_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 ...

_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

_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 ... ...

_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

_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 ... ...

_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

_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

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

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

Define Epidemiology

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

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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

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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Clinical epidemiology = application of epidemiology to … … care

Clinical epidemiology = application of epidemiology to individual patient care

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What is prevalence?

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

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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Prevalence = number of people … / number of people …

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

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

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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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

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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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

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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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

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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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 …

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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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 … …

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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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 … …

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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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:

D… risk factors
B… risk factors
…-related risk factors
E… risk factors
G… risk factors

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:

Demographic risk factors
Behavioural risk factors
Health-related risk factors
Environmental risk factors
Genetic risk factors

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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

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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Calculating Prevalence

A or B?

A
So I would use (A+C) / N as this is total number with the disease over total population at risk

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

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

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

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

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

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

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

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

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

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

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

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

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

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

_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

* 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

_Sources of cross-sectional study data_ * **Primary or secondary data** * Primary data = ... data * Secondary data = ... registers, .../.... records, ... data

* Primary or secondary data * Primary data = **survey** data * Secondary data = **mortality** registers, **hospital/medical** records, **census** data

_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 ...

* _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**

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

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

_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 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

_Strengths and Weaknesses of Secondary Data_ * + It is ... * + If anonymous, minimal ethical/governance ... needed * -Limited by what ... already gathered * --Poor ... and missing ...

* + It is **Cheap** * + If anonymous, minimal **ethical/governance approval** needed * -Limited by what **data** already gathered * --Poor **accuracy** and missing **data**

_Strengths and Weaknesses of Primary Data_ * + Gather ... data * -Difficult to achieve ... sample * -More ... *

* + Gather **additional** data * -Difficult to achieve **representative** sample * -More **expensive**

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

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

_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)

* 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)

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

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

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

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

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

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

Prevalence calculation = ... with disease / ... disease

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

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

**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

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

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

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

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