Statistics

Question 1

What’s a census?

Answer 1

Measurement of every member of a population

Question 2

What are the benefits of a census?

Answer 2

Accurate results

Question 3

What are the drawbacks of a census?

Answer 3

They are expensive
May destroy the products being tested ( may have to break the thing being tested)

Question 4

What are sampling units?

Answer 4

Individuals of the population

Question 5

What is the sampling frame?

Answer 5

A list of all the sampling units

Question 6

What is random sampling?

Answer 6

Sampling with each unit having the same chance of being selected. (use of a random number generator or lottery sampling)

Question 7

Advantages of random sampling?

Answer 7

Bias free

Question 8

-ves if random sampling??

Answer 8

Requires a sampling frame

Question 9

What is systematic sampling?

Answer 9

Taking a kth unit, 1st –> 11th –> 21st ect

Question 10

+ves of systematic sampling?

Answer 10

Quick to use

Question 11

-ves of systematic sampling?

Answer 11

Requires a sampling frame

Question 12

What’s stratified sampling?

Answer 12

The sample represents the groups (strata) of the population
(sample/population) *strata
then pick randomly

Question 13

+ves of stratified sampling?

Answer 13

Reflects the population

Question 14

-ves of stratified sampling?

Answer 14

Data must be classified into strata

Question 15

Quota sampling?

Answer 15

The same a stratified sampling but with interviewers

Question 16

+ves of quota sampling?

Answer 16

no sampling frame

Question 17

-ves of quota sampling?

Answer 17

not random/ bias

Question 18

Opportunity sampling?

Answer 18

Quota filled with people that are available at the time

Question 19

+ves of opportunity sampling?

Answer 19

Cheap and easy

Question 20

-ves of opportunity sampling?

Answer 20

unlikely to be representative

Question 21

mean (x̄)?

Answer 21

Σx / n or Σf(x) / Σf

Question 22

Quartiles of Listed Data?

Answer 22

Q1 = n/4 Q2 = n/2 Q3 =3n/4

Question 23

Quartiles of listed data when decimal and whole?

Answer 23

If you get a decimal, round up
If you get a whole number find the midpoint

Question 24

How to interpolate?

Answer 24

Find the true class limits e.g
10-12 –> 9.5=< x <12.5

lower bound of true class limit + class width*(number into class/( total number in the class))

Question 25

What is the benefit of using the IQR?

Answer 25

Ignores extremes

Question 26

Variance?

Answer 26

(Σx^2)/n -(x̄)^2
mean of the squares - square of the mean

Question 27

Coding?

Answer 27

y= ax + b the ȳ =ax̄=b
σy = aσx

Question 28

What is frequency density?

Answer 28

Frequency / class width

Question 29

Formula for the area of the histogram?

Answer 29

area = frequency x k

Question 30

What is PMCC? (r)

Answer 30

only takes values between -1 and 1
Measures the strength of correlation

Question 31

What is interpolation?

Answer 31

Estimation within the date range

Question 32

What is extrapolation?

Answer 32

estimation outside the data range

Question 33

P(B|A)

Answer 33

P(BnA)/P(A)

Question 34

P(A u B)

Answer 34

P(A) + P(B) - P(AnB)

Question 35

What is a discrete uniform distribution?

Answer 35

Probabilites of all outcomes are equal

Question 36

What is a binomial distribution?

Answer 36

X ~ B(n, p)

Question 37

When to use a binomial distribution?

Answer 37

Fixed number of trials
Fixed p of success
Independent trials
Either success or failure

Question 38

Standard normal dist?

Answer 38

Z ~ N(0,1^2)
Z =y-μ/σ

Question 39

Conditions of represent a Binonial as normal?

Answer 39

n is large
p is about 0.5
μ = np
σ^2 = np(1-p)

Question 40

What must be done after approximating the normal?

Answer 40

Continuity correction

Question 41

What is the actual significance level of a test?

Answer 41

When you reject Ho when it is true

Question 42

Sxx to variance?

Answer 42

Sxx / n