P5 Planning, Analysis & Evaluation

Question 1

Similarities & differences between standard error (SE) and standard deviation

+ 2 additional advantages of sd

Answer 1

❖ standard error shows the closeness of sample to population (true) mean
❖ standard deviation shows the spread of data about the mean
3. both SE & sd indicate the reliability of data {mean for SE}
4. both are used to plot ERROR BARS on graph

Standard deviation
+ Allows calculation of standard error / confidence intervals
+ Allows t-test to be calculated

Question 2

4 pieces of information gained by calculating confidence intervals (CI)
95% CI = mean +- 2 SE

Answer 2

1. 95% confident that the mean lies within these limits
2. show the reliability of the MEAN
3. __mean is more reliable b/c error bar is smaller
4. difference between means (aka t-test) is significant b/c there is no overlap between CI for __ and __

Question 3

3 reasons why a numeric scale is used to record, eg. the degree of damage to trees

Answer 3

1. to allow easier comparison of data
2. to allow easier analysis of results
3. easier to plot as graph/bar chart

Question 4

7 constant variables to ensure results from gel electrophoresis can be compared

Answer 4

1. volume of DNA sample added to wells
2. time allowed for samples to run on gel
3. type of buffer solution
4. volume of buffer
5. voltage difference used for electrophoresis
6. thickness of gel
7. temperature

Question 5

Starting with a stock solution, outline how you would make a serial dilution to produce a range of concentrations. [2m]

Answer 5

• put a standard volume of stock solution into a standard volume of water
• use new dilution for making the next dilution in the same way as above

Question 6

Suggest why it is important that the test subjects should not know whether they are having a drink with caffeine or without caffeine. [1m]

Answer 6

Results could be affected by subject expectation

Question 7

How to determine sensitivity of bacteria to each antibiotic?

Answer 7

1. Measure diameter of clear zone around antibiotic disc with a ruler
2. The wider the clear zone, the more sensitive the bacteria to antibiotic
3. No clear zone means bacteria are resistant to antibiotic

Question 8

2 reasons why it is possible to use Spearman’s rank correlation

Answer 8

1. Data can be ranked

2. At least 5 pairs of data

Question 9

Reasons/evidence to…
support conclusion?

suggest conclusion is not valid?

Answer 9

Support

1. Large sample size
2. Data collected over long period of time
3. __ factors are the same

Do not support

1. Small sample size / insufficient replicates
2. Not all age ranges included
3. Only females/males (gender bias)
4. Short duration of investigation
5. Std dev.s of 2 groups overlap
6. Method of collecting data is inconsistent, eg. diff. apparatus

Inconclusive: No statistical test carried out

Question 10

4 reasons why Pearson’s linear correlation test is suitable for the data

Answer 10

1. Data are continuous
2. Data are normally distributed
3. Scatter graph shows a linear correlation
4. 5 or more paired observations