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INF > ANALYTICAL STUDIES AND KEY STATISTICAL CONCEPTS > Flashcards

ANALYTICAL STUDIES AND KEY STATISTICAL CONCEPTS Flashcards

1
Q

ROLE AND CHARACTERISTICS OF ANALYTICAL STUDIES?

A
  • AN ANALYTICAL STUDY ALLOWS TESTING OF HYPOTHESES AND ESTIMATION OF THE RISK OF A CERTAIN ILLNESS
  • THEY ARE ALWAYS OBSERVATIONAL (I.E. NO INTERVENTION IS IMPLEMENTED LIKE IN RANDOMISED CONTROL TRIALS)
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2
Q

WHY ARE EPIDEMIOLOGICAL STUDIES DONE?

A
  • TO UNDERSTAND WHAT HAPPENED
  • TO ESTIMATE THE EXTENT OF THE OUTBREAK
  • TO IDENTIFY THE POTENTIAL SOURCE (SO IT CAN BE CONTROLLED AND PREVENTED IN THE FUTURE)
  • TO CREATE EVIDENCE AND KNOWLEDGE
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3
Q

ROLE OF EPIDEMIOLOGICAL STUDIES (ANALYTICAL EPIDEMIOLOGY)?

A

THEY CAN GIVE AN IDEA OF HOW LIKELY IT IS THAT AN EXPOSURE IS ASSOCIATED WITH ILLNESS
(THEY CAN TEST THE HYPOTHESIS GENERATED BY DESCRIPTIVE EPIDEMIOLOGY)

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4
Q

WHAT IS RISK IN EPIDEMIOLOGY?

A
  • THE PROBABILITY AN EVENT WILL OCCUR
  • THE PROPORTION OF INITIALLY DISEASE FREE INDIVIDUALS WHO DEVELOP DISEASE OVER A DEFINED PERIOD OF OBSERVATION
  • DEFINITION OF RISK HERE DOESN’T INCLUDE PERCEPTIONS OF RISK AS E.G. DANGEROUS SITUATIONS (THOSE ARE JUST SUBJECTIVE JUDGEMENTS)
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5
Q

2 MAIN TYPES OF ANALYTICAL STUDIES?

A

COHORT STUDY AND CASE CONTROL STUDY

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6
Q

WHAT IS A COHORT IN EPIDEMIOLOGICAL TERMS?

A

A GROUP OF PEOPLE WITH SOMETHING IN COMMON, USUALLY AN EXPOSURE (SAME EXPERIENCE IN THE SAME PERIOD OF TIME)

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7
Q

WHICH ANALYTICAL STUDY DESIGN IS USUALLY USED WHEN OUTBREAK INVESTIGATION IS DONE FOR A DEFINED POPULATION?

A

COHORT STUDY

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8
Q

WHAT ARE THE OUTPUTS OF COHORT STUDIES, I.E. WHAT CAN BE CALCULATED?

A
  • ATTACK RATE (RISK)

- RISK RATIO/RELATIVE RISK (RR)

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9
Q

EXAMPLES OF WHEN COHORT STUDIES MIGHT BE USED?

A
  • WEDDINGS, BBQs..
  • EVENTS WHERE THERE IS A GUEST LIST (IF TOO BIG A COHORT STUDY WON’T BE POSSIBLE, RESOURCES NEED TO BE CONSIDERED)
  • EVENTS WHERE IT CAN USUALLY BE IDENTIFIED WHO BECOME ILL, WHERE THE MENU WAS LIMITED ETC
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10
Q

INTERPRETATION OF RELATIVE RISK/RISK RATIO (RR):

A

RR>1 RISK FACTOR
RR=1 NO ASSOCIATION
RR<1 PROTECTIVE FACTOR

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11
Q

WHAT IS ATTACK RATE AND HOW IS IT CALCULATED?

A
  • AKA RISK
  • THE PROPORTION OF PEOPLE WHO BECAME ILL WITH A DISEASE IN A POPULATION INITIALLY FREE OF THE DISEASE
    (NUMBER OF CASES/TOTAL NUMBER OF PARTICIPANTS)x100
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12
Q

HOW IS ATTACK RATE (RISK) USED IN COHORT STUDIES?

A

FOR EACH EXPOSURE OF INTEREST, WHEN CAL CALCULATE ATTACK RATE IN EXPOSED AND IN UNEXPOSED PARTICIPANTS AND USE THEM WHEN DETERMINING THE RR

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13
Q

WHAT IS RELATIVE RISK/RISK RATIO AND HOW IS IT CALCULATED?

A

A RATIO OF THE EXPOSED AND UNEXPOSED ATTACK RATES

RISK OF DISEASE IN EXPOSED/RISK OF DISEASE IN UNEXPOSED

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14
Q

WHAT DOES A RISK RATIO DETERMINE?

A

IT DETERMINES IF THE ATTACK RATE IN THE EXPOSED INDIVIDUALS IS HIGHER THAN IN THE UNEXPOSED AND BY HOW MANY TIMES (HELPS DETERMINE RISK FACTORS AND PROTECTIVE FACTORS)

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15
Q

WHEN ARE CASE CONTROL STUDIES USED IN EPIDEMIOLOGY AND HOW ARE PARTICIPANTS SELECTED?

A
  • WHEN THERE’S NO DEFINED POPULATION; E.G. INCREASE IN CASES IN A PARTICULAR GEOGRAPHICAL AREA
  • ALL CASES ARE INCLUDED AND THEN CONTROLS ARE SELECTED (CONTROLS NEED TO BE FROM THE SAME POPULATION); BOTH ARE ASKED THE SAME QUESTIONS
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16
Q

WHAT IS THE OUTPUT OF A CASE CONTROL STUDY?

A

AN ODDS RATIO

17
Q

WHAT DOES AN ODDS RATIO DETERMINE?

A

THE DIFFERENCE OF THE FREQUENCY OF EXPOSURE BETWEEN CASES AND CONTROLS

18
Q

INTERPRETING ODDS RATIO:

A

OR>1 RISK FACTOR
OR=1 NO ASSOCIATION
OR<1 PROTECTIVE FACTOR

19
Q

EXAMPLES OF WHEN CASE CONTROL STUDIES ARE USED?

A
  • NATIONALLY DISPERSED OUTBREAKS ASSOCIATED WITH FOOD
  • TAKE-AWAYS
  • MOST OUTBREAKS
20
Q

DEFINITION OF THE P VALUE?

A

THE PROBABILITY OF OBTAINING RESULTS AT LEAST AS EXTREME AS THE OBSERVED RESULTS, ASSUMING THAT THE NULL HYPOTHESIS IS CORRECT

21
Q

WHAT IS THE NULL HYPOTHESIS IN EPIDEMIOLOGY?

A

THE HYPOTHESIS STATING THERE IS NO ASSOCIATION BETWEEN THE CASES AND THE EXPOSURE; STATES THERE IS NO DIFFERENCE BETWEEN OBSERVED GROUPS

22
Q

RANGE OF VALUES THE P VALUE CAN TAKE?

A

A NUMBER BETWEEN 0 AND 1

23
Q

WHEN DOES P VALUE INDICATE STATISTICAL SIGNIFICANCE?

A

WHEN IT IS LOW; USUALLY <0.05 (5%)

INDICATES THAT THE ASSOCIATION IS LIKELY AND WE CAN REJECT THE NULL HYPOTHESIS

24
Q

WHEN TESTING A HYPOTHESIS, WHAT DOES THE P VALUE TELL US ABOUT THE RESULTS WE GET?

A

IT HELPS DETERMINE THE STATISTICAL SIGNIFICANCE OF THE RESULTS

25
Q

WHEN CAN’T YOU REJECT THE NULL HYPOTHESIS?

A

WHEN p>0.05

26
Q

WHAT DO P VALUES DEPEND ON?

A
  • SIZE OF THE EFFECT

- SIZE OF THE SAMPLE

27
Q

HOW DOES SAMPLE SIZE INFLUENCE THE P VALUE AND HOW IS THIS ADDRESSED?

A
  • IF THE SAMPLE IS LARGE ENOUGH, EVEN VERY SMALL DIFFERENCES WILL BE CONSIDERED ‘STATISTICALLY SIGNIFICANT’
  • THAT’S WHY P VALUE IS OFTEN ACCOMPANIED BY CONFIDENCE INTERVALS WHICH ARE MORE INFORMATIVE
28
Q

WHAT ARE CONFIDENCE INTERVALS (IN ANALYTICAL STUDIES)?

A

RANGES OF POTENTIAL VALUES FOR THE OR & RR AS THEY ARE BOTH ESTIMATES CALCULATED FROM A SAMPLE; CI INDICATE THE PRECISION WITH WHICH THE SAMPLE ESTIMATE IS LIKELY TO REPRESENT THE POPULATION FROM WHICH THAT SAMPLE WAS DRAWN

29
Q

WHAT DOES A NARROW CONFIDENCE INTERVAL IMPLY?

A

A LARGE SAMPLE SIZE OR THAT THE RESULTS WERE VERY SIMILAR/PRECISE

30
Q

INTERPRETING CONFIDENCE INTERVALS FOR OR AND RR:

A

WHERE A 95% CONFIDENCE INTERVAL INCLUDES 1 THERE IS NO EVIDENCE AT THE LEVEL OF P=0.05 THAT THERE IS A TRUE DIFFERENCE (THAT A HYPOTHESIS ALTERNATIVE TO NULL HYPOTHESIS IS CORRECT)

31
Q

WHAT IS A CONFOUNDER IN EPIDEMIOLOGY?

A

SOMETHING ASSOCIATED WITH BOTH EXPOSURE AND THE OUTCOME

32
Q

WHAT IS MULTIVARIABLE ANALYSIS IN EPIDEMIOLOGY?

A
  • ANALYSIS LOOKING AT ASSOCIATIONS FOR SEVERAL X VARIABLES (EXPOSURES) SIMULTANEOUSLY, BUT ONLY ONE Y (ILLNESS)
    . MANY DIFFERENT STATISTICAL TECHNIQUES ARE USED, REGRESSION BEING THE MOST COMMON
33
Q

WHAT IS THE ROLE OF ADJUSTED ODDS RATION aOR?

A

IT PRODUCES THE ODDS RATIO FOR EACH INDIVIDUAL VARIABLE ASSUMING THAT THE OTHER VARIABLES WERE HELD CONSTANT

34
Q

WHAT ARE THE AIMS OF THE MULTIVARIABLE ANALYSIS?

A
  • UNDERSTAND WHICH VARIABLES ARE ASSOCIATED WITH AN OUTCOME
  • ACCOUNT FOR THE EFFECT OF THE OTHER VARIABLES WHEN MEASURING ONE VARIABLE
  • ADJUST FOR ‘CONFOUNDERS’
35
Q

WHAT ARE ZOONOSES?

A
  • INFECTIOUS DISEASES WHICH JUMPED FROM A NON-HUMAN ANIMAL TO HUMANS
  • THEY SPREAD TO HUMANS THROUGH DIRECT CONTACT OR THROUGH FOOD, WATER OR THE ENVIRONMENT
  • CAUSES CAN BE BACTERIA, VIRUSES, PARASITES AND OTHER UNCONVENTIONAL AGENTS LIKE PRIONS
  • SOME DISEASES CAN BEGIN AS ZOONOSIS BUT MUTATE TO BECOME HUMAN ONLY (LIKE HIV)
36
Q

MEANING OF ONE HEALTH APPROACH WHEN ADDRESSING ZOONOSES?

A
  • CONTROL REQUIRES CO-OPERATION OF HUMAN, ENVIRONMENTAL AND ANIMAL HEALTH PARTNERS
  • IMPOSSIBLE FOR JUST ONE PERSON/ORGANISATION/SECTOR ALONE TO ADDRESS THE ANIMAL-HUMAN-ENVIRONMENT INTERFACE ADEQUATELY

INF (40 decks)

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