Basic statistics

Question 1

What are the 4 scales data can be described?

Answer 1

Nominal - naming scale
Ordinal - ordering scale 1st, 2nd , 3rd
Interval - Scale 1,2,3,4 or 5,10,15,20
Ratio - interval scale with a fixed 0

Question 2

The shapiro-wilk test and the kolmogorov-smirov test are tools to assess what?

Answer 2

Assessing normality of data ie if normally distributed

Question 3

How to calculate median

Answer 3

(n+1)/2

Question 4

How to calculate mean

Answer 4

Total sum/n

Question 5

Is median or mean more influenced by skewed data?

Answer 5

Mean

Question 6

How do you quantify variability in a normal distribution?

Answer 6

Variance
Standard deviation
Standard error of mean
Confidence interval

Question 7

What is variance

Answer 7

The average amount by which any individual measurement differs from the mean

Question 8

What is standard deviation, why is it used?

Answer 8

Square root of the variance (in ordinal units)

As some differences will be positive and negative, differences cancel others out which is logically useless -

Question 9

What is the standard error of the mean? What does it take into consideration?

Answer 9

How close a sample mean is to the population mean

SEM: Standard deviation/sqaure root of sameple size

Question 10

What transformations of data can be used it the data is not noramally distrubuted?

Answer 10

Logarithm of the data
Square root
Squaring
reciprocal 1/x

Question 11

Binomial distribution is a scale for what kind of data?

Answer 11

Discontinous dichotomas e.g. yes/no, dead/alive

If proportion of one category is know the pther can be calcualted 1-p

Question 12

In Binomial distribution when number of observations is needed for a normal distibution

Answer 12

n>30

Question 13

Poisson disctribution is a distribution for which kind of data

Answer 13

dicrete data. arising when the number of occurances of an event per unit of time are counted

e.g. number of admission per day
It is skewed if the mean is close to 1

Question 14

The vary of propability is between what

Answer 14

0-1

Question 15

What are type one errors

Answer 15

When the hypothesis is wrongly rejected (if p<0.05, once in 20 trials)

Question 16

what are type two errors

Answer 16

When the hypothesis is wrongly not rejected

Question 17

What is power

Answer 17

Power is the probability of rejecting the null hypothesis when, in fact, it is false. (Avoiding type 2 error)
Dependant on sample size

Question 18

Which analysis can be used for testing associations between groups in non-parametric data?

Answer 18

Spearmans rho

Question 19

Which analysis can be used for testing associations between groups in normally distributed data?

Answer 19

Pearsons
Linear regression analysis
Multiple linear regression analysis

Question 20

Which analysis can be used for comparing groups in non-parametric data?

Answer 20

Sign test
Chi square
MnNemar test
Wilcoxon test
Mann Whitney U test
Kruskal-Wallit analysis

Question 21

Which analysis can be used for comparing groups in normally disributed data?

Answer 21

Student T test, paired and unparied
F test
Analysis of variance

Question 22

When can Chi squared not be used?

Answer 22

Proportion
Any expected number of observations < 5
total number of observations < 20

Question 23

What is the T-test used for?

Answer 23

Compare
- the mean of a sample with a predited value
- the means of two sample
Must be normal distribution

Question 24

In the T-test what does it mean if the confidence interval crosses 0.

Answer 24

There is no significant difference between the means of the 2 groups at the specified level of confidence

Question 25

What is persons correlations coeficient used for>

Answer 25

Measure the degree of assocaiation between 2 variable and is a measure of the scatter of the data around an underlying trend.
At least 1 set of data must be normally distrubuted

Question 26

In persons correlation coefficient, what does the values of 1, -1 and 0 mean?

Answer 26

1 - perfect positive correlation
-1 - perfection negative correlation
0 - no association

Question 27

What is sensitivity?

Answer 27

Proportion of true positives that are correctly identified

Question 28

What is specificty?

Answer 28

Proportion of true negatives that are correctly identifed

Question 29

Positive predictive value?

Answer 29

proportion of people with positive results who are correctly identified

Question 30

Negative predicitive calue

Answer 30

proportion of people with a negative result who are correctly identifed

Question 31

What is incidence?

Answer 31

The rate at which new cases of the disease occur in a population previously free of it

Question 32

What is prevalance?

Answer 32

The frequency of existing disease at a given time

Question 33

What is an odds ratio?

Answer 33

OR gives an estimate for which a confidence interval can be calculated for the association between 2 binary variables and allows for testing of other variables on thar assoication (logisitic regresstion)

Question 34

What is relative risk?

Answer 34

The relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group.
Must be selected prospectively.

Question 35

What is level 1a evidence?

Answer 35

Systematic review and meta-analysis of RCT

Question 36

What is level 1b evidence?

Answer 36

At least 1 RCT

Question 37

What is level 2a evidence?

Answer 37

At least 1 well designed control study, without randomisation

Question 38

What is level 2b evidence?

Answer 38

At least 1 other type of well designed quasi-expereimental study

Question 39

What is level 3 evidence

Answer 39

Well designed descriptive studies

Question 40

What is level 4 evidence

Answer 40

Expert committee reports/opinions and/or clinical experience of respected authorities.