HaDPop Flashcards by Schnell D'Sa

Use of a census

Population
Health
Housing
Employment
Transport
Ethnic group

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Define census

The simultaneous cording of demographic data buy the government at a particular time pertaining to all the persons who live in a particular territory

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Measures of fertility

Crude birth rate
General fertility rate
Total period fertility rate

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Define CBR

Crude birth rate

Number of live births per 1000 population

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Define GFR

General fertility rate

Number of live births per 1000 females aged 15-44 years

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Define TPFR

Total period fertility rate

The average number of children that would be born to a hypothetical woman in her life

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Why use CBR?

Describes impact of births (-deaths +/- migration) on size of population
Takes men into account

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Why use GFR?

Compares fertility of fertile female populations

Requires all women to be known

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Why use TPFR?

Removes influence of age group structure when comparing fertility of fertile females
Removes confounding of age
Only observed in short term study, useless in long

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Define fecundity

Physical ability to reproduce

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Define fertility

Realisation of this potential as births

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What affects fecundity?

Hysterectomy

Sterilisation

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What affects fertility?

Contraception
Abortion
Good economic climate
Increased sexual activity

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Measures of mortality

Crude death rate
Age specific death rate
Standardise mortality rate

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Define CDR

Crude death rate

Number of deaths per 1000 population

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Define ASDR

Age-specific death rate

Number of deaths per 1000 in age group

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Define SMR

Standardised mortality ratio
Compared ‘observed’ number of deaths with number ‘expected’ (reference group)
Adjusted for age-sex distribution (removes confounding)
Expressed as percentage or ratio relative to 1

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Reasons for collecting mortality data

Inform health services
Classify causes of death
Analyse patterns in mortality rate

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Define incidence

Number of new cases of a disease

Useful for monitoring epidemics

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Define prevalence

Number of people affected by disease (new and old)
Measures need for services
Measured as proportion not a rate
Does not take time into account

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Incidence rate calculation

Persons x time (years)

Define incidence rate ratio

Allows us to compare incidence rate of two groups with different levels of exposure
Exposed/unexposed
Compare efficacy of treatment

Define confounding factor

Links exposure to outcome but not on causative pathway

Common confounders

Ethnicity
Age
Sex

Define confidence interval

Range within which we can be 95% certain that the true value of the underlying tendency lies IR or SMR /x error factor X1000 to get per 1000 person years

Define null hypothesis

Default position No relationship between exposure and outcome 1

Define p value

Probability that the data observed is simply due to chance | <0.05 reject H0

Value lies within 95% confidence interval

Null hypothesis value of 1 lies in CI P>0.05 Results not statistically significant and could be due to chance Cannot reject null hypothesis

If null hypothesis value lies outside CI

Null hypothesis value of 1 does not lie in CI P<0.05 Results are statistically significant and unlikely due to chance Can reject null hypothesis

How to run a cohort study?

Recruit disease-free individuals Classify into exposed and unexposed Follow each group over time (years) Count how many develop the disease being studied Calculate the IR (d/p-y) for each group and then the IRR (relative risk)

Types of cohort studies

Concurrent (prospective) Historical (retrospective) Internal External

Define concurrent (prospective) study

Follow up starts immediately or later

Define historical (retrospective) study

Collect follow up data from the past

Define internal study

Between two subgroups | IRR

Define external study

Follow 1 group Compare to reference group SMR

Prospective vs retrospective

Retro quicker but may have unknown confounding | Because collecting data from past

Problems with external cohorts

Often limited data available for reference population Often no incidence data only mortality Study and ref population may not be comparable (selection bias)

Problems with internal cohort

Always smaller sample size and bigger error factor than external

Problems with cohort studies

``` Large and resource intensive Long time High loss to follow up (survivor bias) Not good for rare disease Possible unknown confounders ```

Case control study

Identify group of cases (diseased) Identify a suitable group of non-cases (controls) Establish previous exposure to causative agent Compare level of exposure in cases and controls(x6cases)

Odds ratio

Cases(dis) exposed x Unexposed controls(non dis) ----------------------------------------------------------- Controls exposed x cases unexposed

Types of bias

Selection Responder Survivor Information

When use IRR

Cohort

When use OR

Case controlled study

Cohort vs case control

``` Exposure basis Time n cost Rare disease n outcomes Range of d n o Bias n follow up Measure incidence ```

Exposure basis of study types

Cohort - compares outcomes based on exposure | Case-control exposure based on disease status

Cohort vs case control time n cose

Cohort large and time-consuming and so relatively expensive | Case-control quicker and relatively cheap

Cohort vs case control rare

Cohort not good for rare outcomes or diseases | Case-control not good for rare exposures

Cohort vs case control range disease

Cohort - study range of outcomes or diseases for each exposure Case-control - study range of exposures for each outcome/disease

Cohort vs case control bias

Cohort prone to losses to follow up | Case-control prone to selection and information bias

Types of information bias

Recall | Publication

Types of selection bias

Allocation | Healthy worker effect