Applying statistical techniques

Applying statistical techniques

1. Why use statitsical test? It can help to determine whether the difference observed is a significant difference or simply natural variation

2. Standard deviation

   • Measures the amount of variation or spread from the mean
   • Low standard deviation= narrow range and aare closely grouped to the mean, could indicate greater reliabilty
   • Calculating S.D
     • • s= standard deviation, x= individual value, x= mean value and n=number of data points
     • Spread of data is the mean + or - S.D
     • If it shows a normal distribution: 68% should lie within 1 S.D and 95% should lie within 2 S.Ds

3. Students t-test

   • • Where x is the mean of data set 1, s is the S.D of data set 1 squared, n is the number of data points in the first set of data
   • Used to compare 2 means, it will tell us if the difference between the two means is a significant differences. State a null hypothesis and then the t-test will say whether we accept or reject the null hypothesis
   • Is this significant? degrees of freedom= sample size - number of data sets. Then we use the table of t-values to assess whether the calculated value indicates a significant difference. If its greater than the value at 5% then its significant then we can reject the null hypothesis

4. Correlation coefficient

   • Used to consider the relationships between the 2 sets of data, spearman rank correlation tells us whether 2 sets of data are correlated or not
   • • r =rank coefficient, D= difference between the ranks, n= number of pairs of values
   • Then use the table of critical values, if it is below the critical value then there is no significant correlation