Tutorial Letter 201/1/2018 Psychological Research PYC3704 Semester 1 Department of Psychology

A 'formula' is more properly referred to as an equation. This term implies that what is on the left hand side of the formula must be set equal to what is written on the right hand side. It represents a concise description of a calculation which you need to perform, displaying the variables you need to consider and the relationships among them. Think of it as a system which tells you how to calculate something in a very precise way. You have to learn how to use it, and this is something you learn by doing, not just by looking at it.PYC3704/201 3 Each symbol in such an equation represents a variable, and you need to find the current value of that variable based on the data which you have. First you substitute the symbol with that number. Then you have to perform the calculation, which is an arithmetic procedure, making use of operations like adding, subtracting, division, multiplication, calculating square roots and so on (see Appendix E in the PYC3704 Guide). Let us first consider a simple example. Look for at the formula for the mean of a sample of data (given in Appendix C in the Guide): The symbol ¯x is a conventional way to indicate a mean (some books use the symbol M for this). Each of the symbols on the right hand side of the equation is to be replaced by a number. Σx is a conventional way of writing 'the sum of all the x-values' (see Appendix E in the Guide). To do the calculation you would need to have a set of data representing various measurements of the variable indicated by 'x'. So what this formula tells you is that the mean of the x-values is calculated by adding them up and dividing the result with n (which is equivalent to multiplying the result with 1/n).