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Year 2 > Statistics > Flashcards

Statistics Flashcards

(62 cards)

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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
If we have not normally distributed data, what test do we use to find out if they are from two different populations?
Mann-Whitney rank test
26
What test do we use for parametric data?
Students t-test
27
What test do we use for non-parametric data?
Mann Whitney rank test
28
What is parametric data?
Normally distributed data
29
What is non-parametric data?
Not normally distributed data
30
What is a type I error?
Rejecting the null hypothesis when it is true (Thinking something is happening when it isn’t)
31
What is a type II error?
Accepting the null hypothesis when it is not true (Thinking nothing is happening when it is)
32
What test do you use for categorical independent data and the dependant variable is continuous?
T test Mann whitney
33
What test do you use for observations that are paired?
Paired t test (for 2 groups) General linear (more than 2)
34
What test do you use where both dependant and independent variables are continuous?
Linear regression (parametric) Spearman rank test (non-parametric)
35
What test do you use where the dependant variable is categorical?
Chi square
36
What is the incidence rate?
New cases that occur over time (Number of new cases/total animal time at risk)
37
What is the denominator population?
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
What is prevalence?
A proportion of a population with a certain disease at a particular point in time
39
What is passive surveillance?
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
What is active surveillance?
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
What is random sampling?
Equal approach to ensure every member of the population has an equal chance of being included
42
What is stratified random sampling?
Sampling randomly within defined strata in the data set - every 7th cat
43
What is standard error?
A measure of uncertainty in an estimate from a sample
44
What is the standard error of the mean?
How close the mean of your sample is to the true mean of the population (Mean gets smaller as sample size increases)
45
What is bias?
A systematic error that leads to results that are consistently too large or too small
46
What is the confidence interval?
Range of values that are believed to contain the trite parameter value (should be 95%)
47
Why design a study?
To be sure about efficacy To determine a risk factor Applicable to rest of the population Avoid bias
48
What are the 4 main study types?
Cross sectional Cohort Case control Randomised controlled trials
49
What is a cross sectional study?
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
What is a cohort study?
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
What is a case control study?
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
What is a randomised controlled trial?
Planned experiment See if treatment has an effect Population must be cases 2 groups: treated or non treated
53
What are the 3 types of randomised controlled trials?
Single blind: don’t know what treatment they receive Double blind: operator also doesn’t know Triple blind: statistician also doesn’t know
54
What is the hierarchy of evidence tool?
It shows that some studies had better weighted evidence compared to others
55
What are two types of bias?
Selection bias Confounding bias
56
What is selection bias?
Occurs before the study begins Sample selection doesn’t represent target population
57
What are examples of selection bias?
Choice of comparison groups Non response bias Missing data Loss to follow up Healthy worker effect
58
What is confounding bias?
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
What is an example of confounding bias?
Diagnostic test with imperfect sensitivity or specificity
60
How are diagnostic tests’ performance measured?
Sensitivity Specificity
61
What is sensitivity?
The probability that an animal with the disease is identified by the test The number of positives detected
62
What is specificity ?
The probability that an animal without the disease is tested negative by the test

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