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Year 2 > Statistics > Flashcards

Statistics Flashcards

1
Q

Risk definition

A

The probability of an event happening in a given period of time

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2
Q

Odds definition

A

The ratio of the probability an event will happen to the probability of it not happening

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3
Q

Absolute risk definition

A

The likelihood of an event occurring under specific conditions (risk of developing disease over time)

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4
Q

Relative risk definition

A

Likelihood of an even occurring when in comparison to another event (comparing the likelihood of getting a disease when exposed vs not being exposed)

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5
Q

Prevalence definition

A

Proportion of a population with a characteristic (disease) at a particular point in time

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6
Q

What information do you need to measure the outcome of absolute risk?

A

Incidence
Prevalence
Odds
Hazard ratio

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7
Q

What information do you need to measure the outcome of relative risks?

A

Risk ratio
Odds ratio
Hazard ratio

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8
Q

Risk example question: “the risk of obesity in bull terriers: total 334 sampled & 20 confirmed obese”
Work out the risk.

A

20/334 = 0.0599 = 6% of bull terriers obese

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9
Q

Odds example question: “20 obese SBT out of 334 dogs” work out the odds.

A

334-20 = 314 not obese
Odds = 20/314 = 0.064 = 6%

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10
Q

What are the pros and cons to using risk ratios?

A

More accurate reflection of population
Easier to interpret

  • harder to calculate
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11
Q

What are the pros and cons to using odds ratio?

A

Simple to calculate
Can make decisions from results
Info of one outcome vs another

  • can’t estimate prevalence of disease
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12
Q

Confidence interval definition

A

95%
Range of values which contain the true parameter value
Within 2 SD (standard deviations)
If repeated would have same results
Only with normal distributed data

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13
Q

What is the P value to be considered statistically significant?

A

<0.05%

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14
Q

What graph should be used to display categorical data?

A

Bar chart

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15
Q

What graph should be used to display continuous data?

A

Histogram

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16
Q

What graph should be used to display median and interquartile ranges?

A

Box & whisker plot

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17
Q

What can graphs be used to identify?

A

General shape of data (bell curve; positive correlation etc)
Centre of distribution (avg.)
It’s spread
Outliers
Relationships between 2 variables

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18
Q

What percentage does 1SD equivalate to?

A

68%

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19
Q

What percentage does 2SD equivalate to?

A

95%

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20
Q

What percentage does 3SD equivalate to?

A

99%

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21
Q

What is a dependent variable? & what axis is it plotted on?

A

The thing you measure
Y axis

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22
Q

What is an independent variable? & what axis is it plotted on?

A

The thing you are changing
X axis

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23
Q

What is the Null hypothesis?

A

States there is no effect or difference (and assumes the scientific hypothesis is true)

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24
Q

If we have normally distributed data, what test do we use to find out if they are from two different populations?

A

Students t-test

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25
Q

If we have not normally distributed data, what test do we use to find out if they are from two different populations?

A

Mann-Whitney rank test

26
Q

What test do we use for parametric data?

A

Students t-test

27
Q

What test do we use for non-parametric data?

A

Mann Whitney rank test

28
Q

What is parametric data?

A

Normally distributed data

29
Q

What is non-parametric data?

A

Not normally distributed data

30
Q

What is a type I error?

A

Rejecting the null hypothesis when it is true
(Thinking something is happening when it isn’t)

31
Q

What is a type II error?

A

Accepting the null hypothesis when it is not true
(Thinking nothing is happening when it is)

32
Q

What test do you use for categorical independent data and the dependant variable is continuous?

A

T test
Mann whitney

33
Q

What test do you use for observations that are paired?

A

Paired t test (for 2 groups)
General linear (more than 2)

34
Q

What test do you use where both dependant and independent variables are continuous?

A

Linear regression (parametric)
Spearman rank test (non-parametric)

35
Q

What test do you use where the dependant variable is categorical?

A

Chi square

36
Q

What is the incidence rate?

A

New cases that occur over time
(Number of new cases/total animal time at risk)

37
Q

What is the denominator population?

A

The number of individuals in the population at the start of the observation period, I.E., how many cows do you have in total?

38
Q

What is prevalence?

A

A proportion of a population with a certain disease at a particular point in time

39
Q

What is passive surveillance?

A

Uses existing data
No defined population
No defined unit of measure
Misses subclinical cases
Not all owners will take to vet to report
Owners may not allow samples
Relies on reporting and routine data

40
Q

What is active surveillance?

A

Active looking/collection of disease info
May miss new diseases - looking for specific ones
Screen unwell & healthy ones
Systemic detection of cases
Comparable data time or area
Expensive and time consuming

41
Q

What is random sampling?

A

Equal approach to ensure every member of the population has an equal chance of being included

42
Q

What is stratified random sampling?

A

Sampling randomly within defined strata in the data set - every 7th cat

43
Q

What is standard error?

A

A measure of uncertainty in an estimate from a sample

44
Q

What is the standard error of the mean?

A

How close the mean of your sample is to the true mean of the population
(Mean gets smaller as sample size increases)

45
Q

What is bias?

A

A systematic error that leads to results that are consistently too large or too small

46
Q

What is the confidence interval?

A

Range of values that are believed to contain the trite parameter value (should be 95%)

47
Q

Why design a study?

A

To be sure about efficacy
To determine a risk factor
Applicable to rest of the population
Avoid bias

48
Q

What are the 4 main study types?

A

Cross sectional
Cohort
Case control
Randomised controlled trials

49
Q

What is a cross sectional study?

A

Surveys, lab experiments
Snapshot of information at one point in time
Can calculate prevalence, relative risk and attributable risk
Cannot differentiate cause and effect

50
Q

What is a cohort study?

A

Follow target group for period of time
Compare outcomes in exposed and non-exposed environment
Measures incidence rate, relative risk, attributable risk
Monitor several diseases simultaneously
Estimate disease incidence
Determines causality
Need large population
Long time
Costly

51
Q

What is a case control study?

A

2 groups: cases & controls
Accurate & consistent case definition
Calculate using odds ratio
Can study rare diseases
Get background info quickly
Liable to bias
Can’t estimate disease incidence

52
Q

What is a randomised controlled trial?

A

Planned experiment
See if treatment has an effect
Population must be cases
2 groups: treated or non treated

53
Q

What are the 3 types of randomised controlled trials?

A

Single blind: don’t know what treatment they receive

Double blind: operator also doesn’t know

Triple blind: statistician also doesn’t know

54
Q

What is the hierarchy of evidence tool?

A

It shows that some studies had better weighted evidence compared to others

55
Q

What are two types of bias?

A

Selection bias
Confounding bias

56
Q

What is selection bias?

A

Occurs before the study begins
Sample selection doesn’t represent target population

57
Q

What are examples of selection bias?

A

Choice of comparison groups
Non response bias
Missing data
Loss to follow up
Healthy worker effect

58
Q

What is confounding bias?

A

Mixing together the effects of two or more factors that are related to each other and the outcome.

Will chase incorrect classification of outcome and exposure

59
Q

What is an example of confounding bias?

A

Diagnostic test with imperfect sensitivity or specificity

60
Q

How are diagnostic tests’ performance measured?

A

Sensitivity
Specificity

61
Q

What is sensitivity?

A

The probability that an animal with the disease is identified by the test

The number of positives detected

62
Q

What is specificity ?

A

The probability that an animal without the disease is tested negative by the test

Year 2 (4 decks)

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