Statistics

Question 1

When would Chi- squared be used?

Answer 1

• Concerned with frequencies

e. g experiment involves collecting data about the no. of individuals in certain categories

Question 2

What does the t-test tell us?

Answer 2

If there is a statistically significant difference between the mean values of 2 data sets when the data is normally distributed (bell-curve)

Question 3

When would spearman’s rank be used?

Answer 3

Looking for a correlation between measurements of a different a variable from the same sample

Question 4

What is a null hypothesis?

Answer 4

States that there is no significant difference/no correlation

Question 5

What is a p value?

Answer 5

Calculated result of statistical test

- If it’s higher than the critical value (at 0.05) then your results are not significant as they are due to chance

Question 6

How do you calculate degrees of freedom?

Answer 6

no. of possible outcomes (n) - 1

e. g rolling a die: 6 possible outcomes = 5 degrees of freedom

Question 7

What type of experiments is the chi-squared test normally used for?

Answer 7

• Genetic cross experiments
• Choice chamber behavioural studies
• Counts of the no. of individuals of different species

Question 8

What is the null hypothesis for chi-squared?

Answer 8

States that there will be no significant difference between the observed results + expected results

Question 9

In the chi-squared test, how do you calculate the expected frequencies?

Answer 9

• If the chance of every outcome is equal:
  no. of trails/no. of outcomes
  e. g rolling a dice 60 times: 60 rolls/6 sides = 10
• If the chance is unequal (e.g genetics):
  / no. of trails in the same ratio as expected

Question 10

What does O stand for in the chi-squared equation?

Answer 10

Observed frequencies

Question 11

What does E stand for in the chi-squared equation?

Answer 11

Expected frequencies

Question 12

How do you interpret the results of the chi-squared test?

Answer 12

If the calculated value is LOWER than the critical value, we accept the null hypothesis

If the calculated value is GREATER than the critical value, we reject the null hypothesis

Question 13

What is the t-value?

Answer 13

Measures the size of the difference in mean values relative to the variation of your sample data

Question 14

What does s stand for in the t-test equation?

Answer 14

S = Standard deviation of sample

Question 15

What does x̄ stand for in the t-test equation?

Answer 15

x̄ = Mean of sample

Question 16

What does n stand for in the t-test equation?

Answer 16

n = number of measurements in sample

Question 17

If the spearman’s rank value is 0, what does this indicate?

Answer 17

No agreement whatsoever

Question 18

What range does spearman’s rank correlation coefficient give values between?

Answer 18

-1 and 1

Question 19

If the spearman’s rank value is close to 0, what does this indicate?

Answer 19

\+ = little agreement 
- = disagreement

Question 20

If the spearman’s rank value is 1, what does this indicate?

Answer 20

Perfect agreement

Question 21

If the spearman’s rank value is -1, what does this indicate?

Answer 21

Perfect disagreement

Question 22

What do standard deviation show?

Answer 22

The spread of data

Question 23

Why are standard deviations better than using a range?

Answer 23

Because SDs aren’t affected by outliers

Question 24

If the standard deviations overlap, what does this indicate?

Answer 24

Suggests the difference in means IS NOT significant

To be sure perform a t-test

Question 25

If the standard deviations do not overlap, what does this indicate?

Answer 25

Suggests that the difference in means IS significant

To be sure perform a t-test

Question 26

What are log scales used for?

Answer 26

When there is a big range of numbers

= makes them easier to plot on a graph