Statistics

Question 1

when do we use a spearman’s rank test?

Answer 1

used when looking for CORRELATION between two variables,
e.g. smoking and lung cancer.

Question 2

when do we use a student T-test?

Answer 2

used if looking at the difference between two MEAN VALUES.
e.g. height in males and females.

Question 3

when do we uuse a Chi2 test?

Answer 3

for when associations in CATEGORIC data is being investigated
e.g. how many men and women stopped/
did not stop at the traffic lights!

Question 4

what is a Null Hypothesis?

Answer 4

a prediction which assumes that the independent variable will not have an affect on the dependent variable

or no difference between observed and expected frequencies

Question 5

give an example of a Null hypothesis?

Answer 5

fertiliser does not affect the distribution of species

Question 6

what is an alternative/experimental hypothesis?

Answer 6

Assumes that there will be a significant difference between the observed and expected frequencies

e.g fertiliser does affect the distribution of plant species

Question 7

Chi squared test (x^2)

Question 8

what does this statistical test (chi squared) measure?

Answer 8

a statistical test to compare observed frequencies with expected frequencies, which help decide the significance of results

Question 9

when is a chi squared test used?

Answer 9

used when:
- there are two sets of frequencies (categoric data)
- the total number of observations should be 20
- the expected frequency in any category is 5 or more

Question 10

what is the equation used to calculate chi squared?

Answer 10

x^2 = Σ(O-E)^2/ E
Σ = sum of
o = observed data
E = expected data

Question 11

How can E be calculated?

Answer 11

e can be calculated as the mean of the observed data or with a contingency table

E = raw total x column total / grand total

Question 12

how to carry out a chi squared test?

Answer 12

1. justify choice of statistic
2. write a null hypothesis
3. calculate the expected value
4. calculate x^2
5. work out the degrees of freedom
6. compare the x^2 against the critical value
7. make conclusions

Question 13

how do we calculate the degrees of freedom?

Answer 13

n-1
n = number of categories

Question 14

when is chi squared considered to be significant and insignificant?

Answer 14

if the calculated value is greater than the critical value, then the null hypothesis can be rejected and there is no significant difference between the…

• if calculate value of X^2 > critical value - reject null hypothesis
• if calculated value is < critical value - accept the null hypothesis

Question 15

spearman’s rank

Question 16

what does spearman’s rank measure?

Answer 16

whether there is a statistically significant correlation between two measurements from the sample when you have 5-30 pairs of data
- measures to see if results are negative and positive

Question 17

for a test to be significant the calculated value at p<0.05 must be..?

Answer 17

more than/ Higher than the critical value

Question 18

for the test to be insignificant the calculated value must be…?

Answer 18

less than the critical value

Question 19

what is the equation for spearman’s rank?

Answer 19

1- 6 Σd^2/n(n^2-1)

Question 20

give an example of a conclusion.

Answer 20

the calculated value of Rs =x at p<0.05 is less than the critical value = 4x. so we must accept the null hypothesis. there is statitstically no correlation between X and y. The correlations are due to chance

Question 21

students t-test