Unit 4: descriptive statistics

Question 1

what are the 4 types of data sets

Answer 1

nominal
ordinal
interval
ratio

Question 2

how do you know if a statistic is nominal?

Answer 2

has names, such as:
in land use - commercial, residential, agricultural etc
rock types - sedimentary, metamorphic
or just straight up names like locations

Question 3

how do you know if a statistic is ordinal?

Answer 3

data can be placed in descending or ascending order such as settlement type: city, town, village, swamp

Question 4

how do you know if a statistic is interval?

Answer 4

refers to real numbers with no true zero - only asked about temp

Question 5

how do you know if a statistic is ratio?

Answer 5

numbers with no real zero - rainfall in mm etc
most number data will be in this category

Question 6

how do you calculate the mean?

Answer 6

the average - all the numbers added together then divide by the values

Question 7

how do you calculate the median?

Answer 7

middle value - all the numbers in a line and find the middle

Question 8

how do you calculate the mode?

Answer 8

the most common number - can be two of them

Question 9

how do you calculate the range?

Answer 9

difference between the max and min number - for example if the biggest number was 90 and the min was 10 then the range is 80

Question 10

What is the methodology for spearmen’s rank correlation coefficient by hand

Answer 10

Not reliable as <10 pairs is too little and >30 is too much
1) construct table and write variables (x2)
2) draw scatter graph for this data and establish null hypothesis
3) rank data from lowest to highest (x2)
4) calc diff between numbers and put into colum
5) calc *2
6) choose between tied and non tied formula
7) interpret results

Question 11

What is the methodology for persons product moment correlation coefficient

Answer 11

1) create scatter graph and null hypothesis for data
2) test strength with formula
Further technique used to test significance of relationship
3) work out degrees of freedom

Question 12

What is the purpose of SRCC and PPMC

Question 13

What are the positives and negatives for PPMC

Answer 13

Assumes linear relationship between variable even when not existing
Tedious to calc
Effected by extreme values - skews data
High degree of correlation doesn’t mean close to casual relationship between variables - can confuse viewer

Question 14

What is the purpose of central tendency

Answer 14

Central tendency tells you the middle point in a set of data, done through mode, median and mean - used on already collected data

Question 15

What are the pros and cons of central tendency

Question 16

What is the purpose of dispersion

Answer 16

Important for describing the spread of data around a central value as two sets of data can have same modes and medians yet diff spread
Done with SIQR, IQR, range and standard deviation

Question 17

What are the pros and cons of dispersion

Answer 17

Pros: in graphs, normal distributions and anomalies are easily identifiable visually. Data is easy to calc as either whole numbers or at two decimal places

Neg: very sensitive to outliers, can skew data and null hypothesis. Difficult to produce. Overlapping in data can be confusing to read