Fundamentals of Statistics contains material of various lectures and courses of H. Lohninger on statistics, data analysis and chemometrics......click here for more. 
Home Basic Concepts Definition of basic terms Frequency  
See also: Frequency Polygons, Histogram, Contingency Table, Random Variable  
FrequencyFrequencies of occurence form the basis of many statistical procedures and approaches for interpreting data, because they reflect physical, social, political, biological (or whatever) realities. When describing frequencies we have to distinguish two cases:
On the other hand, for continuous variables the number of different measurement values may be of the same order as the number of observations. For example, the body weight of the 120 students will result most probably in 120 different values if we determine the weight with a precision of one gram, since the chance to find two persons having exactly the same weight (down to the gram level) will be very low. In this case we will have to assign categories (classes) to the weights simply by specifying ranges along the weight scale. The counts of observations falling into these classes are then the frequencies.^{(1)} Now, what do we mean by frequency? The absolute frequency n_{i} is the number of observations belonging to a category a_{i} or falling into a particular class c_{i}. The sum of all frequencies of all categories/classes is equal to N, the total number of observations: Σn_{i} = N Relative freqencies f_{i} are obtained by normalizing the individual frequencies to a total sum of 1.0 (or 100%, respectively). This way the frequencies become independent of the sample size and will be comparable to each other.Frequencies are usually delineated in a frequency table or displayed as a histogram. The frequency table contains the absolute and the relative frequencies n_{i} and f_{i} for all categories a_{i}: a_{1} n_{1} f_{1} a_{2} n_{2} f_{2} a_{3} n_{3} f_{3} .. .. ..


Home Basic Concepts Definition of basic terms Frequency 