FOP - Statistical Analysis Lesson

 

Statistical Analysis

Why Use Statistics?

Statistics allow researchers to represent the data they have been collecting to back up their hypothesis. Sometimes they can also be used to distort the truth! Statistics provide a common language to organize, summarize, and make inferences about gathered data.

Descriptive Statistics

Descriptive statistics are used to summarize the data that psychologists collected from a study they conducted. They provide simple summaries of the samples and the measurements. Descriptive statistics can help psychologists recognize patterns that describe how often a behavior took place in the experiment.

Psychologists frequently use these descriptive statistics for the variables in their studies:

The central tendency is an estimate of the center of a group of measurements. It uses a single number to present the center. Measures of central tendency include mean, median, and mode. In a normal distribution (also known as a bell curve), the mean, median, and mode are all the same number, the highest peak of the curve of a bell-shaped polygon. Many characteristics of humans would graph to a normal curve, including the heights of adults or the IQs of all living people.  

The measures of variability include range and standard deviation. Range describes the distance from the highest to the lowest scores on a data set. If we are looking for the range of scores in a psychology class where the highest scoring student has an average of 96 and the lowest scoring student has an average of 51, the range for the class is 45.

Standard deviation describes how far each data point is from the mean. It measures how spread out a set of scores are. The lower the standard deviation is, the closer the data points are to the mean. A higher standard deviation indicates that the data points are spread out over a large range. In a normal distribution, approximately 68% of the scores are within 1 standard deviation (SD); 95% of the scores are within 2 SD; and 99.7% of the scores are within 3 SD from the mean.

Inferential Statistics

It is important that psychologists are able to apply the results of their experiment to the population. Inferential statistics give the psychologist an opportunity to apply their results. Are the results generalizable to the population they sampled? Researchers are looking for at least 95% assurance that their hypothesis can be supported. This can be illustrated with a P value of .05 or less and provides the borderline for statistical significanceStatistical significance is a statement of the likelihood that the independent variable actually did cause the change in the dependent variable. 

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