria in Wilson and Jugner screening criteria?

A
  • Should be an important health problem
  • Should be an accepted treatment
  • Facilities and treatment should be available
  • Should be a recognizable latent or early symptomatic stage.
  • Suitable test or examination
    -Test should be acceptable to the population
  • Natural history of the condition, including the development from latent to declared disease, should be understood
  • Should be an agreed policy on whom to treat.
  • Costs of the screening program (including diagnosis and treatment) should be balanced against the benefits.
  • Case-finding should be a continuing process
47
Q

What are the factors for causality in the Bradford-hill criteria?

A
  • Strength
  • Consistency: same result from various studies
  • Dose-response
  • Temporality: Exposure occurs prior to outcome
  • Plausibility: Reasonable biological mechanism
  • Reversibility: Intervention to reduce/remove exposure eliminates/reduces outcome
  • Analogy: Similarity with other established cause-effect relationships
  • Specificity: Relationship specific to outcome of interest
48
Q

What is length time bias?

A
  • studies when the detection of a disease or condition is more likely to occur in individuals with a slower progression of the disease, leading to an overestimation of survival rates or the effectiveness of a treatment
49
Q

What is lead time bias?

A

detecting the presence of disease earlier, screening can appear to increase length of
survival even if it has no impact on the course of the disease.

50
Q

What are the stages of the transtheoretical model?

A

Pre-contemplation
Contemplation
Preparation
Relapse
Maintenance
Action

3A (11 decks)

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