Statistical Data Collection

Mr. CAF Reballos

Collection of Data

• Refers to the process of obtaining numerical measurements

Sources of Data

Sources of Data

• Documentary Sources– Information contained in published or

unpublished reports, statistics, internet, letters, magazines, newspapers, diaries and so on• Primary Data• Secondary data

Sources of Data

• Documentary Sources– Advantages of primary data over

secondary data• Primary data frequently give detailed

definitions of terms and accurate statistical units used in the survey• Primary data lend more relevance to the

researcher’s study• Primary data are more reliable

Sources of Data

• Field Sources– Include individuals who have sufficient

knowledge and experience regarding the study under investigation

Collecting Data: Methods

Methods of Collecting Data

1. Direct Method

– Face to face encounter between the interviewer and the interviewee

Methods of Collecting Data

1. Direct Method– Advantage:• Provides consistent and precise information• Questions may be repeated or modified

– Disadvantage:• Time consuming• Expensive• Has a limited field coverage

Methods of Collecting Data

2. Indirect Method– Method done by giving prepared

relevant questionnaires to the respondents of the study from which would like to get the needed information

Methods of Collecting Data

2. Indirect Method– Advantage:• Questionnaires may be mailed or hand-held• Inexpensive and can cover wide area in a

shorter period of time

– Disadvantage:• There is a strong probability of no response• Questions not easily understood will also

probably not be answered

Methods of Collecting Data

3. Registration Method– Method of utilizing the existing data or

fact or information which is kept systematized by the office concerned

– E.g. registration of births, death, motor vehicle, marriages, licenses

Methods of Collecting Data

4. Experiment Method– Used if the researcher would like to

determine the cause and effect relationship of certain phenomenon under investigation

– Used in making scientific inquiry

Planning the Study

1. Estimate the number of items in the population

2. Assess resources such as time and money factors, which are available to pursue the research

3. Determine the sample size needed in the study

Sample Size for Specified Margin of Error

N 1% 2% 3% 4% 5% 10%

500 222 83

1,500 638 441 316 94

2,500 1,250 769 500 345 96

3,000 1,364 811 517 353 97

4,000 1,538 870 541 364 98

5,000 1,667 909 556 370 98

6,000 1,765 938 566 375 99

7,000 1,842 959 574 378 99

8,000 1,905 976 580 381 99

9,000 1,957 989 584 383 99

10,000 5,000 2,000 1,000 588 385 99

50,000 8,333 2,381 1,087 617 397 100

Sample Size Determination

• A researcher in SJDEFI would want to make a survey in the school with a population of 1,000 students with a margin of error of 10 percent. How many students must he take into his sample?

Planning the Study

4. Pick the sample by using the appropriate sampling technique– Probability Sampling– Non-probability Sampling

Sampling Technique

1. Probability Sampling• Selecting a sample size (n) from a

population (N) such that each member of the population is given a non-zero chance of being included in the sample and all possible combinations of sixe (n) have an equal chance of being selected as the sample

Table of Random Numbers

Sampling Technique

2. Restricted Random Sampling• Used when the population is too

large to handle• Types:– Systematic sampling– Non-random sampling

Sampling Technique

2a. Systematic Sampling• The process of selecting the sample

when units are obtained by drawing every nth element of the population

• E.g. In a population of 50,000, the sample size is 100 at 10% margin of error. The nth item is 500.

Sampling Technique

2a. Systematic Sampling• Types:– Stratified sampling• population is divided into groups based on

homogeneity to avoid the possibility of drawing samples whose members come from one stratum

Sampling Technique

2a. Systematic Sampling• Types:– Stratified sampling• The distribution of sampling units is

proportional to the total number of units in each stratum

Sampling Technique

Stratified Sampling (Example)• Let us take a population of 50,000 families in

Tuguegarao City. Draw 100 sample units from this population with 10% margin of error. There are 25,000 families who belong to the high income group, 10,000 families in the middle income group and 15,000 in the low income group

Sampling Technique

2a. Systematic Sampling• Types:– Cluster sampling• Districts or blocks constitute the cluster• Is useful in selecting the sample when

heterogeneous groups occupy blocks in a community or city

Sampling Technique

2a. Systematic Sampling• Types:–Multi-stage sampling• Uses several stages or phases in getting the

samples from the general population• Is useful in conducting a nationwide survey

or any survey involving a large universe

Sampling Technique

2b. Nonprobability Sampling• Technique wherein not all members

of the population are given equal chances to be selected at sample

• Researcher states his prejudice in the choice of the sample

Sampling Technique

2b. Non-probability Sampling• Types:– Quota sampling

• Researcher limits the number of his samples based on the required number of the subject under investigation

– Purposive sampling• Sampling is based on certain criteria and rules

laid down by the researcher

Sampling Technique

2b. Non-probability Sampling• Types:– Convenience sampling• The researcher conducts a study at his

convenient time, preferred place or venue

Planning the Study

5. Prepare the questions to be asked in the interview or in the questionnaire

Types of Questions

Structured Question• Type of question that

leaves only one way or few alternative ways of answering

• The questions are clear, simple and objective

Types of QuestionsUnstructured or

Open Ended Questions

• Questions that can be answered in many ways – probing questions or questions that want to elicit reasons