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Year 2 Medicine > Thinking about Populations at a moment in time: Prevalence and Cross-Sectional studies: Infertility > Flashcards

Thinking about Populations at a moment in time: Prevalence and Cross-Sectional studies: Infertility Flashcards

1
Q

Define Epidemiology

A

basic science of the distribution and determinants of the frequency of disease/ health outcomes in specified populations

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2
Q

Relevance of describing populations and health needs

  • … facilitates … and … of health problems – and evaluation of …
  • … methods = techniques used to derive … knowledge
  • Clinical … = application of … to individual … care
A
  • Epidemiology facilitates prevention and management of health problems – and evaluation of interventions
  • Research methods = techniques used to derive epidemiological knowledge
  • Clinical epidemiology = application of epidemiology to individual patient care
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3
Q

Clinical epidemiology = application of epidemiology to … … care

A

Clinical epidemiology = application of epidemiology to individual patient care

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4
Q

What is prevalence?

A

Prevalence measures the frequency of “cases” of a disease in a given population at a designated time (the numerator). E.g. diagnosed asthma in children aged 5-11 years.

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5
Q

Calculation of prevalence also requires a suitable … (e.g. GP registered patients, schoolchildren) – the number of people who are ‘at …’ of the disease

A

Calculation of prevalence also requires a suitable denominator (e.g. GP registered patients, schoolchildren) – the number of people who are ‘at risk’ of the disease

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6
Q

Prevalence = number of people … / number of people …

A

number of people with disease / number of people who could have disease.

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7
Q

Prevalence is expressed as a … (e.g. …), a … of 1 (0.7 is equivalent), or a proportion per … of … (E.g. … of … )

A

Prevalence is expressed as a percentage (e.g. 70%), a proportion of 1 (0.7 is equivalent), or a proportion per unit of population (700 of every 1000 people)

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8
Q

Types of Prevalence: Point

  • This is either A or B

A) Prevalence calculated for a specific purpose

B) Prevalence at a point in time

Give an example

A
  • This is:

A) Prevalence calculated for a specific purpose

B) Prevalence at a point in time

Example: No of women experiencing infertility right now

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9
Q

Types of Prevalence: Period

  • This is either A or B

A) Prevalence over a specific period of time

B) Prevalence of an episodic disease/condition

Give an example

A
  • This is either A or B

A) Prevalence over a specific period of time

B) Prevalence of an episodic disease/condition

Example: Women who have experienced infertility in past 12 months

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10
Q

Types of Prevalence: Lifetime

  • This is either A or B

A) Prevalence within period of time over which disease typically lasts

B) Prevalence of the disease/condition ever in individual’s lifetime

Give an example

A
  • This is either A or B

A) Prevalence within period of time over which disease typically lasts

B) Prevalence of the disease/condition ever in individual’s lifetime

Example: Women who have experienced infertility ever in their lifetime

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11
Q

Advantages and Disadvantages of Point Prevalence

Advantages Include:

  • Identify … in disease/condition frequency and/or intervention …
  • If based on survey data, robust to patient … problems

Disadvantages Include:

  • Less helpful for diseases/conditions which are …, … in duration or which …
A

Advantages Include:

  • Identify changes in disease/condition frequency and/or intervention effectiveness
  • If based on survey data, robust to patient recall problems

Disadvantages Include:

  • Less helpful for diseases/conditions which are rare, short in duration or which fluctuate
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12
Q

Advantages and Disadvantages of Period Prevalence

Advantages Include:

  • Helpful for diseases/ conditions which … e.g. …
  • Helpful in identifying … in disease/ condition frequency and/ or intervention …

Disadvantages Include:

  • If based on survey data, problems with … …
A

Advantages Include:

  • Helpful for diseases/ conditions which fluctuate e.g. hay fever
  • Helpful in identifying changes in disease/ condition frequency and/ or intervention effectiveness

Disadvantages Include:

  • If based on survey data, problems with participant recall
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13
Q

Advantages and Disadvantages of Lifetime Prevalence

Advantages Include:

  • Helpful for diseases/ conditions which are … e.g. …

Disadvantages Include:

  • Less helpful for knowing how many people … affected by diseases/conditions which are …-limited
  • Less helpful in identifying … in disease/condition frequency and/or intervention …
  • If based on survey data, problems with … …
A

Advantages Include:

  • Helpful for diseases/ conditions which are episodic e.g. puerperal psychosis

Disadvantages Include:

  • Less helpful for knowing how many people currently affected by diseases/conditions which are time-limited
  • Less helpful in identifying changes in disease/condition frequency and/or intervention effectiveness
  • If based on survey data, problems with participant recall
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14
Q

Exposures - Risk Factors

  • Attributes that … or … the … of developing a disease or injury
  • May be … - decrease likelihood
  • Types of risk factors that might be considered:
  1. D… risk factors
  2. B… risk factors
  3. …-related risk factors
  4. E… risk factors
  5. G… risk factors
A
  • Attributes that increase or decrease the likelihood of developing a disease or injury
  • May be protective - decrease likelihood
  • Types of risk factors that might be considered:
  1. Demographic risk factors
  2. Behavioural risk factors
  3. Health-related risk factors
  4. Environmental risk factors
  5. Genetic risk factors
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15
Q

Calculating Prevalence

  • We can just calculate basic prevalence within a population
  • But we might also want to know about how prevalence is impacted by an …
  • So an … here being something that is a … … for prevalence or a cause
  • So we have simple prevalence here – so we would add A and C together, this reflects … with the disease
  • And then we would divide that by N which is everyone i.e. the whole … at …
  • And then if you wanted to, you could separate disease prevalence into numbers of people with a disease who have and have not been … to any particular … factor and compare them
A
  • We can just calculate basic prevalence within a population
  • But we might also want to know about how prevalence is impacted by an exposure
  • So an exposure here being something that is a risk factor for prevalence or a cause
  • So we have simple prevalence here – so we would add A and C together, this reflects everyone with the disease
  • And then we would divide that by N which is everyone i.e. the whole population at risk
  • And then if you wanted to, you could separate disease prevalence into numbers of people with a disease who have and have not been exposed to any particular risk factor and compare them
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16
Q
A
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17
Q

Calculating Prevalence

  • A or B?
A
  • A
  • So I would use (A+C) / N as this is total number with the disease over total population at risk
18
Q

Case definition = criteria for identifying … (case) of …/…

A

Case definition = criteria for identifying presence (case) of disease/outcome

19
Q

Defining and operationalising: Case definition (the numerator)

  • Case definition = criteria for identifying presence (case) of … / …
    • The definition of ‘…’ is crucial – and can be very complex
  • Must be clearly defined and specified:
    • … within a study
    • … to other studies
    • r…
    • leading to … and … results
A
  • Case definition = criteria for identifying presence (case) of disease/outcome
    • The definition of ‘caseness’ is crucial – and can be very complex
  • Must be clearly defined and specified:
    • consistent within a study
    • comparable to other studies
    • reproducible
    • leading to interpretable and meaningful results
20
Q

Defining and operationalising: Specified population (the denominator)

  • We must then also define the denominator – this can be very complex too
  • We need to identify those people truly … to the …/…
  • i.e. … people who can’t get it
  • And specify further … details e.g. who, where, when
A
  • We must then also define the denominator – this can be very complex too
  • We need to identify those people truly susceptible to the disease/condition
  • i.e. excluding people who can’t get it
  • And specify further population details e.g. who, where, when
21
Q

Why might we be interested in prevalence of infertility?

  • Understanding infertility and its … and …
    • Accurate knowledge of …, … differences -> fertility/reproductive care providers, researchers/policy makers
  • Implications for
    • …- health, happiness
    • … – current and future economy, labour workforce
  • Informing prevention and public health interventions
  • Identifying and prescribing targeted and indicated …
    • What, when, how, who
  • Service planning and …
  • Evaluating … of interventions
  • Comparing … before and after/ with and without interventions
A
  • Understanding infertility and its causes and outcomes
    • Accurate knowledge of trends, geographical differences -> fertility/reproductive care providers, researchers/policy makers
  • Implications for
    • Individuals- health, happiness
    • Society – current and future economy, labour workforce
  • Informing prevention and public health interventions
  • Identifying and prescribing targeted and indicated interventions
    • What, when, how, who
  • Service planning and commissioning
  • Evaluating effectiveness of interventions
  • Comparing prevalence before and after/ with and without interventions
22
Q

Defining and operationalising infertility: The numerator

  • … perception = a sexually-active non-contracepting female without children / lifetime childlessness
  • … perspective = a disease of the reproductive system defined by a failure to achieve clinical pregnancy after 12 months of regular sexual intercourse minus contraception
    • after 6 months when female aged 35 years or more
  • Consider
    • Conception/ Pregnancy / Live birth
A
  • Public perception = a sexually-active non-contracepting female without children / lifetime childlessness
  • Epidemiology = a disease of the reproductive system defined by a failure to achieve clinical pregnancy after 12 months of regular sexual intercourse minus contraception
    • after 6 months when female aged 35 years or more
  • Consider
    • Conception/ Pregnancy / Live birth
23
Q

Defining and operationalising infertility: The denominator

  • Consider
    • Sexual activity without … / Regular sexual activity without … / Sexual activity with unsuccessful contraception / … to achieve pregnancy / … to pregnancy
    • Females or males / Non-heterosexual couples + Non-couples / People engaging in fertility treatment
    • … range
A
  • Consider
    • Sexual activity without contraception / Regular sexual activity without contraception / Sexual activity with unsuccessful contraception / Trying to achieve pregnancy / Time to pregnancy
    • Females or males / Non-heterosexual couples + Non-couples / People engaging in fertility treatment
    • Age range
24
Q

The way in which we define our numerator and denominator matters because:

  • Affects … estimates (fertility estimate ranges e.g. Gurunath et al., 2011; 6.8 – 38.6%)
    • … positives and negatives
    • Increased/decreased numerator
    • Increased/decreased denominator
  • Affects … of findings
    • Exclude sub-populations of interest from numerator/denominator e.g. non-heterosexual /non-couples
  • Affects identification of … factors and outcomes
    • Obscure identification/ascertaining impact of exposures
    • Obscure identification of temporal or geographical trends
  • Affects … planning and …
    • Unable to meet demand/wasted resources
    • Inappropriate targeting of …
  • Affects …
    • Under or over-investigation/over-treatment of individuals
A
  • Affects prevalence estimates (fertility estimate ranges e.g. Gurunath et al., 2011; 6.8 – 38.6%)
    • False positives and negatives
    • Increased/decreased numerator
    • Increased/decreased denominator
  • Affects coverage of findings
    • Exclude sub-populations of interest from numerator/denominator e.g. non-heterosexual /non-couples
  • Affects identification of causal factors and outcomes
    • Obscure identification/ascertaining impact of exposures
    • Obscure identification of temporal or geographical trends
  • Affects service planning and commissioning
    • Unable to meet demand/wasted resources
    • Inappropriate targeting of resources
  • Affects treatment
    • Under or over-investigation/over-treatment of individuals
25
Q

How do we find the data we need to establish prevalence?

  • We use a … study = identifies e../o.. within people
    • An observational study
    • A defined … is surveyed to simultaneously measure
      • …/ condition status (e.g. infertility)
      • … (e.g. sedentary lifestyle, alcohol intake)
    • Sample selected using inclusion and exclusion criteria
    • Could be general population or clinic-based
    • Prevalence is reported for the population as a whole, and often for subgroups
A
  • We use a cross-sectional study = exposures/outcomes within people
    • An observational study
    • A defined population is surveyed to simultaneously measure
      • Disease/ condition status (e.g. infertility)
      • Exposure (e.g. sedentary lifestyle, alcohol intake)
    • Sample selected using inclusion and exclusion criteria
    • Could be general population or clinic-based
    • Prevalence is reported for the population as a whole, and often for subgroups
26
Q

Sources of cross-sectional study data

  • Primary or secondary data
    • Primary data = … data
    • Secondary data = … registers, …/…. records, … data
A
  • Primary or secondary data
    • Primary data = survey data
    • Secondary data = mortality registers, hospital/medical records, census data
27
Q

Strengths and Weaknesses of Cross-Sectional Studies

  • Strengths:__​
    • Measure … and thus … burden in whole population and subpopulations
    • Can compare prevalence in … and ..-… to risk factors
    • Quick and …
    • Can be used to inform …
    • Can be used to initially … a hypothesis, prior to another type of study
  • Weaknesses:
    • Not suitable for … diseases
    • Not suitable for diseases of … duration
    • Cannot measure rate of … cases arising and any … thereof
    • Vulnerable to …, including …
A
  • Strengths:__​
    • Measure prevalence and thus disease burden in whole population and subpopulations
    • Can compare prevalence in exposed and non-exposed to risk factors
    • Quick and inexpensive
    • Can be used to inform hypotheses
    • Can be used to initially explore a hypothesis, prior to another type of study
  • Weaknesses:
    • Not suitable for rare diseases
    • Not suitable for diseases of short duration
    • Cannot measure rate of new cases arising and any changes thereof
    • Vulnerable to bias, including confounding
28
Q

A … is a variable that influences both the dependent variable and independent variable causing a spurious association.

A

A confounder is a variable that influences both the dependent variable and independent variable causing a spurious association.

29
Q

Cross-sectional studies - the problem of confounding

  • A confounder is a … that influences both the dependent variable and independent variable causing a spurious ….
  • Cross-sectional studies do not provide any protection against confounding because
    • … and … are measured at the same time
    • exposure status is … occurring and not random/manipulated
A
  • A confounder is a variable that influences both the dependent variable and independent variable causing a spurious association.
  • Cross-sectional studies do not provide any protection against confounding because
    • exposures and outcomes are measured at the same time
    • exposure status is naturally occurring and not random/manipulated
30
Q

Strengths and Weaknesses of Secondary Data

    • It is …
    • If anonymous, minimal ethical/governance … needed
  • -Limited by what … already gathered
  • –Poor … and missing …
A
    • It is Cheap
    • If anonymous, minimal ethical/governance approval needed
  • -Limited by what data already gathered
  • –Poor accuracy and missing data
31
Q

Strengths and Weaknesses of Primary Data

    • Gather … data
  • -Difficult to achieve … sample
  • -More …
    *
A
    • Gather additional data
  • -Difficult to achieve representative sample
  • -More expensive
32
Q

Majority of studies on infertility appear to be … (Direkvand-Moghadam A, et al. 2014)

A

Majority of studies on infertility appear to be cross-sectional (Direkvand-Moghadam A, et al. 2014)

33
Q

How do we find the data we need to establish prevalence? (other option)

  • An … study = exposures/outcomes within populations
    • Data collected at the community/population (not …) level
      • Data often existing … e.g. government figures
    • Can be used to …
      • Disease/outcome
      • Exposures
    • Exposures are those relating to the … (not individuals) e.g.
      • Comparing between … area (exposure = area)
      • Comparing across … (exposure = time)
A
  • An ecological study = exposures/outcomes within populations
    • Data collected at the community/population (not individual) level
      • Data often existing standard e.g. government figures
    • Can be used to quantify
      • Disease/outcome
      • Exposures
    • Exposures are those relating to the population (not individuals) e.g.
      • Comparing between geographic area (exposure = area)
      • Comparing across time (exposure = time)
34
Q

… is a basic science focused on understanding disease/health needs of populations

A

Epidemiology is a basic science focused on understanding disease/health needs of populations

35
Q

… is a way of quantifying health needs of populations at a moment in time

A

Prevalence is a way of quantifying health needs of populations at a moment in time

36
Q

… = number of people with disease/condition in a given population at a given time

A

Prevalence = number of people with disease/condition in a given population at a given time

37
Q

Prevalence calculation = … with disease / … disease

A

Prevalence calculation = number of people with disease / number of people who could have disease

38
Q

… studies can be used to capture a ‘snap shot’ of prevalence (of exposures/outcomes) within a population (/subpopulations) at a moment in time

A

Cross-sectional studies can be used to capture a ‘snap shot’ of prevalence (of exposures/outcomes) within a population (/subpopulations) at a moment in time

39
Q

Ecological studies are very similar (to cross-sectional studies), but collect data on … not …

A

Ecological studies are very similar, but collect data on populations not individuals

40
Q
A
41
Q

Cross-sectional studies cannot demonstrate cause and effect and are vulnerable to …

A

Cross-sectional studies cannot demonstrate cause and effect and are vulnerable to confounding

Year 2 Medicine (162 decks)

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