Statistics

Question 1

Descriptive Statistics?

Answer 1

Descriptive statistics is what we can say about a sample by observing the sample itself. This is somewhat limited and mostly consists of summarisations of the data, e.g. like aggregates on a column in a database table.

Question 2

Inferential Statistics

Answer 2

Inferential statistics is what we can say about a population based on what we know about a sample. That means that we can infer (deduce or conclude from evidence rather than from explicit statements) about the population based on a smaller sample.

Question 3

In statistics what is ‘Probability’?

Answer 3

Probability is what we can generally say about samples from a population.

So if we know 10 % of the population are left handed, we can expect 10 % of a sample randomly taken to be left handed.

Question 4

In Probability Theory:

What does the experiment yield?

Answer 4

One possible outcome of a a sample space.

The sample space for tossing a coin is {head, tail}

Question 5

In Probability Theory

What is a ‘Sample Space S’

Answer 5

A set of possible outcomes of an experiment.

The sample space for tossing a coin is {head, tail}

Question 6

In Probability Theory

What is a ‘Event E’

Answer 6

An event is a possible outcome of an experiment, e.g. the event head when we toss a coin.

Question 7

In Probability Theory

What is a ‘Probability of Outcome P(s)’

Answer 7

The probability of an outcome is always greater than 0 and less than 1, and the sum of the probability of all possible outcomes is 1, .

Question 8

Descriptive Statistics

In Descriptive Statistics Which are the two different areas

Answer 8

Centrality and variability

Centrality: mean, median, mode

Question 9

Descriptive Statistics

What is the Mean, or average and what kind of data is it most useful for?

Answer 9

The mean / average is the sum of a value divided with the number of values.

Most useful with homogeneous data - variables of one type. categorical or binary.

Question 10

In Descriptive Statistics

What is the Median

What is the median in an evenly numbered data set?

Answer 10

The exact middle value of the data set.

If n is even, the median is the mean value of the two middle elements

Question 11

In Descriptive Statistics

What is the Mode

Answer 11

The mode is the most frequent element.

1 , 1, 2, 3, 4 = mode = 1

Question 12

Standard Deviation

Answer 12

Measure of the amount of variation on a set of values.

Low standard deviation indicates that the values are closer to the mean - the distribution is less wide

A high standard deviation indicates that the values are spread out on a wider range

Question 13

In Descriptive Statistics

Is Standard Deviation describing variability or centrality

Answer 13

Variability : Dispersion of the data

Centrality: centrality measures determine the relative significance of a node in a social network

Question 14

What is Correlation Analysis concerned with

Answer 14

Correlation analysis is concerned with relations between variables, e.g. if one goes up, what happens to the other?

Question 15

What is a Correlation Coefficient

Answer 15

A correlation coefficient is statistic measure of the degree that one variable Y is a function of another variable X.

Question 16

What does a correlation coefficient range between. and what do they mean

Answer 16

The correlation coefficient value ranges from -1 to 1, where 1 indicates perfect correlation, 0 indicates no correlation, and -1 indicates perfect negative correlation.

Question 17

Does correlation imply causation?

Answer 17

No

Question 18

Inferential Statistics

Answer 18

Used to infer about the population based on our knowledge about a sample.

Question 19

Null-Hypothesis

Answer 19

In inferential statistics, the null hypothesis is a general statement or default position that there is no relationship between two measured phenomena

An example:

Hypothesis: drinking large amounts of alcohol makes you fall over.

Null-Hypothesis: people will fall over the same amount whether they drink alcohol or not.

Question 20

What is the approach most often taken in regards to Null-Hypothesis and Hypothesis

Answer 20

We usually take the approach of rejecting the null-hypothesis; saying that the idea that there is no correlation is unlikely

• rather than confirming our hypothesis.

Question 21

What does a 95% confidence interval mean?

Answer 21

The confidence interval is the limits within which a certain percentage (say 95% or 99%) of sample means will fall.

Given observations x1-xn and 95 % confidence level, there is 95 % probability of that the mean of a sample will fall in this interval

Question 22

Significance

Answer 22

a result has statistical significance when it is very unlikely to have occurred given the null hypothesis.

Question 23

In hypothesis testing, we can make Type 1 and Type 2 errors

what is a type 1 error

Answer 23

Falsely rejecting the null-hypothesis - false positive. “You are pregnant” when he is not

Question 24

In hypothesis testing, we can make Type 1 and Type 2 errors

what is a type 2 error

Answer 24

Falsely accepting the null-hypothesis - false negative. “You are not pregnant” when she is

Question 25

What is a dependent variable

Answer 25

A variable (most often denoted Y) whose value depends on that of another variable. In an experiment it is a variable that we are not trying to manipulate.

Question 26

Independent Variable

Answer 26

A variable (often denoted X) whose variation does not depend on that of another variable. In an experiment it is the variable that we are trying to manipulate.

Question 27

In a correlation study which of the two would you apply to parametric data

Pearson’s r

Spearman’s rho

Answer 27

Pearson’s r

Question 28

In a correlation study which of the two would you apply to non-parametric data

Pearson’s r

Spearman’s rho

Answer 28

Spearman’s rho