Interpreting Data

Question 1

what are the two types of data

Answer 1

• Qualitative

- Quantitative

Question 2

describe what qualitative data splits into

Answer 2

Qualitative data splits into nominal (unordered) and ordinal (ordered e.g. short medium tall)
- Nominal this then split into binary (yes or not questions) and categorical (e.g. different colours)

Question 3

what is the name of the data that is unordered in qualitative data

Answer 3

nominal

Question 4

What is the name of the data that is ordered in qualitative data

Answer 4

ordinal

Question 5

What is quantitative data split into

Answer 5

• discrete ( 10 graduates - whole number)

- Continuous ( length in cm - doesn’t have to be a whole number)

Question 6

What are two other ways in which you can summarise data

Answer 6

Measure of location

measure of spread

Question 7

What makes up the measure of location

Answer 7

• Median = Middle value when the values are ordered from smallest to largest
• Mode = the most common value
• Mean = average = sum of all of the values divided by the number of values

Question 8

What makes up the measure of spread

Answer 8

• standard deviation

- interquartile range

Question 9

When is it better to use the median over the mean

Answer 9

• Better to use median in order to avoid the influence of outliers (large or very small numbers that can be incorrect in the data)
• Also use it when the data is skewed

Question 10

When is it better to use the interquartile range over standard deviation

Answer 10

• Use the interquartile range in order to avoid the influence of outliers
• also used when the data is skewed

Question 11

How do you work out the interquartile range

Answer 11

range is between the 25th and 75th percentile

e.g. 1,  2,  3,  4,  5,  6,  7
Interquartile range (IQR) = 2 to 6

Question 12

How do you work out the standard deviation

Answer 12

• work out the mean
• then from each result subtract the mean and square the result
• then divide by N (number of participants)
• then square root it

Question 13

Why is AFP levels important

Answer 13

If you aren’t pregnant, an AFP test can help to diagnose and monitor certain liver conditions, such as liver cancer, cirrhosis, and hepatitis.

Question 14

What is an antenatal thyroid screening test

Answer 14

• this is a test that screens thyroid and therefore is able to prevent defects in the babies

Question 15

What is another name for the Gaussian distribution

Answer 15

normal distribution

Question 16

what two things is the normal distribution determined by

Answer 16

• Normal distribution is determined only by the mean and standard deviation

Question 17

What happens if you change the mean to the normal distribution curve

Answer 17

• the curve moves left and right but stays the same height - if it decreases it moves to the left whereas if it increases it moves to the right

Question 18

What happens if you change the standard deviation to the normal distribution curve

Answer 18

• the height of the curve changes but the area under the curve remains the same
• as the number increases the curve becomes more flattened

Question 19

What are the characteristics of Gaussian distribution

Answer 19

• A constant proportion of values will lie within any specified number of Standard Deviations above or below the mean

Question 20

What standard deviation correlates to the

• 99% range
• 95% range
• 90% range

Answer 20

99% range (0.5th to 99.5th centile) = mean ± 2.58 SDs
95% range (2.5th to 97.5th centile) = mean ± 1.96 SDs
90% range (5th to 95th centile) = mean ± 1.64 SDs

Question 21

How do you calculate the 95% percentile

Answer 21

Mean +- 1.96 x standard deviation

Question 22

what is statstics used for

Answer 22

• Statics used for our sample to tell us something about the population

Question 23

What does the population contain

Answer 23

Population contains the true mean

Question 24

What happens if the sample size is large enough

Answer 24

If the sample size isn’t too small then the distribution of the sample mean will be Gaussian

Question 25

what is the standard deviation of the sample size

Answer 25

the standard error of the mean

Question 26

What is standard error

Answer 26

The standard error is a measure of the statistical accuracy of an estimate

Question 27

What is the standard error of the mean

Answer 27

- The standard error of the mean is the standard deviation of the distribution of all possible sample means

Question 28

How do you work out the standard error of the mean

Answer 28

= Standard deviation/ square root of sample size

Question 29

How do you work out a confidence interval

Answer 29

95% confidence interval = sample mean +- 1.96 x standard error

Question 30

Define the confidence interval

Answer 30

a range of values so defined that there is a specified probability that the value of a parameter lies within it.

Question 31

How would you right about the confidence internval in an exmaple

Answer 31

IN THE POPULATION we are 95% sure that the mean weight could be as low as 75kg or as high as 81kg

Question 32

When do we use standard deviation

Answer 32

- use standard deviation for ranges (for individual values)

Question 33

When do we use standard errors

Answer 33

- use standard error for confidence intervals (for means)

Question 34

What happens as the sample size increases

Answer 34

- As the sample size increases the 95% confidence interval gets narrower, this is because the standard errors get smaller - Increase in accuracy therefore you can be more confident in the accuracy of our estimate

Question 35

Describe the different types of correlation and there numbers

Answer 35

- R = 0 - no correlation - R = 1 – perfect positive correlation - R = -1 – perfect negative correlation

Question 36

What is the correlation coefficient

Answer 36

- R = 0 - no correlation - R = 1 – perfect positive correlation - R = -1 – perfect negative correlation

Question 37

define the correlation coefficient

Answer 37

a number between +1 and −1 calculated so as to represent the linear interdependence of two variables or sets of data.

Question 38

How do you work out linear regression

Answer 38

``` Y = a + bx Y = outcome (deponent variable) X = predictor (independent variable) a = the point at the line crosses the X axis ```

Question 39

What is the dependent variable

Answer 39

a variable (often denoted by y ) whose value depends on that of another

Question 40

What is the independent variable

Answer 40

a variable (often denoted by x ) whose variation does not depend on that of another

Question 41

Why do you want to know if the result is statistically significant

Answer 41

* An observed sample difference between groups might be due to chance * We want to know whether a result is statistically significant i.e. unlikely to be due to chance

Question 42

How do you determine if the result is statistically significant

Answer 42

• To determine whether an observed difference was due to chance we look at confidence intervals and p-values

Question 43

How do you work out the confidence intervals between two groups

Answer 43

95% CI = mean difference ± 1.96 × SE of mean difference

Question 44

What is a P value

Answer 44

a p-value for a result is the probability of observing a result as or more extreme than the sample result if the underlying assumption in the population is true

Question 45

When is a confidence interval result significant

Answer 45

- Doesn’t cross 0 therefore there is a difference in the population - If the confidence interval crossed 0 then there might not be a difference

Question 46

When is a P value statistically significant

Answer 46

when the value calculated is less than 0.05

Question 47

When can P values be calculated

Answer 47

When there is a comparison - 2 means – are they different i.e. is their difference different from 0? - Association – are the observed results different from those expected - Regression – is the slope different from 0?

Question 48

Where does the P value come from

Answer 48

The p-value comes from a chi-squared test. P=0.002, so we can be confident there is an association

Question 49

What is the chi squared test used for

Answer 49

categorical variables

Question 50

What is a T test used for

Answer 50

Comparing continuous variables