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Pathology > Epidemiology > Flashcards

Epidemiology Flashcards

1
Q

How else can a discrete variable be categorised?

A

Count variable (i.e red cell count)

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2
Q

Which type of study would be the most appropriate to test the effect of a new statin on the incidence of coronary heart disease in patients with diabetes?

A

Randomised control trial

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3
Q

Which of the following methods cannot be used to compare the proportions in two sets of observations?

A

T test (difference between the two means)

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4
Q

What is prevalence?

A

How common a disease or condition occurs at a given time.

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5
Q

Prevalence calculation

A

(Number of diseased persons)/(Number of persons in the population) = Prevalence

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6
Q

What is relative risk?

A

The relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group.

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7
Q

What is absolute risk?

A

Absolute risk of a disease is your risk of developing the disease over a time period.

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8
Q

What is incidence?

A

Probability to develop the disease in a very small time interval

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9
Q

What is the observation period?

A

Observation period is the time from the start of the observation until the moment he/she develops disease.

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10
Q

How are incidence and prevalence correlated?

A

Incidence is positively correlated with prevalence

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11
Q

Types of observational studies

A 
Case report 
Case series 
Cross-sectional (prevalence)
Case control (retrospective)
Cohort (prospective)
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12
Q

Types of experimental studies

A

Interventional, RCTs

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13
Q

What is a case report?

A

Study of one individual with a disease, timely or rare information

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14
Q

What is a case series?

A

Study of several patients with similar symptoms. May lead to general hypothesis. No controls.

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15
Q

What is a cross sectional study?

A

Measures exposure and disease in study group at one time point (“snapshot”).

Frequently takes the form of survey, (e.g. questions about diagnosed coronary heart disease, family history, diet).

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16
Q

What is a cohort study?

A

Examines one or more health effects of exposure to a specific factor.

Subjects are defined according to their exposure status and followed over time to determine their health outcomes.

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17
Q

What is a case-control study?

A

Individuals who have the disease of interest are in a ‘case’ group, their exposure to specific factors are compared to a ‘control’ group from the same population sample

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18
Q

What is an ecological study?

A

Evaluates an association using the population rather than the individual as the unit of analysis. The rates of disease are examined in relation to factors described on the population level.

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19
Q

Two types of cohort studies?

A

Prospective, and retrospective

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20
Q

Prospective cohort study?

A

Exposure groups are followed into the future in order to observe the outcomes

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21
Q

Retrospective cohort study?

A

Both the exposures and outcomes have already occurred when the study begins.

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22
Q

What can RCTs calculate from results?

A

A risk

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23
Q

Can case control studies calculate risk?

A

No

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24
Q

What quantitative data can a case control study produce?

A

Odds ratio

25
Q

What is an odds ratio?

A

Probability that an event will occur divided by the probability that it will not occur

26
Q

Case control study table?

A

Cases and controls by exposed and unexposed

27
Q

Odds ratio from case control table?

A

exposed cases/unexposed cases = x

exposed controls/ unexposed controls = y

odds ratio = x/y

28
Q

Strengths of case control

A

Good for rare disease
Relatively fast
Relatively inexpensive
Can look at the association between the disease of interest and many kinds of exposures

29
Q

Weaknesses of case control

A

Susceptible to bias
May be hard to find suitable controls
Time relations may not be clear
Associations that are revealed may not be causal

30
Q

Relative risk calculation

A

Risk of developing a disease in the exposed group divided by the risk in the unexposed group.

31
Q

Relative risk table

A

Present/ absent disease by exposed/not exposed

32
Q

Relative risk calculation formula

A

exposed disease present / exposed present + absent

all over

not exposed disease present/ not exposed present + absent

33
Q

If RR = 1

A

There is no association between the factor under consideration and the disease.

34
Q

If RR<1

A

If RR < 1 there is a decreased risk of developing the disease if one is exposed to the factor under consideration.

35
Q

If RR>1

A

If RR > 1 there is an increased risk of developing the disease if one is exposed to the factor under consideration.

36
Q

Infection cycle needs?

A

An infectious source

Receptive susceptible host

Spread to further hosts - infection amplifies

37
Q

Incubation period

A

Time between catching an infection and symptoms appearing

38
Q

Latent period

A

Time between catching an infection and diagnostic signs (still asymptomatic)

39
Q

Infectious period

A

The time period during which an infected person is able to transmit the disease to a susceptible host or vector.

Not necessarily associated with symptoms

40
Q

What is basic reproduction rate (R0)?

A

R0 = the average number of persons infected by one disease source

41
Q

If R0 < 1

A

The disease will eventually disappear

42
Q

If R0 > 1

A

The disease will continue to spread

43
Q

R0 formula?

A

R0 = C x P x D

C: the number of contacts an infected person makes per unit time

P: the probability of transmission per contact

D: the duration the infected person is infectious to others

44
Q

Differences in transmission between enveloped and nonenveloped viruses

A

Non enveloped viruses are more virulent, because they don’t bud from the cell, they cause host cell lysis

45
Q

Non enveloped vs enveloped virus mode of transmission

A

Enveloped - secretions

Non-enveloped - faecal oral

46
Q

What are non-enveloped viruses resistant to and why?

A

Due to the protein shell, these viruses are resistant to heat, acids, and drying

47
Q

How does vaccination help the population?

A

Preventing people joining the Infectious Pool.

48
Q

What is pc?

A

The critical level of immunisation to eradicate the disease

49
Q

How is pc found

A

Calculating how far the proportion of susceptible has to be reduced in the face of an agent of a given Reproductive Rate, R0

The higher R0, the higher pc needs to be.

50
Q

pc calculation

A

pc=1−1/R0

51
Q

What is the most likely cause of the drop in disease incidence in vaccinated groups?

A

Immune protection

52
Q

What is the most likely cause of the drop in disease incidence in unvaccinated groups?

A

Herd immunity

53
Q

What is the most likely reason for a similar carbohydrate conjugate vaccine strategy to fail with another serotype of meningococcus?

A

The antigen for another serotype (B) may be too similar to a human antigen

54
Q

What does “a relative risk of 1.82” mean?

A

The risk for developing heart disease is 1.82 times greater (or 82% higher)

55
Q

What do you understand by “95% confidence interval 1.25 to 2.64”?

A

We are 95% certain that the true relative risk lies within the range 1.25-2.64

56
Q

When can we say risk is insignificant?

A

When confidence interval includes 1 (i.e no effect)

57
Q

Investigate whether a person’s sex was a risk factor for malaria. In their village, there
were exactly 400 adults.

120 men had experienced at least one episode of malaria, whereas eighty men had remained malaria-free. In contrast, 120 women were malaria-free and 80 had experienced malaria.

What was the malaria incidence rate in men?

A

120/200=0.6

58
Q

Investigate whether a person’s sex was a risk factor for malaria. In their village, there
were exactly 400 adults.

120 men had experienced at least one episode of malaria, whereas eighty men had remained malaria-free. In contrast, 120 women were malaria-free and 80 had experienced malaria.

What was the malaria incidence rate in women?

A

80/200 = 0.4

59
Q

Investigate whether a person’s sex was a risk factor for malaria. In their village, there
were exactly 400 adults.

120 men had experienced at least one episode of malaria, whereas eighty men had remained malaria-free. In contrast, 120 women were malaria-free and 80 had experienced malaria

What is the relative risk for men of malaria?

A

0.6/0.4

Pathology (21 decks)

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