What is a correlationalresearch? It aims to look at an empirical relationship between two variables such that (1) changes in one are associated with changes in the other or (2) particular attributes of one variable are associated with particular attributes of the other. (Babbie, 2007) Not to be confused with „association‟ – Correlation has a specific technical meaning and needs statistical requirements for it, whereas association is a more general idea. (Neuman, 2011)
Why do we use a correlationalresearch? As a first step prior to experimentation As one of the criteria used to determine Nomothetic Casuality. When experiments cannot be conducted (for ethical or practical reasons)
A word of caution Correlational studies can suggest that there is a relationship between two variables, but they cannot prove that one variable causes a change in another variable. In other words, correlation does not equal causation.Out-of-class language English performance in learning class
How to conduct a correlationalresearch? Variables are identified Questions and/or hypotheses are stated A sample is selected Data are collected Correlations are calculated Results are reported
Step 1: Identifying Variables “Predictor” variable – the variable(s) that are believed to predict the outcome, also called independent variable “Criterion” variable – the variable to be predicted, the outcome, also called the dependent variable.
Step 2: Stating Questions Is level of education (independent variable) related to family income (dependent variable)? Do people who eat more eggs (independent variable) have higher cholesterol levels (dependent variable)? Do students who employ out-of-class strategies (independent variable) more often have higher English scores (dependent variable)?
Step 3: Sampling Random Sampling Convenient / Purposeful sampling A minimum of 30 samples is required
Step 4: Gathering data Naturalistic Observation Naturalistic observation involves observing and recording the variables of interest in the natural environment without interference or manipulation by the experimenter. The Survey Method In this method, a random sample of participants completes a survey, test, or questionnaire that relates to the variables of interest. Archival Research Archival research is performed by analyzing studies conducted by other researchers or by looking at historical patient records.
Step 5: Calculatingcorrelations To calculate a numerical value of a correlation we can use Pearson’s product moment correlation cooficcient or correlation coefficient with the symbol of the lowercase letter „r‟. A correlation coofficient ranges from - 1.0 to +1.0, with -1.0 indicating a perfect linear negative correlation and +1.0 a perfect linear positive correlation.
Interpretation of the Strength ofCorrelations 00 - .20 – Very Weak .21 - .40 – Weak .41 - .60 – Moderate .61 - .80 – Strong .81 – 1.00 - Very Strong Different statisticians may have similar but slightly different scales.
Step 6: Reporting results Positive Correlations: Both variables increase or decrease at the same time. A correlation coefficient close to +1.00 indicates a strong positive correlation. Negative Correlations: Indicates that as the amount of one variable increases, the other decreases (and vice versa). A correlation coefficient close to -1.00 indicates a strong negative correlation. No Correlation: Indicates no relationship between the two variables. A correlation coefficient of 0 indicates no correlation.
Correlations Scatter plots are often used to depict correlations 6000 5000 Calories per day This chart shows 4000 a strong positive 3000 correlation 2000 1000 0 100 150 200 250 300 350 400 Weight
Correlations Scatter plots are often used to depict correlations 160 This chart shows Minutes of Exercise per day 140 a strong negative 120 correlation 100 80 60 40 20 0 100 150 200 250 300 350 400 Weight
Correlations Scatter plots are often used to depict correlations 45 Miles from Krispy Creme 40 35 This chart shows 30 virtually no 25 correlation 20 15 10 5 0 100 150 200 250 300 350 400 Weight
How to calculate correlations Excel has a statistical function. It calculates Pearson Product Moment correlations. SPSS (a statistical software program for personal computers used by graduate students) calculates correlations.