Chapter 3

CENSUS AND SAMPLE METHODS OF DATA COLLECTION- CLASS XI

1. CHAPTER-3 CENSUS AND SAMPLE METHODS OF DATA COLLECTION

2. What are we going to study in this chapter? Different techniques of data collection Census method Sample method Types of sampling methods Sampling and non sampling errors

3. CENSUS METHOD DEFINITION A survey which includes every element of the population is known as census or method of complete enumeration. Under this method , data is collected for each And every unit of the investigation

4. EXAMPLES The census of india is conducted Every 10 years. It is available on Various subjects : population, Economy, finance,literacy , sex ratio etc. Every five years , an agricultural Census is conducted in india . First such census was conducted in 1970s

5. MERITS OF CENSUS METHOD Complete information can be obtained about the whole population. Data obtained from this method are more reliable, accurate and representative. In census method, no item is left out so, the data is more adequate. This method is quite useful when the field of study is not big and intensive Survey is to be made. 5. Data obtained from the complete enumeration can be used in other Investigations.

6. DEMERITS OF CENSUS METHOD It is more expensive and time consuming method of data collection. It is not applicable if population size is infinite . It contains errors due to non response , biaseness of respondents. Some errors or wrong information may enter in an inquiry due to less Efficiency of enumerator .

7. SAMPLE METHOD DEFINITION Sample method refers to the process Of learning about the population on The basis of sample drawn from it. In sampling method, instead of every Item of the universe only a part of the Universe is studied and the conclusions Are drawn on the basis of it.

8. example

9. MERITS OF SAMPLE METHOD It is more economical because we do not have to collect all data. As no. Of units is only fraction of total universe , Time consumed Is also fraction of total time. 3. If sample is taken properly, the results are very reliable and accurate. 4. This method is specially used for infinite, hypothetical and perishable Universes.

10. DEMERITS OF SAMPLE METHOD If the sample is not representative, the results will not be correct. These will Lead to the wrong conclusions . Sometimes the universe is so small that the proper samples cannot be taken. It is a scientific method. Therefore, to get a good and representative sample, one should have special knowledge to get good sample and to perform proper analysis so that reliable result may be achieved. As in many cases the investigator, chooses samples, such as convenience method, chances of personal bias creep in. It creates a new type of error i.E , ‘ sampling error ’ or ‘ random error’.

11. Probability samples Definition A probability sampling scheme is one in which every unit in the population has a chance(p>0) Of being selected in the sample, and this probability is known. In this method, subset is selected on the basis of some logic. Example : if a researcher wants to select 10 students out of 70 students in a class, he can choose them using any logic such as students having age above 20; students from first row , students scoring more than 80% etc.

12. Simple random sampling Definition It is that method of sampling in which each and every item of the universe has an equal chance of being Selected. In other words, there is an equal probability for every item of the universe . Example : LOTTERY METHOD Each member of the population is assigned a unique number or a code. Then slips are prepared bearing those numbers. They are placed in a box and shuffled properly The investigator then picks up a slip randomly That’s how a desired sample can be selected randomly

13. RANDOM NUMBER TABLES Another method of random sampling is Using the random number tables given by Tippit , yates or fisher. Tippit’s random no. Table consists of 10,400 four digited numbers, giving in All 10,400*4= 41600 digits selected at Random. Suppose we have to select 2 out of 10 students in a class. Assign no. To each student. Now largest no. Is 10 which is two digit. We can randomly select a spot to start From. IV. Suppose we start from 3 rd no. In 1 st column i.E ; 2370. Now we will consider only first two digits. We can move row wise or Column wise. As 23> 10 we’ll not consider it. V. Moving column wise and leaving the no. Greater than 10 , we can select 2 Numbers i.e ; 5 & 10 .

14. Systematic sampling Definition According to this method, units of the population are numerically, geographically, and alphabetically arranged. Every nth item of the numbered items is selected as a sample item. Example : 10 out of 100 students selected at random for this one can take 5 th , 15 th ,….., 95 th . Select any starting point and then select every nth element of the population .

15. Stratified sampling Definition According to this method of sampling, population is divided into different strata having different characterstics and some of the items are selected from each strata, so that the Entire Population gets represented. male female

16. Cluster/area sampling Definition In this technique, the total population is divided into groups or clusters and a simple random sample of the cluster is selected. When sub divisions are meant to be some geographical area, then cluster sampling is known as area sampling.

17. NON PROBABILITY SAMPLING DEFINITION Non probability sampling is a technique where the chances of any member being selected for a sample cannot be calculated. It is based on the subjective judgement of the investigator. Example: accidental or haphazard sampling

18. JUDGEMENTAL/PURPOSIVE SAMPLING DEFINITION It is a sampling technique in which researcher relies on his or her judgement When choosing members of population to participate in the study . In this method, selection of the sample items is not left out to the chance factors but simply made by choice. It is also known as deliberate ,selective or subjective sampling. Example: for examining extreme poverty levels of draught prone Area of haryana ,some districts are purposively chosen and compared with the other Normal districts of the state.

19. CONVENIENCE SAMPLING DEFINITION It is a non probability sampling technique in which items are selected on the basis oftheir convenient accessibility and proximity to the researcher. It is also known as availability sampling. Examples : online poll, survey your best friends, asking for volunteers at the mall.

20. QUOTA SAMPLING Definition In this method, the population is divided into different groups according to different characteristics of the population. Then, the investigators are simply given the quotas to be filled from each group. The size of the quotas is generally proportionate to the size of the group in the population. Example: a class XI has 100 students Non medical - 20 Medical - 10 commerce - 30 arts - 40 Now there are 4 subgroups , an investigator selects a sample proportionately Non medical - 4 Medical - 1 Commerce - 9 Arts - 16

21. SAMPLING ERRORS BREAKING DOWN 'Sampling Error' Sampling error can be eliminated when the sample size is increased and also by ensuring that the sample adequately represents the entire population. A sampling error is a statistical error that occurs when an investigator does not select a sample that represents the entire population of data and the results found in the sample do not represent the results that would be obtained from the entire population . SAMPLING ERROR Estimated value of parameter – true value of parameter

22. NON SAMPLING ERRORS DEFINITION Non-sampling errors can be defined as errors arising during the course of all survey activities other than sampling. These are the errors related to the collection of data. These are of following types: Error of measurement Error of non response Error of misinterpretation Error of calculation or arithmetical errror

23. Why stratified sampling is known as mixed sampling? This method involves the mixture of both purposive sampling and random Sampling.The division of population into different strata is purposely done while selection of the items is done at random.

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