Statistics - Location and spread Flashcards Preview

A Level - Maths > Statistics - Location and spread > Flashcards

Flashcards in Statistics - Location and spread Deck (31):
1

What is a measure of location?

Single value which describes a position in a data set

2

What is a measure of central tendency?

Single value that describes the centre of the data

3

What is the mean?

Sum of data values / number of data values

4

What is the median?

The middle value when the data values are put in order

5

What is mode?

The value or class that occurs most often

6

When should median be used?

Used when there are extreme values
Quantitative data

7

When should mean be used?

Quantitative to represent all data
But affected by extremes

8

When should mode be used?

Qualitative or quantitative
Either one or two modes
Not very informative if each value occurs once

9

How can the mean of data in a frequency table be calculated?

Mean = Sum of products of data and their frequencies / sum of the frequencies

10

What is the lower quartile?

Q1
One-quarter of the way through the data set

11

What is the upper quartile?

Q3
Three-quarters of the way through the data set

12

How is data split if there is a 85th percentile?

85% of data is less than 85th
15% of data is more than 85th

13

How can you calculate the lower quartile for discrete data?

n/4
If whole number, Q1 is halfway between this point and the one above
If not whole number, round UP and pick this data point

14

How can you calculate the upper quartile for discrete data?

3n/4
If whole number, Q3 is halfway between this point and the one above
If not whole number, round UP and pick this data point

15

How can you calculate Q1-3 for cumulative frequency table?

Q1 = n/4 th data set
Q2 = n/2 th data set
Q3 = 3n/4 th data set
NO ROUNDING

16

Define percentile

The value below which a percentage of data falls

17

What is interpolation?

Technique to estimate the Q1-3 and percentiles
This assumes the data values are evenly distributed

18

What is the equation for linear interpolation?

(Quartile - freq. below / freq of group) x width + lower class boundary

19

What is the range?

Difference between largest and smallest values in the data set

20

What is the interquartile range IQR?

Difference between upper and lower quartile
Q3 - Q1

21

Why is IQR used?

It does not include extreme values
Only considers spread of middle 50% of the data

22

What is the inter-percentile range?

Difference between the values for two given percentiles

23

What is variance a measure of?

The spread of a data

24

What is the equation for variance?

(Sum of x^2/n) - (Sum of x/n)^2

25

What is the equation for standard deviation?

Sqrt of (Sum of x^2/n) - (Sum of x/n)^2
Square root of variance

26

How is variance/standard dev. different for grouped data in a frequency table?

x is always times by its frequency

27

What is coding?

A technique to simplify statistical calculations
Allows easier data to work with

28

What is the equation for coding data?

y = (x-a)/b

29

What is the equation for the mean of coded data?

mean of y = (mean of x - a)/b

30

What is the standard dev. of coded data?

Coded standard dev. = standard dev. / b

31

What affects measures of location and spread in coding?

Add/subtract affects mean not spread
All affected by stretch x or /