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POPM*3250 > Unit 4-5 > Flashcards

Unit 4-5 Flashcards

1
Q

What is the difference between prevalence and incidence?

A

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

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2
Q

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?

A

point vs period prevalence respectively

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3
Q

Incidence x Duration = ?

A

prevalence (existing cases)

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4
Q

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

A

incidence rate

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5
Q

What is the formula for incidence risk?

A

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

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6
Q

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

A

Exact Denominator.

Approximate denominator.

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7
Q

What is the exact denominator?

A

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

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8
Q

What is the approximate denominator?

A

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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9
Q

What is the ITC?

A

internal time component:

equal to or less than time between initial and final measurements

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10
Q

Crude vs Cause specific

A

to describes morbidity and mortality risk and rates

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11
Q

Crude

A

captures all causes and types of disease and death

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12
Q

Cause-specific

A

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

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13
Q

Crude risk

A

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

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14
Q

Crude rate

A

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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15
Q

Cause specific mortality rate

A

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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16
Q

Case fatality “rate”

A

= (#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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17
Q

Attack “rate”

A

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

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18
Q

What are 3 measures of association?

A
  • Relative Risk
  • Odds Ratio
  • Incidence Risk Ratio
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19
Q

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

A

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

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

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20
Q

What is the equation for relative risk?

A

= (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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21
Q

What is the equation for odds ratio?

A

= (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

22
Q

What is the equation for IRR?

A

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

23
Q

What is risk or rate difference?

A

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

24
Q

What is risk difference for rates?

A

RD = a1/t1 - a0/t0

rate in E+ - rate in E-

25
Q

What is the null value for RD?

A

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

26
Q

What does attributable proportion exposed (APe) express?

A

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

27
Q

APe is expressed in a percentage true or false.

A

true

28
Q

Population Attributable Risk or Rate (PAR)

A

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

29
Q

Population Attributable Fraction

A

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

30
Q

What are 4 reasons that census are impractical?

A
  • time consuming
  • costly
  • tedious
  • difficult if participation is voluntary
31
Q

What are 3 stages to sampling?

A
  • Who/what to sample
  • How you’re going to choose
  • How many you’ll need to be confident
32
Q

What are 2 criterias before sampling to choose subjects?

A
  • inclusion criteria

- exclusion criteria

33
Q

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

A

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

34
Q

What is the sampling frame?

A

list of all study subjects in source population

35
Q

What is the difference between internal and external validity?

A

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

36
Q

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

A

non-probability sampling

37
Q

What are the 3 types of non-probability sampling?

A

convenience sampling
judgement sampling
purposive sampling

38
Q

What is purposive sampling?

A

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

39
Q

What is judgement sampling?

A

investigator chooses what they think is representative of population

40
Q

What are 5 types of probability sampling?

A
  • simple random sampling
  • systematic random sampling
  • stratified random sampling
  • cluster sampling
  • multistage sampling
41
Q

What is the difference between cluster and multistage sampling?

A

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

42
Q

What is systematic random sampling?

A

sampling at sampling intervals (every nth subject)

43
Q

How do you calculate estimated variance for proportions?

A

p*q

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

44
Q

How do you calculate variance for means?

A

σ2 = Σ(x-x̄)2 / n

note variance is equal to standard deviation squared

45
Q

Zα

A

is the level of confidence

typically choose to have 95% confidence and 5% significance

46
Q

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

A

precision.

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

47
Q

What is “L”

A

allowable error = precision

i.e. accurate within 10% of true proportion

48
Q

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

A

large association = easier to detect

small association = will be more difficult

49
Q

Required sample size generally increases as….

A
  • 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
50
Q

“cumulative incidence” is known as

A

incidence risk

POPM*3250 (4 decks)

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