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C81MPR Practical Methods (Lab 2) Collecting Data. Dr. Danielle Ropar & Dr. Jonathan Stirk. Introduction. The aim of this part of the practical is to explain data collection There are two sources of data that you should consider Individual subject data Group data. Individual subject data.
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C81MPR Practical Methods (Lab 2)Collecting Data Dr. Danielle Ropar & Dr. Jonathan Stirk
Introduction • The aim of this part of the practical is to explain data collection • There are two sources of data that you should consider • Individual subject data • Group data
Individual subject data • When we collect data from a single participant to measure a particular behaviour we can collect: • One single data point per participant • Several data points per participant
One data point • Sometimes it is possible to collect only one data point per subject • For example • Height • IQ • Race
Problems with one data point • Collecting only one data point is sensible when you are certain that your measurement is accurate • If there is any reason to believe that your measurement is not always accurate then it is necessary to take several measures
Several data points per participant • Collecting more than one data point per participant is useful because: • The estimate of the performance of the participant is less prone to the impact of random variation
Group data • Usually there is more than one subject in an experiment • Collecting data from several subjects has the same advantages as collecting several data points from each subject: • The estimate of the performance of the participants is less prone to the impact of random variation
How many participants should there be? • The number of subjects required in an experiment is dependent upon • The statistical test to be used • The level of significance required • The probability of the alternative hypothesis being true • The size of the effect being examined • This information is either gleaned from a search of the literature or based upon the requirements of the researcher
Number of participants in practicals • For the purposes of first year practicals there should be 16 participants per group • This number is usually (but not always) big enough to use the appropriate statistical procedures • This is only a rule of thumb. For real research the proper calculations should be conducted (Using a procedure called a pre-hoc power analysis)
Summary • Data is collected from single participants • Whenever possible more than one data point should be collected at each level/condition of the experiment • Data is collated from groups of participants • There should always be sufficient participants for the particular experiment in mind