Stats

Question 1

Why is SD more useful than range?

Answer 1

SD takes into account all data point
less effected by outliers
SD can be used to determine if results are significant or not- allows statical test to be carried out

Question 2

How do scientists determine how many trials are appropriate?

Answer 2

• test different numbers of trials
• select which ever gives best results in appropriate time / number of trials after which there is no change in sample collected

Question 3

Gives reasons for carrying out repeats

Answer 3

• exclude anomalous results
• calculate more reliable mean
• allow statistics to be carried out
• check results are concordant

Question 4

Evaluate mean as a measure of average

Answer 4

• takes into account all data so gives accurate representation
• distorted by outliers
• useful for comparison’s
• gives no indication of the range

Question 5

Evaluate median as a measure of average

Answer 5

• less effected by outliers

- not suitable for small data sets with large variation

Question 6

Evaluate mode as a measure of average

Answer 6

• unaffected by outliers
• may not give accurate representation of data set
• could be multiple or no mode

Question 7

Give a reason why student t test is the appropriate statistical test for this investigation

Answer 7

testing significant difference between TWO MEANS

Question 8

Give a reason why Spearman’s rank is the appropriate statistical test for this investigation

Answer 8

testing significant correlation between two DIFFERENT CONTINUOUS variables

Question 9

Give a reason why chi-squared is the appropriate statistical test for this investigation

Answer 9

testing significant difference between CATEGORICAL data

Difference between observed and expected frequencies, establish if difference is significant

Question 10

Describe how a statistical test would be used to find a significant correlation or difference (in means or frequencies)

Answer 10

construct a null hypothesis

• carry out statistical test to calculate test statistic ( t-test, spearman’s, chi-squared)
• look up value in critical value table for p=0.05
• use figure to accept or reject null hypothesis (if test statistic is greater than critical value then reject null hypothesis)

Question 11

Why is a large sample size good?

Answer 11

Smaller the probability that chance will influence results

Less influence outliers will have, anomalies easier to be undefined