Methods of collecting Statistical Data

1. Complete Enumeration:
If the required information is obtained from each and every unit in the population then this is known as complete enumeration.

2. Sample Survey:
If the required information is obtained from only a part of the population (sample units) then this is known as sample survey.

DATA Types

1. Primary Data:
The data which is originally collected and have not gone through any statistical process is known as primary or raw data.

Procedures to collect primary data

1.1 Direct Personal Investigation:
In this method, the required information is obtained directly from the individual or object concerned.

1.2 Indirect Investigation:
If the required information involves sensitive information, people may not give the correct information or refuse to respond at all. In such case the required information is obtained from people close to the person concerned.

1.3 Questionnaire Method:
In this method, a questionnaire which consist questions relevant to required information is give to the people with the request to return the filled questionnaire within a give period.
This method is used for area where educated people live.

1.4 Collection through Enumerators:
In large scale surveys, trained enumerators are used to obtain the required information.

2. Secondary Data:
The data which have been already collected and have undergone through any statistical treatment is known as secondary data.

Sources of secondary data:

2.1 Official Sources:
Examples are Ministry of Agriculture, federal bureau of statistics etc…

2.2 Semi-Official Sources:
State Bank of Pakistan, WAPDA, HEC etc…

2.3 Private Organizations:
NGO’s, Chamber of Commerce, Banks etc…

Classification

“The process of dividing the observations into groups or classes is known as classification.”

Why we need to classify?

Let suppose we have result of 10,000 students with us. We can’t remember the marks obtained by all students. Now what If someone asks how was the result? How many students did pass? How many were failed? What were the average marks?
To answer these questions we have to summarize our data or we can say classify it. Then we can easily answer the asked questions.

Frequency Distribution:

“A table listing all the values or groups of values of variable along with number of observations of each value or group of value is known as frequency distribution.”

Steps to construct Frequency Distribution:

1. Find the range of the data
2. Decide the number of classes; approx number of classes = 1+3.3 log10 n
3. Obtain class interval size by dividing the range by number of classes.
4. Form the classes such that the smallest and the largest observations are covered.
5. Distribute original data into classes by tally marks.