Descriptive statistics involves methods, that describe the central tendency and dispersion of data. In most practical cases they relate to single (univariate) variables.

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Data can vary in their nature. We differentiate between different levels. They could be either nominal, ordinal, interval or on ratio level. This really matters with regards to the statistical method you want you use.

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You always run your study based on a subset of the entire population, you intent to generalize on. External validity refers to the extent to which you really could do so. This in turn depends on the sampling methods you where using.

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Good research designs lead to a high internal validity. A study is internally valid when you really can assume the independent variable effects the dependent variable. Often you cannot.

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Research design relates to the architecture of your study. One major aspect is, whether you manipulate or just measure the independent variable.

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In systematic observation you observe people. Very often the subjects are not aware of the fact that they are being observed. Content analysis is about the consideration of existing material.

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Responding to questions is a complex process in psychological terms. Once you understand how people respond to questions you’ll see what to consider when creating questions.

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Creating a good survey is difficult. There is a clear roadmap on how you’d better do it. It involves various steps like defining the scope and related criteria. One essential step must be a pre-test.

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There are three criteria, which tell you something about the quality of your measurement. They are validity, reliability and objectivity. When estimating these criteria, you always use statistical correlation.

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In social science we often test variables. Think for instance of intelligence, personality and others. Testing is based on the classical test theory.

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