Statistics

Question 1

What are the two main types of data

Answer 1

quantitative

qualitative

Question 2

What is ordinal data

Answer 2

the data can be given a meaningful order

Question 3

What is nominal data

Answer 3

there is no relationship that is meaningful in terms of order of the categories ie. it is just name e.g. atkins diet and paleo diet

Question 4

What is binomial data

Answer 4

there are only two options e.g. yes or no

Question 5

What is a random sample

Answer 5

one in which each member of the population has an equally likely non zero chance of being included

Question 6

what is a stratified sample

Answer 6

one in which certain categories of the population must be represented e.g. if we know the library is 50 percent history books, 30 percent science and 20 percent others. in a sample of 20 we must select 10 history books, 6 science and 4 others.

Question 7

what is a convienience sample

Answer 7

one that is not chosen randomly but is all that is available eg. all patients at an outpatient dermatology clinic

Question 8

when would you use a bar or pie chart

Answer 8

categorical data

Question 9

when would you use histograms, stem and leaf plots and box and whisker plots

Answer 9

to visualise continuous data

Question 10

what does a scatter plot show

Answer 10

the relationship between two variable and how one changes in relation to the other

Question 11

when would you use the mean and when would you use the median to describe the centrality of data

Answer 11

mean - normal distriuted not skewed data
media- if data is more skewed or significant outlier
mode- used for qualitative data

Question 12

what do you do differently when calculating the sample variance/sd as opposed to the population

Answer 12

use n-1 as the denominator instead of n

Question 13

what does the standard deviation show

Answer 13

the spread of the data

Question 14

what does positively skewed mean

Answer 14

that more of the values are clusted towards the bottome of the scale - such as alcohol intake

Question 15

what is negatively skewed

Answer 15

most of the values are clustered at the higher range of the scale - rare in clinical data

Question 16

what is the coefficient of skewness

Answer 16

a value which shows how skewed the data is - the closes to 0 the more symmetrical the data

Question 17

what does a value of 0 for the kurtosis mean

Answer 17

indicates that the shape of the data is close to the normal distribution

Question 18

what is inference

Answer 18

making predictions about a population based on the data collected from a smaller sample or series of smaller samples

Question 19

what are the characteristics of a normal distribution

Answer 19

continuous
symmetrical
bell shaped curve
mean, median and mode are equal
single central peak
values between -infinity and +infinity

Question 20

what is the binomial distribution

Answer 20

for binary data e.g. dead/alive, male/female

Question 21

what is the poisson distribution

Answer 21

for events which occur at random intervals of time or space e.g. deaths per year.
rare events

Question 22

what is the mean and sd of a standard normal distributions

Answer 22

mean = 0
sd = 1
we write z~ N (0,1)

Question 23

where would you expect 95 percent of values to like in normally distributed data

Answer 23

mean +/- 1.96 x SD

Question 24

how can you assess the normality of data

Answer 24

Informal review of properties of normal distribution
Inspection of a normal plot
Shapiro- Wilk test

Question 25

Name ways in which you can transform data to make it plausibly normal and when you would use each one

Answer 25

``` Logarithmic - fairly skewed data in which the variances are proportional to the mean Square root - countrs Reciprocal - highly skewed data Cube- volumes Logit - proportions ```

Question 26

what is the variance of expected number of events

Answer 26

nxpx (1-p)

Question 27

when can the binomial distribution be approximated to normal

Answer 27

if np > 5 and n(1-p) >5

Question 28

what is the standard error

Answer 28

the standard deviation of the mean

Question 29

When can you make inferences about sample means based on the normal distrubution

Answer 29

1. sample is selected from normal population with known SD or the sample size is large 2 observations in the sample are independent

Question 30

when should the hypothesis be defined

Answer 30

before data is collected

Question 31

what is a type 1 error

Answer 31

rejecting a true null hypothesis

Question 32

what is a type 2 error

Answer 32

accepting a false null hypothesis

Question 33

What does the level of significance of a test mean

Answer 33

the probability of making a type one error

Question 34

what is the generally accepted risk of making a type 2 error

Answer 34

20 percent

Question 35

if your significant level is 5 percent what is you confidence level

Answer 35

95 percent

Question 36

When is students t distribution used

Answer 36

When the population standard deviation is not known - for normally distributed data

Question 37

What is the degrees of freedom in t distribution

Answer 37

one less than the sample size

Question 38

What is the difference between and independent and dependent sample

Answer 38

``` independent = different people dependant= same people ``` however if samples from two different groups are match e.g. for age and gender the sample could then be viewed as dependant

Question 39

What are the steps that can be done to compare the means of two samples with incomparable sample variances

Answer 39

1. investigate the relationship between the means and variances 2. use Welch's modified t test 3. do non parametric tests 4. do not process with the test of the means

Question 40

what does it mean if the F statistic is not significant

Answer 40

the variances of the two samples are comparable

Question 41

when can you use the normal approximation for a binomial trial

Answer 41

if both np and n(1-p) are greater than 5

Question 42

what is regression

Answer 42

provides information about the nature of the relationship e.g linear

Question 43

what is correlation

Answer 43

asses the extent of the associations between two variables

Question 44

when is a logistic regression used

Answer 44

when one variable is categorical

Question 45

how do we measure the linear relationship between two variables

Answer 45

correlation coefficient

Question 46

what is the most commonly used measure of correlation

Answer 46

Pearson's product moment correlation coefficient (r)

Question 47

What are the three main points to remember about r

Answer 47

r value increases with sample size at least one value should be normally distributed random sample the pairs of variables are independent correlation can be mathematically significant but not clinically significant

Question 48

what is r squared

Answer 48

measure of the proportion of the variation in the dependent variable which is attributable to its linear relationship with the independent variable

Question 49

what assumptions are made when using regression methods

Answer 49

correlation between x and y significant for each value of the x variable, the values of the y variable have a normal distribution variances of these normal distributions are equal

Question 50

up to what sample size can the Shapiro wilk test provide a test for normality

Answer 50

up to 2000

Question 51

what do the results of the Shapiro wilk test mean

Answer 51

closer to 1 = the more normal the data is

Question 52

what is a cohort study

Answer 52

a group of disease free subjects are followed up over time

Question 53

what is a case control study

Answer 53

retrospective study of people with a disease. compares factors they have been expose to with controls

Question 54

advantages and disadvantages of a cohort study

Answer 54

less likely to be biased expensive not suitable for rare diseases

Question 55

what are the advantages/disadvantages of a case control study

Answer 55

cheap and easy to do | could be biased

Question 56

what factors influence the sample size needed in a study

Answer 56

``` significance level power of the test size of effect to be identified standard deviation of the measurements- greater the SD the greater the sample size needed study design practical issues ```

Question 57

when are parametric tests used

Answer 57

for normally distributed data

Question 58

when are non parametric tests used and name examples

Answer 58

for skewed i.e. not normally distributed data | e.g. chi squared, Wilcoxon, sign

Question 59

what is another name for non parametric tests

Answer 59

distribution free

Question 60

what is the disadvantage of non parametric techniques

Answer 60

they are less powerful than parametric techniques as such all efforts to transform data to approximate normal distribution should be done first

Question 61

what do non parametric techniques use as a representative of centre

Answer 61

the median

Question 62

when should a large sample Wilcoxon statistic which approximated the normal be used

Answer 62

when n>25