高等教育：教育心理统计研究课件Lecture5

1、Lecture 5Summarizing dataFrequency distributionsThe idea of a frequency distribution is to tell us the number of cases in each category By frequency is simply meant the number of times that something occurs. Very often we also need to compute percentages, which tell us the proportion of cases contai

2、ned within each frequency.Using SPSS to produce frequency tables andhistogramsIn order to generate a frequency table for income, we will need to group the data; otherwise we will get a frequency count and percentage for every single income in the sample We would have separate bars for each income wi

3、thin the sample. To group the data, we will need to use the Recode procedure In doing this, we will be creating a new variable which will be called incomegp The aim is to group people into different income groups: &5,000 and below; $6,000-6,999; $7,000-7,999; $8,000-8,999; $9,000 and above The follo

4、wing sequence will accomplish this:T ransform RecodeInto different variables=-Variable nameChangeOld and new values=- Range.OKUsing SPSS to produce frequency tables andhistogramsThe following sequence will generate the frequency table output:Analyze = Descriptive statistics =-Frequenciesa OKUsing SP

5、SS to produce frequency tablesand histogramsFor a histogram of income, the following sequence should be followed:Frequencies-Charts=-Histograms= OKAn alternative way of presenting data relating to a nominal variable is a pie chart, which displays the number of cases in each category in terms of slic

6、es of a circleFrequencies =-Charts =Pie charts =- OKMeasuring central tendencyOne of the most important ways of summarizing a distribution of values for a variable is to establish its central tendency the typical value in a distributionThree measures of average are usually discussed: the arithmetic

7、mean, the median and the mode.MeanThe arithmetic mean is a method for measuring the average of a distribution which conforms to most peopled notion of what an average is.MedianThe median is the mid-point in a distribution of values. It splits a distribution of values in half. When there is an even n

8、umber of values，the average of the two middle values is taken.ModeThis final indicator of central tendency is rarely used in research reports, but is often mentioned in textbooks. The mode is simply the value that occurs most frequently in a distribution.Measuring dispersionDispersion can provide us

9、 with important information. For example, we may find two roughly comparable firms in which the mean income of manual workers is identical. However, in one firm the salaries of these workers are more widely spread, with both considerably lower and higher salaries than in the other firm. Thus，althoug

10、h the mean income is the same，one firm exhibits much greater dispersion in incomes than the other.The most obvious measure of dispersion is to take the highest and lowest value in a distribution and to subtract the latter from the former. This is known as the range.Analyze Descriptive statistics exp

11、lore -Dependent list=OKThe following items that have been covered above will be produced: mean, median, range, minimum and maximum, standard deviation, and the inter-quartile range (IQR).The shape of a distributionIt is important to realize that some variables will not follow the shape of the normal

12、 distribution curve. This tendency is most clearly evident when the values in a distribution are skewedthat is, they tend to cluster at either end. When this occurs, the mean and median no longer coincide.The shape of a distributionPositively and negatively skewed distributionsThe shape of a distrib

13、utionAnalyze =-descriptive statistics，=Frequencies SkewnessIf there is no skew, or in other words if the variable is normally distributed, a value of zero or nearly zero will be registered. If there is a negative value, the data are negatively skewed; if the value is positive, the data are positivel

14、y skewed On the other hand, this test is not easy to interpret and there is much to be said for a visual interpretation of the data to discern excessive skew This can be done through a frequency table, or through a diagrammatic presentation, such as a histogram.Exercises1 What is the appropriate SPSS procedure f