Statistics Flashcards
Difference between incidences and prevalence?
Incidence - Rate new cases arising
Prevalence - N of cases at time of counting
Difference risk and odd
Think tossing a coin
Risk: 1/2 = 0.5
Odds: 1/1 = 1 Number time event occurs
What type of studies used to calculate risk ratio/relative risk
Large cohort study. Large population set with exposed and non exposed group. Compare number of outcomes in each group.
Using table show how you calculaterisk ratio/relative risk
What types of studies are used to calculate odds ratio?
Retrospective or case-control studies
Smaller data set
Using table explain how odds ratio calculated
For either RR or OR what is the meaning
1
>1
<1
1 = No difference
>1 = Exposure likely risk factor
< 1 = Exposure likely protective
If the CI crosses which numerical value does that mean there is no statistic significance for
1) risk and odds ratios
2) means/percetnage/medians
1) 1
2) 0
Draw a table to explain type 1, type 2 errors
How to increase the power of a study>
The power of a study increases as the chances of commingling a Type 2 error decreases
1-beta
Power usually set to 80%, accepting 20% of the time we will miss a real difference
Flow chart to work out statistical test
What is the ability of a test to detect disease?
Sensitivity
TP/TP+FN
What is the ability of a test to exclude the presence of a disease when it is not truly present?
Specificity
TN/TN+FP
Which test – the probability that an individual with the +ve test has or will develop the disease
PPV
TP/TP+FP
which test - the probability that a subject with a negative test result actually does not have the disease
NPP
TN/TN+FN
Table showing calculations sensitivity, specificity,postive predictive value and negative predictive value
What is the positive likelihood ration
sensitivity/(1-specificity)
What is the negative likelihood ration
specificity/(1-sensitivity)
How doe likelihood ratios impact post-test probability of disease?
How to calculate perinatal mortality rate?
Total number of deaths fetal deaths from 20 weeks/livebirth + stillbirth in 1 year x 1,000
How to calculated neonatal mortality rate?
N of children doing <28days/liver births in a year x 1000
Post-neonatal death
After 28 days but before 1 year
How to calculate infant mortality rate?
Number of newborns dying < 1 year/number of live births x1,000
What is needed to calculate sample size?
- Current response rate
- Estimated difference in response rates
- 1 or 2 tailed
- p-value
- power
What is standard deviation?
Square root of the variance
Most common measure of spread
How to calculate varience
In standard deviation, what % is 1,2 and 3 SD from the mean?
1 68%
2 95%
3 99.7%
What is a Z score
Is measured in terms of standard deviations from the mean.
0 = identical to mean
Can be used in Z score table to work out %
How to calculate standard error?
What does the value of the standard error tell you?
How to calculate number needed to treat?
