Lecture 3-Summarising data

Question 1

what is a variable?

Answer 1

subject’s characteristics taking any number of a set of values

Question 2

what is a qualitative variable?

Answer 2

(catergorical)
falls into a specific catergory
e.g. Sex, hair colour, ethnic group

Question 3

what is a quantitative variable?

Answer 3

Continuous or discrete

1. Continuous
   - variables can take any number of values –> height / weight
2. discrete
   - variables that can only take integer measuremnets
   - number of children / number of pre-existing diseases

Question 4

what are the three scales of measurement

Answer 4

1. interval scale –> height / BMI / BP
2. Nominal catergory –> sex / hair colour
3. ordinal catergory –>QOL / hospital performance ranking

Question 5

what does the frequency distribution show?

Answer 5

shows how often different values of a variable occur in the dataset, usually described as a graph or table

Question 6

what is the frequency distribution graph for nominal / ordinal data?

Answer 6

Bar chart

-frequency on y-axis and values on the x-axis

Question 7

how can frequency distribution be shown on interval scale variables?

Answer 7

Histogram
-where the class intervals are on an axis and rectangles with heights or areas proportional to the frequencies are stacked on them

Question 8

what is relative frequecy?

Answer 8

frequency expressed as percentage of the total frequency

Question 9

What is the mean?

Answer 9

centre value of the sample

-sum of all the values divided by the number of values

Question 10

what is the median?

Answer 10

Middle value of the data

-resistant measure of data’s center

Question 11

what is measure of dispersion?

Answer 11

the value each data piece has from the mean

Question 12

what is variance?

Answer 12

The variance of the sample is the mean of the squared deviations of the values from their mean

Question 13

what is standard deviation

Answer 13

square root of the variance

Question 14

what is the range?

Answer 14

Highest number - lowest number

prone to outliers

Question 15

what is the IQR

Answer 15

UQ - LQ

Question 16

what is a positive skew?

Answer 16

Skew to the right

but the graph is towards the left

Question 17

what is a negative skew?

Answer 17

Skew to the left

graph is towards the right

Question 18

When would you see a uniform symmetrical histogram?

Answer 18

throwing a dice

Question 19

What is included in the five number summary boxplot?

Answer 19

1. Min
2. Q1
3. Median
4. Q3
5. Max

Question 20

How to deal with outliers?

Answer 20

Check for obvious mistakes.
When/who recorded the data.
How are the results affected?
Can the results be analysed a different way?
Do not simply discard!

Question 21

What do outliers do to the data?

Answer 21

affect mean and standard deviation

do 5 calculations with the outliers present

Question 22

what is preferred when data is heavily skewed?

Answer 22

IQR and median