Statistics

Question 1

What are the different types of quantitative data?

Answer 1

Discrete: counted (number of cigarettes smoked per day)
Continuous: measured (e.g. height)

Question 2

What are the different types of qualitative data?

Answer 2

Nominal: naming (calorie-controlled/Atkin’s/high-fibre diets)
Ordinal: in a meaningful order (e.g. obese/normal/under, agree/neither/disagree)
Binary: only two values (e.g. yes/no, male/female, alive/dead)

Question 3

What is mean, median and mode?

When is it appropriate to use each?

Answer 3

Mean: the mean is the sum of data values divided by number of data values (use for symmetric data)
Median: the median is the middle value when the data is ranked (in numerical order) (use for skewed data)
Mode: the mode is the most frequently occurring value in a data set

In general, the mean is used as the measure of centre for quantitative data, unless the distribution of the data is skewed or there are extreme values. In this case, the median would be quoted.
The mode is the measure of centre for qualitative data.

Question 4

What is variance and standard deviation?

Answer 4

The variance and standard deviation (SD) are measures of the spread of the data about the mean.
The variance is the average of the squared deviations for the mean
The standard deviation is the square root of the variance (measure of choice for continuous data and most discrete observations; interquartile-range useful if there are outlying observations).
95% of data falls in mean +/- 1.96 x sigma

Question 5

What are the normal distribution, binomial distribution and poisson distribution models of data?

Answer 5

Normal distribution: continuous variables (e.g. length, height and weight)
Binomial distribution: binary data (e.g. alive/dead, male/female)
Poisson distribution: for events occurring at intervals of time or space aka counts per bin (e.g. deaths per year)