Statistical Testing

Question 1

What does standard deviation show?

Answer 1

How much variation there is between the data and the mean value
How consistent the data is, unlike range which only shows biggest and smallest

Question 2

What does each part of the standard deviation equation stand for?

Answer 2

s is standard deviation
x refers to each measured value in data set
x¯ (line is normally over the x) refers to arithmetic mean
n is number of values measured
∑ = the sum of, means add together the values indicated to right of symbol

Question 3

What is an unpaired t-test?

Answer 3

Compares the means from different individuals (eg treated and untreated)
Looks to see if there is a significant difference between two sets of data, comparing means to see if different.
Tells if difference is random, due to chance or not
Gives probability

Question 4

Example of null hypothesis compared to hypothesis

Answer 4

Hypothesis: chickens fed maize supplemented by lipid produce more male offspring than those fed maize alone
Null Hypothesis: There is no difference between the number of male and female offspring of chickens fed maize supplemented by lipid and those fed maize alone

Question 5

What does each part of the unpaired test equation mean

Answer 5

x1¯ (line is normally over the x1) is the mean of sample 1
s1 is the standard deviation of sample 1
n1 is number of individuals in sample 1
x2¯ (line is normally over the x2) is the mean of sample 2
s2 is the standard deviation of sample 2
n2 is the number of individuals in sample 2

Question 6

When do you accept or reject the null hypothsis

Answer 6

when t>= critical value, reject the null hypothesis as significant different present
when t < critical value, accept the null hypothesis as not a significant difference

Question 7

What is a critical value?

Answer 7

The value corresponding to a given significant level
Cut off value determines boundary, leads to decision not to reject null hypothesis

Question 8

What is a degree of freedom, and how is it calculated?

Answer 8

The number of independent pieces of information used to calculate a statistic
(n1+n2) - 2

Question 9

What is probability level?

Answer 9

Probability of rejecting null hypothesis when it is true
Normal standard is P=0.05 (5% uncertainty/risk), as still 95% confident that choice is right
In certain trials, P=0.01, as 1% risk of being wrong but 99% certain of correct result
Lower P in trials such as drugs/medical trials