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Nagasaki Flashcard Extravaganza > Epi/stats > Flashcards

Epi/stats Flashcards

1
Q

What three things does measuring disease frequency require?

A

WHAT: defining cases
WHO: the size of the population at risk
WHEN: The time point/period during which data are collected

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2
Q

What are the two measures of disease frequency and their definition?

A
  • Prevalence (prevalent cases): CURRENT CASES
  • Incidence (incident cases): the frequency (or number) of new occurrences DURING TIME FRAME
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3
Q

Name four type of descriptive data

A

Routine monitoring
Population census
Population survey
Descriptive study

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4
Q

What studies are analytical/observational?

A

Ecological
Cross sectional
Cohort
Case control

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5
Q

What are the analytical interventional studies?

A

RCT and non randomised

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6
Q

What do analytical studies aim to do?

A

Analytical aims to investigate which factors may be responsible for increasing or decreasing the probability (‘risk’) of an outcome.

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7
Q
A
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8
Q

The WHO made a list of 6 ‘building blocks’ required to build an adequate health system - what are they?

A
  1. Service Delivery
  2. Health Workforce
  3. Information about health needs
  4. Financing
  5. Medical leadership
  6. Adequate technology, equipment, vaccinations etc.
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9
Q

What are the current LMIC availabilities for WASH facilities in health care settings?

A

38% have no good water source
35% have no good soap source
19% have poor sanitation

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10
Q

What does the term ‘closed setting’ mean?

A

Closed setting: an area in which people are in a closed environment (e.g. refugee camp) living in extremely close proximity

high risk of rapid disease spread and epidemic

(in this vein, a slum might be a semi-closed setting, and a rural village may be considered an open setting)

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11
Q

What are the 4 most common causes of death in refugee camps?

A

Measles
Diarrhoea
Acute respiratory illness
Malaria

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12
Q

What s the ‘One Health’ Framework from the WHO?

A

Environmental Health
+
Human Health
+
Animal Health

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13
Q

What is the aim of blinding in an RCT?

A

To prevent:
- performance bias
- selection bias

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14
Q

How can you prevent skewed results from an Attrition Bias in an RCT?

A

An intention-to-treat (ITT) analysis

All patients are followed up re: outcomes/included in the trial regardless of whether their outcome

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15
Q

In regards to study outcomes, What is a dichotomous outcome? How is it statistically expresed?

A

An outcome where there are only two possibilities (e.g. mortality vs survival at one year)

They are summarised as:
Risks
Rates
Odds

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16
Q

What is Risk?

A

Outcome / Total Population

can be expressed as:
- a proportion (10 out of 100 people died),
- a decimal (0.1),
- a percentage (10%), or
- per unit population (100 per 1000 children)

(Because its literally just one of two outcomes)

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17
Q

What is the Odds?

A

Number of people WITH outcome / Number of people WITHOUT outcome

Should be described as a decimal or ratio

Should NOT be described as a percentage; percentage is the way we exclusively discuss risk

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18
Q

What is Risk Ratio (relative risk)

A

risk in the intervention group / risk in the control group

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19
Q

Which is expressed as a rate - incidence or prevalence?

A

incidence

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20
Q

What is incidence?

A

Number of new cases of a disease occurring in a given population over a given amount of time

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21
Q

What is prevalence?

A

The total number of people living with a disease at a specific moment in time.

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22
Q

What is a standardised mortality rate?

A

statistically constructed summary rates that account for the differences
between populations with respect
to other variables, such as age, sex
and race.

 An SMR of 100 means that people in the group are dying at the same rate as in the standard population
 SMR > 100 means death rates are higher, usually reflects worse health than average
 SMR < 100 means death rates are lower, usually means health is better than average in this area
 E.g. SMR of 168 in area A means death rates in area A are 68% higher than in standard population

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23
Q

What are three examples of descriptive studies

A

 Correlational (ecological) study
 Case reports / case series
 Cross sectional studies (surveys)

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24
Q

What are three examples of Analytical studies?

A

 Cohort
 Case control
 Intervention e.g. RCT

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25
Q

Name 2 advantages and 2 disadvantages of a cohort study?

A

ADVANTAGES
- Low risk of bias
- Good for looking at rare exposures
- can assess the effects of multiple exposures at the same time
- Can get a temporal (time
related) sequence between
exposure and outcome as all
individuals must be free of
disease at the beginning of the
study.

DISADVANTAGES
- can take a long time
- Loss to follow up (this can lead to attrition bias)
- expensive and resource intensive
- bad for looking at rare diseases

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26
Q

What is a case control study?

A

 A group of people with a disease are compared to a group without the disease from the same population.
e.g. men in their 50s who have hypertension vs. men in their 50s who do not

 Compare exposure to risk factors in both groups

 Able to look at many different possible risk factors

 Able to study diseases with a long latency period

 Most common analytic study design seen in medical literature today

 Particularly susceptible to bias

 Comparatively less expensive

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27
Q

Give one advantage and one disadvantage of an RCT?

A

PROS:
- Gold standard
- provides powerful evidence on the effect an intervention has on an outcome

CONS:
- hard to get ethical approval
- expensive
- difficult to design and conduct

28
Q

What is positive and negative predictive value?

A

The positive and negative predictive values (PPV and NPV respectively) are the proportions of positive and negative results in statistics and diagnostic tests that are true positive and true negative results, respectively.

29
Q

What is sensitivity?

A

Sensitivity (true positive rate) is the probability of a positive test result, conditioned on the individual truly being positive.

30
Q

What is specificity?

A

Specificity (true negative rate) is the probability of a negative test result, conditioned on the individual truly being negative

31
Q

Calculate PPV

A

True positive/True positive and false positive

32
Q

Calculate NPV

A

False negative/True negative+False negative

33
Q

Calculate sensitivity

A

True positive/ True positive+False negative

34
Q

Calculate specificity

A

True negative/True negative+False positive

35
Q

What is a case control study?

A

Starts with two comparison groups, one of which already has the condition at the beginning

36
Q

What is a cohort study?

A

Compares two groups neither of which have the condition at the beginning

37
Q

Cut off p-value for significance?

A

Usually <0.05, better when <0.01

38
Q

Calculate NNT

A

1/ARR

39
Q

Calculate ARR

A

ARR = event rate of control - event rate of intervention

40
Q

Calculate odds ratio

A

Look at which is the event they want ORR on
(A/B) / (C/D)
Used for case control

41
Q

Calculate relative risk

A

Look at which is the event they want ORR on
(A/A+B) / (C/C+D)
Used for cohort

42
Q

How many patients captured by one standard deviation?

A

68%

43
Q

How many patients captured by two standard deviations?

A

95%

44
Q

What is in level of evidence 1?

A

Meta analysis
Systematic review
RCT

45
Q

What trials are prospective?

A

RCT
Cohort

46
Q

What are descriptive studies?

A

Case reports
Case series
Qualitative reports
Surveys

47
Q

What are analytic studies?

A

2 main types of analytic studies based on whether the intervention was randomly allocated
If yes -> RCT
If no -> observational study (cohort, case control, cross sectional)

48
Q

What are the observational studies?

A

Cohort, case control, cross sectional

49
Q

Advantages and disadvantages of cohort?

A

Advantages:
ethically safe;
subjects can be matched;
can establish timing and directionality of events
administratively easier and cheaper than RCT

Disadvantages:
controls may be difficult to identify;
exposure may be linked to a hidden confounder;
blinding is difficult;
randomisation not present;
for rare disease, large sample sizes or long follow-up necessary.

50
Q

Advantages and disadvantages of case control study

A

Advantages:
- quick and cheap;
- only feasible method for very rare disorders or those with long lag between - - exposure and outcome;
- fewer subjects needed than cross-sectional studies

Disadvantages:
- reliance on recall or records to determine exposure status;
- confounders;
- selection of control groups is difficult;
- potential bias: recall, selection

51
Q

what are the advantage and disadvantages of a cross sectional study?

A

Advantages:
- cheap and simple;
- ethically safe

Disadvantages:
- establishes association at most, not causality;
- recall bias susceptibility;
- confounders may be unequally distributed;
- Neyman bias;
- group sizes may be unequal.

Good for prevelance of disease or risk factor

52
Q

What are the advantages and disadvantages of a RCT?

A

Best for intervention effect

Advantages:
- unbiased distribution of confounders
- blinding more likely
- randomisation facilitates statistical analysis

Disadvantages:
- expensive: time and money
- volunteer bias
- ethically problematic at times

53
Q

What are clinical trial phases?

A

Clinical Trial Phases
0 – human microdosing studies
1 – healthy people
2 – people with relevant illness in lab setting
3 – people with illness in clinical setting
-> Marketing authorization
4 – post-marketing surveillance studies

54
Q

How many patients are captured by three standard deviations?

A

99.7%

55
Q

What is a “very highly signficant” p value

A

P = 0.001 – “very highly signficant”
The probability of a difference this large happening by chance in 0.001 in 1 (1 in 1000)

56
Q

What is likelihood ratio?

A

LR + is the multiplier for how much more likely the patient is to have the condition if the test result is positive

57
Q

How is correlation calcuated?

A

Calculated using Pearson correlation coefficient if data is sampled from “normal” populations
Otherwise Spearmans rank correlation coefficient is used

58
Q

what is the CONSORT statement

A

an evidence-based, minimum set of recommendations for reporting RCTs.

A standard way for researchers to prepare reports of their trial findings
Facilitating complete and transparent reporting
Aiding critical appraisal and interpretation

59
Q

How can the relationship between incidence and prevalence be approximated

A

Prevalence = incidence x average duration

60
Q

what does a relative risk of <1 mean

A

Relative risk value of less than 1.0

= an inverse association

= a decreased risk among the exposed group

i.e. the exposure is protective

61
Q

what does a relative risk of >1 mean

A

Relative risk > 1.0

Indicates a positive association

An increased risk among the exposed group

62
Q

What happens to the PPV as the prevelance of the infection drops

A

PPVs become lower as prevalence drops

63
Q

What are the levels of evidence in EBM?

A

Level I: Evidence from a systematic review of all relevant randomized controlled trials. Level II: Evidence from a meta-analysis of all relevant randomized controlled trials. Level III: Evidence from evidence summaries developed from systematic reviews.

64
Q

What is an epidemic or outbreak?

A

Disease occurrence among a population that is in excess of what is expected in a given time or place

65
Q

What is a cluster?

A

Group of cases in a specific time or place that might be more than expected

66
Q

What does endemic mean?

A

A disease or condition which is always present

67
Q

What is a pandemic?

A

A disease or condition which is spreading across regions

Nagasaki Flashcard Extravaganza (33 decks)

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