Lecture 4 - Distributions, Introduction to Experimental Design & Statistics

Question 1

assumption of distribution in the mean:

Answer 1

normal

Question 2

assumption of distribution in the median:

Answer 2

none

Question 3

shape of normal distribution curve:

Answer 3

bell-shaped, asymptotic at the extremes, symmetrical at the mean [no skew], mean = median = mode

Question 4

area under the normal distribution curve is:

Answer 4

directly proportional to the relative frequency of observations and their probability: p

Question 5

relationship between the mean and standard deviation in normal distribution:

Answer 5

in a normal distribution, mean and standard deviation are independent of each other: infinitely many possible combinations of mean and standard deviation and hence infinite number of normal distributions possible

Question 6

standard normal distribution (z-distribution):

Answer 6

• developed to compare all normal distributions
• a normal distribution with a mean of 0 and a standard deviation of 1
• area under curve is 1

Question 7

poisson distribution:

Answer 7

often discrete, count data [often plummeting at the bottom]

Question 8

binomial distribution:

Answer 8

proportions, binary variables [e.g. ‘heads & tails’]

Question 9

statistical hypothesis:

Answer 9

statement about the world that can be falsified

Question 10

null hypothesis (H0):

Answer 10

no difference, no relationship, no effect, no signal

Question 11

alternative hypothesis (H1):

Answer 11

[normally our research hypothesis] - signal

Question 12

Y variable & X variable:

Answer 12

Y - response (subject to hypothesis): binary, proportion, continuous, discrete

X - explanatory (object of hypothesis): binary, proportion, continuous, discrete, categorical

Question 13

what axis/variable is subject of hypothesis?

Answer 13

the Y variable

Question 14

basis of experimental design:

Answer 14

manipulation of the explanatory X variable

measure change in the response Y variable

can test for causation

Question 15

how can we increase the power of an experiment?

Answer 15

through decreasing the noise - increasing sample size and randomising

Question 16

statistical tests have:

Answer 16

• A test statistic (e.g. t, F, Chi²) with value
• Degrees of freedom
• P-value, p-value

Question 17

degrees of freedom:

Answer 17

number of independent observations minus number of parameters we estimated from the data

Question 18

figure legends:

Answer 18

given under the figure and should be informative; i.e. reader needs to understand the figure without reading the main text. All abbreviations etc. need to be explained.Table captions are given before the table

Question 19

mean and SD of standard normal distribution (z-distribution):

Answer 19

standard normal distribution (z-distribution) has a mean of 0 and a standard deviation of 1

Question 20

we can compare all normal distributions to the standard normal distribution by:

Answer 20

• converting our y into a number of standard deviations from the mean and finding the probability with which this value lies in a range

Question 21

research processes include:

Answer 21

formulation of hypotheses, planning of experiment,
summarising & analysing data (descriptive & inferential statistics), interpretation of results

Question 22

large part of the research process involves:

Answer 22

hypothesis testing

Question 23

Statistical (null) hypothesis:

Answer 23

statement about the world that can be falsified; no signal

Question 24

Alternative hypothesis:

Answer 24

signal (often our research hypothesis)

Question 25

what experiments can and can’t test causation?

Answer 25

Correlative, descriptive studies cannot test causation; experiments that manipulate the explanatory variable can test causation

Question 26

statistical tests provide:

Answer 26

a test statistic with value, degrees of freedom and a p-value

Question 27

p-value:

Answer 27

probability of getting a test statistic as large as yours (or higher) if the null hypothesis is true; probability that a null hypothesis (H0) is true

Question 28

how do you calculate the degrees of freedom?

Answer 28

number of independent observations - number of parameters we estimated from the data

Question 29

figure legends are given under the inure and should be informative:

Answer 29

reader needs to understand the figure without reading the main text

all abbreviations etc. need to be explained, table captions are given before the table

results and methods are written in past tense, give direction of effect, test statistics are given in brackets