statistics

Question 1

types of variables

Answer 1

• qualitative: either dichotomous (binary), nominal, ordinal
• quantitative: discrete or continuous

Question 2

dichotomous
qualitative variable

Answer 2

data where every observation is in one of two categories (yes/no)

Question 3

nominal
qualitative variable

Answer 3

• 3 or more categories; no inherent ordering
• ex cow breeds

Question 4

ordinal
qualitative variables

Answer 4

• categories in 3 or more categories with categories having inherent order
• ex; gum colour; normal, pale, white

Question 5

discrete data (counts)
quantitative variable

Answer 5

• can only have values as whole numbers
• ex; number of animals, heart rate, bacterial count

Question 6

continuous
quantitative variable

Answer 6

have any value within a defined range
measurement
ex body weight, blood pressure, age, hormone concentration

Question 7

descriptive statistics

Answer 7

conducted to explore patterns in data and to validate/ check the data

depend on the type of data

Question 8

mean

Answer 8

average

Question 9

median

Answer 9

line them all up and choose one in middle; not affected by a few extremes
- more accurate indicator of average

Question 10

mode

Answer 10

most commonly observed variable

Question 11

normal distribution

Answer 11

mode, median and mean are very similar

Question 12

percentile

Answer 12

• a number that indicates the percentage of values less than or equal to that number
• 50th percentile is the median
• 25% percentile means that at this data point 25% of data is less than that value

Question 13

box and whisker plot

Answer 13

the box is the 25-75% percentile (lower and upper quartile), the line in the box is the median
any dots outside of the range are outliers; either more or less than 3/2 times of lower/upper quartile

Question 14

variance and standard deviation are measures of

Answer 14

the spread of data around the mean

Question 15

variance s^2

Answer 15

the sum of the squares of the difference of each of n values from the mean, divided by degrees of freedom (n-1)

so take the mean, then each data point that point minus the mean

square root it

then divide by n-1

Question 16

standard deviation s

Answer 16

square root of variance
estimates the average variation of n the values from the mean
tells us how much variability can be expected among individuals

2/3s of the valies will be within mean +/- one standard deviation

95% of values will be within mean +/- 2 standard deviations

Question 17

standard error of the mean (SEM)

Answer 17

standard deviation/ square root of number sampled

how close sample mean is to actual mean in target population

Question 17

confidence interval (one sample only ie one type of experiment)

Answer 17

if you have a x confidence interval then in every 100 samples you collect x amount of them contain the actual mean

NOT CORRECT; if i do an experiment today there is x% chance i get the actual pop mean

Question 18

confidence interval example

Answer 18

mean +/= tSEM

t will be given to us

gives a range

Question 19

null hypothesis

Answer 19

there is NO difference between groups

Question 20

alternative hypothesis

Answer 20

hypothesis that there is a difference between groups

Question 21

want to disprove the

Answer 21

null hypothesis

Question 22

steps in hypothesis testing

Answer 22

1) from observed data, a test statistic is calculated
2) the probability (p-value) of observing a test statistic as large or larger than observed, if the null hypothesis is true is calculated
3) p value is compared to a cut off termed level of significance; should be small because we don’t want to reject null hypothesis when it is true

Question 23

p value

Answer 23

probability of observing a test statistic as large or larger than that observed, if null hypothesis is true
- if p very small, unlikely null is true; reject null hypothesis, 0.05 is alpha
- if p is large then data are consistent w the null hypothesis

Question 24

confidence (2 types of experiments)

Answer 24

- 2 experiments; if x% confidence interval for mean contains 0, then there is no difference between the groups - so if the confidence interval ie range does NOT include zero then it is unlikely there is no difference ie between groups so we reject the null hypothesis

Question 25

chi square

Answer 25

2 variables 2 outcomes yes/no dichotomous yes exposure no exposure yes injury no injury ex dogfights and injury

Question 26

one sample t test

Answer 26

- want to find mean but not really, it does find you the mean but more importantly the p value and this goes for all of them - one variable, one group - continuous, normally dist ex height in cows

Question 27

2 sample t test

Answer 27

- one variable, 2 groups - continuous, normally dist ex height in cows and humans

Question 28

paired t test

Answer 28

- one variable 2 PAIRED groups - continuous, normally dist ex blood pressure in high fibre diets vs low fibre diets

Question 29

anova analysis of variance

Answer 29

- one variable, 3 or more groups - continuous, normally dist - ex height on cows, humans and goats

Question 30

wilcoxon's signed rank test one sample

Answer 30

- one variable, one group - continuous, NOT normally dist

Question 31

wilcoxon's rank sum test

Answer 31

one variable, 2 groups continuous not normally distributed

Question 32

wilcoxon's signed rank test 2 matched pairs

Answer 32

one variable, 2 paired groups continuous, not normally dist

Question 33

kruskal wallis

Answer 33

- 1 variable, 3 or more groups continuous, not normally dist

Question 34

kaplan-meier curve with log rank

Answer 34

measures survival rate using log ranked tests