Tip 1: How to build a correlation field

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Tip 1: How to build a correlation field

If you assume that between characteristicsprocess or indicators there is a relationship, you can build a schedule that will reflect it. A graph that establishes a relationship between variables is called field correlations.

You will need

- a series of distributions from a dependent and independent variable;
- paper, pencil;
- A computer and a program for working with spreadsheets.

Instructions

Select two variables, between which, like youbelieve there is a relationship, usually take values that vary with time. Note that one of the variables must be independent, it will act as a reason. The second in this case must change synchronously with it - decrease, increase or change randomly.

Measure the value of the dependent variable foreach testimony is independent. Record the results in a table, in two rows or two columns. To detect the presence of a link, you need at least 30 indications, but to get a more accurate result, take care of the presence of at least 100 points.

Construct a coordinate plane, while on the ordinate axis postpone the values of the dependent variable, and on the abscissa axis - independent. Sign the axes and specify the units of measure for each indicator.

Mark the points of the correlation field on the graph. On the abscissa, find the first value of the independent variable, and on the ordinate axis - the corresponding value of the dependent variable. Construct perpendiculars to these projections and find the first point. Mark it, circle it with a soft pencil or pen. Similarly, construct all the other points.

The resulting set of points is called the correlation field. Analyze the resulting schedule, draw conclusions about the presence of a strong or weak causal relationship, or its absence.

Pay attention to random deviations fromgraphic arts. If, on the whole, a linear or other dependence is traced, but the whole "picture" is spoiled by one or two points that are not on the whole, they can be recognized as random errors and not taken into account when interpreting the graph.

If you need to build and analyze a field correlations for a large amount of data, use programs designed for working with spreadsheets, for example, Excel, or purchase special programs.

Tip 2: What is correlation

The interrelationship of several quantities, during whichThe change in one leads to a change in the rest, is called a correlation. It can be simple, plural or partial. This concept is accepted not only in mathematics, but also in biology.

Word correlation from the Latin word correlatio, thatmeans interconnection. All phenomena, events and objects, as well as the quantities that characterize them, are interrelated. The correlation dependence differs from the functional one in that in this type of dependence, the consequences of any events can be measured only on average, approximately. The correlation dependence assumes that the variable corresponds to changes in the independent quantity with only a certain degree of probability. The degree of dependence is called the correlation coefficient. In biology, the concept of correlation is the relationship between the structure and functions of individual parts of the organism. Quite often the concept correlation enjoy statistics. In the statistics, this relationship between statistical variables, series and groups. To determine the presence or absence or presence of a correlation, a special method is used. The correlation method is used to determine the direct or reverse parallelism in the changes in numbers in the series that are compared. When the correlation coefficient is found, measure the measure itself or the degree of parallelism. But the internal cause-effect factors in this way are not sought. The main task of statistics as a science is to help to discover such causal dependencies to other sciences. In form, the correlation can be linear or nonlinear, positive and negative. When one of the variables increases or decreases the other, it increases or decreases, then the relationship is linear. If, with a change in one value, the nature of the changes in the other is non-linear, then this correlation nonlinear. Positive correlation is considered when raising the level of onemagnitude is accompanied by an increase in the level of the other. For example, when the sound amplification is accompanied by a sensation of increasing its tone. Correlation, when the increase in the level of one variable is accompanied by a decrease in the level of the other, is called negative. In animal communities, an increased level of anxiety of the individual leads to the fact that the probability of occupying this individual of the dominant niche among the brethren is reduced. When the relationship of the variables is absent, correlation carries the names zero.

Tip 3: How to calculate the correlation

Correlation is the mutual dependence of tworandom variables (more often - two groups of quantities), in which changing one of them leads to a change in the other. The correlation coefficient shows how likely the change in the second quantity is when the values of the first are changed, i.e. the degree of its dependence. The easiest way to calculate this value is to use the corresponding function built into the Microsoft Office Excel spreadsheet.

You will need

Microsoft Office Excel spreadsheet.

Instructions

Start Excel and open the document that containsgroup of data, the correlation coefficient between which you want to calculate. If no such document has been created yet, then enter the data in an empty table - the table editor creates it automatically when the program starts. Each of the groups of values, the correlation between which you are interested, enter into a separate column. It does not have to be adjacent columns, you are free to make the table in the most convenient way - add additional columns with explanations to the data, column headers, summary cells with summary or average values, etc. You can even have the data not in the vertical (in columns), but in the horizontal (in rows) direction. The only requirement that must be met is that the cells with the data of each group must be arranged one after another in order to create a continuous array in this way.

Go to the cell that will becontain the correlation value of the data of two arrays, and click the "Formulas" tab in the Excel menu. In the "Function library" group of commands, click the most recent icon - "Other functions". A drop-down list will appear in which you should go to the "Statistical" section and select the CORREL function. As a result, the Wizard window opens with a form to fill. The same window can also be called without the "Formula" tab, simply by clicking on the function insert icon located to the left of the formula line.

Specify the first group of correlated data in the field"Array1" of the Formula Wizard. To enter a range of cells manually, type the address of the first and last cells, separating them with a colon (without spaces). Another option is to simply select the desired range with the mouse, and place the necessary entry in this field of the Excel form yourself. The same operation should be performed with the second group of data in the field "Array2".

Click OK. The table editor calculates and displays the correlation value in the cell with the formula. If necessary, you can save this document for later use (keyboard shortcut Ctrl + S).