Data, Variables, Tables

Question 1

What is a variable?

Answer 1

Any characteristic of an individual that can be measured or reported like age, sex or BMI

Question 2

Variables can be classified as either numerical or categorical. Describe numerical variables

Answer 2

1. Numerical variables:
   → quantitative
   → individuals are measured or counted
   → can be continuous (any value in a range) or discrete (certain values)
   → numerical variables are measured mostly on interval scales (the interval between points on the scale has precise numerical meaning)

Question 3

Variables can be classified as either numerical or categorical. Describe categorical variables

Answer 3

2. Categorial variables:
   → qualitative
   → individuals classified into groups
   → 3 types of categorical variables: binary, nominal, and ordinal
   • Binary- can only take 2 values -mainly yes/no
   • Nominal- more than 2 categories but no natural order
   • Ordinal- more than 2 categories with a natural order
   But, ordinal data doesn’t tell the differences between categories e.g. what is the highest level of education completed?..high school..bachelors.. etc

Question 4

Draw a flow diagram to explain the difference between the types of variables

Answer 4

Question 5

What are the methods of summarising each data type?

Answer 5

For numerical:
- Measures of central tendency (mean, median) if data is not normally distributed. Measures of spread if the data is normally distributed. (standard deviation, range)
For categorical:
- Frequencies
- Proportions
- Percentages
- Use tables & charts to do this

Question 6

What is the difference between mean and median?

Answer 6

Mean is simply the average of all the values. Sum up all individual values & divide by number of ppl.

Median is the value such that 50% of data points lie at or above the median & 50% at or below it
Order data from low to high, take the middle value. If there is an even number = take average of central 2 values

Question 7

When should we use mean vs median?

Answer 7

MEAN is good measure of the centre of a symmetrical distribution
– Much more useful in practice
– But over influenced by extreme values

MEDIAN is better for skewed distributions because it is only slightly affected by extreme values (no matter how big they are)

Question 8

Describe what distribution curves show

Answer 8

Question 9

How do you estimate a 95% reference range?

Answer 9

We are interested in the range of values from (apparently) healthy individuals for a particular measurement. Range may vary by sub-groups (age, gender)

Mean ± 1.96 x SD
→ 95% of the data lies between these limits IF data are normally distributed