Р. П. Мильруд Доктор педагогических наук, профессор кафедры иностранных языков

The sampling techniques can be divided into two types: 
− probability or representative sampling; 
− non-probability or judgemental sampling. 
Choice of sampling technique or techniques is dependent on your research question(s) and objectives: 
− probability samples are required if you need to estimate statistically the characteristics of the population from a 
sample; 
− if you do not require such generalisations you can make use of non-probability sampling techniques. 
Factors such as the confidence that is needed in the findings, accuracy required and likely categories for analyses 
will affect the size of the sample that needs to be collected: 
− statistical analyses usually require a minimum sample size of 30; 
− research question(s) and objectives that do not require statistical estimation may need far smaller samples. 
Sample size and the technique used are also influenced by the availability of resources, in particular financial sup-
port and time available to select the sample and to collect, enter into a computer and analyse the data. 
Probability sampling techniques all necessitate some form of sampling frame, so they are often more time consum-
ing than non-probability techniques. Sampling frame is the complete list of all the cases in the population, from which a 
probability sample is drawn. Where it is not possible to construct a sampling frame you will need to use non-probability 
sampling. 
2. If your research question(s) and objectives are concerned with what people do, an obvious way in which to dis-
cover this is to watch them do it. This is essentially what observation involves: the systematic observation, recording, 
description, analysis and interpretation of people’s behaviour. 
There are two types of observation. 

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