A level biology statistical tests.pptx

t test, r test for A -level biology are covered

1. Statistical tests The statistical tests are used to assess the level of confidence on data sets. The three key tests : Chi-square test (x 2 ) Student t-test (t) Correlation coefficient calculations ( r )

2. Chi-squared (x 2 ) test Student t test Correlation coefficient (r ) test Compares the observed pattern with the chance pattern in data . Judges the significance of any difference between the means of data sets of two different groups. Determines the existence of correlation between any two data sets. df = n – 1 n = number of categories df = (n 1 + n 2 ) – 2 n 1 = mean of the first data set n 2 = mean of the second data set df = n – 2 n = number of the data point in both variables Enough data for a reliable mean The data normally distributed The sample size need not to be equal Statistical test: For each of the three tests the relevant quantities are calculated using Mathematical formulas given in the table. The calculated values compared against the standard probabilities tables allow interpretation of the data in a statistically informed way.

3. Q: 1. Scientists used a statistical test to determine whether there was a significant difference in the amino acid concentration in two types of white wine. They obtained a p value of 0.04. Name the statistical test the scientists used and give a reason for your answer. Was the difference significant? Give a reason for your answer. Name of the statistical test : Student t-test Reason for choice : Since the investigation requires comparison of means of two data sets. Explanation of test result : Since the p value is below 5% (0.04), the Null hypothesis is rejected and therefore, the difference is significant. Past paper example: 1

4. Q:2. Doctors carried out a statistical test to determine whether the antibody concentrations were significantly different in girls given two doses of vaccine, compared with those given three doses. They determined the mean concentrations of antibody 9 months after the first dose of vaccine. What statistical test the should the doctors have used? Student-t test as the investigation involves comparison of means of two data sets. Give the reason for your choice: as the investigation involves comparison of means of two data sets. Past paper example: 2