The Roberton sample was obtained by stratified random sampling with the strata based proportionally on age groups. This type of sampling may be necessary for investigating the average reaction time. What had to be known in order to achieve this? (Select 1 or more correct answers) Question 5 Select one or more: a. Age is not relevant to the condition investigated and therefore will have no effect on reaction time or cognition b. A sampling frame which divides the population into a set of different coherent areas and randomly selects areas to assess. c. Age is often referred to as "the universal confounder" - so reaction time might be effected by age. d. Stratified sampling allows for the sampling to be random within each sub-group being investigated (in this case, each age group) - so the proportions of the different age groups are the same in the population and the sample. e. A sampling frame of the entire population, along with their age and the proportions of each age sub-group in the population is needed to achieve this stratified sampling. f. Stratified sampling allows for sequential order within the sample which ensures that the attribute studied is random