Unit 4-5 Flashcards by Anabelle Ng

What is the difference between prevalence and incidence?

prevalence is a proportion while incidence is a risk/rate (dynamic)

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Number of students in a course who are sick vs number of students in a course who reported sick at any point over the semester describes what types of prevalence?

point vs period prevalence respectively

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Incidence x Duration = ?

prevalence (existing cases)

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The true rate. The speed at which new diseases or health outcomes occur is called the?

incidence rate

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What is the formula for incidence risk?

IR = (#of new cases in a specified time period) / [initial number at risk (NAR) - 1/2 (withdrawls)]

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To calculate incidence rate (IRR - incidence rate), there are two types of denominators. What are they?

Exact Denominator.

Approximate denominator.

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What is the exact denominator?

net time individuals in a population are at-risk during time

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What is the approximate denominator?

average number at risk (NAR) from start (NARinitial) to (NARfinal) - endof the follow up period
The average of these x internal time component *ITC)
this is the “true” rate

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What is the ITC?

internal time component:

equal to or less than time between initial and final measurements

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Crude vs Cause specific

to describes morbidity and mortality risk and rates

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Crude

captures all causes and types of disease and death

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Cause-specific

express level of disease or death caused by particular exposure/factor

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Crude risk

number developing any disease (morbidity) or dying (mortality) within specific period of time / number at risk minus 1/2 withdrawls

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Crude rate

number developing any disease (morbidity) or dying (mortality) within a specified period of time divided by average number at risk multiplied by internal time component

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Cause specific mortality rate

number dying of a specific disease within specified period of time divided by average number at risk multiplied by internal time component

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Case fatality “rate”

= (#who die from a particular disease) / (#who are sick from a disease)

it is used to measure mortality of particular disease

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Attack “rate”

= (#who get sick following a specific exposure) / (#who have that specific exposure)

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What are 3 measures of association?

Relative Risk
Odds Ratio
Incidence Risk Ratio

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If association is <1, how would you interpret this association?

negative association <1
no association = 1
positive association >1

remember these are ratios, so no difference between groups = 1

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What is the equation for relative risk?

= (risk of disease outcome in exposed group) / (risk of disease or outcome in non-exposed group)
= risk of disease E+ / risk of disease E-
= (a / (a+b)) / (c/(c+d))

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What is the equation for odds ratio?

= (odds of disease or outcome in exposed) / (odds of disease or outcome in non-exposed group)
= odds of disease in E+ / odds of disease in E-
=(a/b)/(c/d) = ad / bc

What is the equation for IRR?

= (incidence rate of outcome in exposed group) / incidence rate of the non-exposed group)
= (a1/t1) / (a0/t0)

What is risk or rate difference?

RD is the subtraction of background level of risk in the nonexposed group from exposed group
RD = risk or rate in exposed - risk or rate in non-exposed

What is risk difference for rates?

RD = a1/t1 - a0/t0

rate in E+ - rate in E-

What is the null value for RD?

0 if less than 0 then exposure is negatively associated if RD >0 positively associated RD = 0 then exposure has no differential effect on outcome

What does attributable proportion exposed (APe) express?

the proportion of risk/rate of outcome in exposed group that is attributable to specific exposure

APe is expressed in a percentage true or false.

true

Population Attributable Risk or Rate (PAR)

prevalence or rate of outcome in population - prevalence or rate of outcome in non-exposed group

Population Attributable Fraction

(PAR: prevalence of outcome in population - prevalence in nonexposed group) / (prevalence of outcome in population)

What are 4 reasons that census are impractical?

- time consuming - costly - tedious - difficult if participation is voluntary

What are 3 stages to sampling?

- Who/what to sample - How you're going to choose - How many you'll need to be confident

What are 2 criterias before sampling to choose subjects?

- inclusion criteria | - exclusion criteria

What is the difference between target, source, study/sample population?

Target population: population that you can extrapolate data from Source population: population from which study of subjects drawn Study/sampled population: group of sampling units that was selected from sampling frame

What is the sampling frame?

list of all study subjects in source population

What is the difference between internal and external validity?

Internal: degree to which observed findings in study lead to correct inferences about outcome of interest in source population External: degree to which inferences drawn from study can be generalized or extrapolated to broader population of interest

When every member of a source does not have equal probability of being selected, this is called...

non-probability sampling

What are the 3 types of non-probability sampling?

convenience sampling judgement sampling purposive sampling

What is purposive sampling?

when sampling units are chosen because of their exposure/disease status

What is judgement sampling?

investigator chooses what they think is representative of population

What are 5 types of probability sampling?

- simple random sampling - systematic random sampling - stratified random sampling - cluster sampling - multistage sampling

What is the difference between cluster and multistage sampling?

they are similar in which clusters/groups are chosen, but in cluster sampling all individuals are sampled whereas multistage, only a proportion of individuals are randomly selected and measured

What is systematic random sampling?

sampling at sampling intervals (every nth subject)

How do you calculate estimated variance for proportions?

p*q = p is proportions that have the disease * q is proportion of individuals that do not have the disease (1-P)

How do you calculate variance for means?

σ2 = Σ(x-x̄)2 / n note variance is equal to standard deviation squared

Zα

is the level of confidence | typically choose to have 95% confidence and 5% significance

The width of confidence intervals or how tight your confidence intervals are is the

precision. | range of values around sample estimate that includes the true value of sample proportion

What is "L"

allowable error = precision | i.e. accurate within 10% of true proportion

If there is a large association, it will be _____ to detect. If there is a small association, it will be _____ to detect

large association = easier to detect | small association = will be more difficult

Required sample size generally increases as....

- size of difference between two means or proportions decrease (smaller difference) - level of power to detect difference between two groups increases - number of confounding variables you are controlling for study increases - number of hypotheses testing increases

"cumulative incidence" is known as

incidence risk