Unit 2: Data Collection Flashcards
Classification of statistical data
- Primary vs. Secondary
- External vs. Internal
data measured by the researcher / agency that published it.
primary data
any republication of data by another agency.
secondary data
information that relates to the operations and functions of the organization collecting the data.
internal data
information that relates to some activity outside the organization collecting the data.
external data
General classification of collecting data
Census and sample survey
a.k.a. complete enumeration
- is the method of gathering the information of interest or pertinent data from every unit in the population.
census
method of gathering data from a small but representative cross section of the population.
sample survey
advantages of sample survey
Speed and timeliness
- data on the population can be gathered faster ensuring uniformity.
Economy
- information gathering and data analysis is cheaper.
Quality and accuracy
- when properly conducted, a sample survey usually yields more accurate results since a small highly skilled group of workers is likely to make fewer errors in the collection and handling of data than a large census force would.
Feasibility
- some data gathering methods require the destruction of a unit to obtain the required information, e.g., lifetime of a bulb.
Methods of collecting statistical data
Survey method
Observation method
Experimental method
Use of existing studies
Registration method
questions are asked to obtain information.
survey method
ways to administer survey
telephone interview
mailed questionnaire
online survey
personal in-home survey
personal mall intercept survey
makes possible the recording of behavior but only at the time of occurrence
observation method
- a method designed for collecting data under controlled conditions.
- is an operation where there is actual human interference
with the conditions that can affect the variable under study.
experiments
e.g., census, health statistics, and weather bureau reports.
Documentary sources - published or written reports, periodicals, unpublished documents, etc.
Field sources – researchers who have done studies on the area of interest are asked personally or directly for information needed
use of existing studies
e.g., car registration, student registration, and hospital
admission.
registration method
Sampling methods
- non-probability
- probability
- not all members of the population have a chance to participate in the study
- often used in exploratory and qualitative research.
non-probability sampling
- every element of the population a (known) nonzero chance of being selected in the sample
- often used in quantitative research
probability sampling
population from which information is desired.
target population
collection of elements from which the sample is taken.
sampled population
listing of all the individual units in the population.
population frame
sets out to make a sample agree with the profile of the population based on some pre-selected characteristics
purposive sampling
selects a specified number of sampling units possessing certain characteristics.
quota sampling
selects sampling units that come to hand or are convenient to get information from.
convenience sampling
selects sample in accordance with an expert’s judgment.
judgment sampling
a sampling method which existing subjects provide referrals to recruit samples required for a research study.
snowball sampling
commonly used probability sampling methods are:
- Simple random sampling
- Stratified random sampling
- Systematic sampling
- Cluster sampling
- Multistage sampling
method of selecting n units out of the N units in the population in such a way that every distinct sample of size n has an equal chance of being drawn. The process of selecting the sample must give an equal chance of selection to any one of the remaining elements in the population at any one of the n draws.
Simple Random Sampling
Explain the process of simple random sampling
Step 1: Make a list of the sampling units and number them from 1 to N.
Step 2: Select n numbers from 1 to N using some random process, for example, the table of random numbers. n is distinct for SRSWOR, not necessarily distinct for SRSWR.
Step 3: The sample consists of the units corresponding to the selected random numbers.
method of selecting a sample by taking every kth unit from an ordered population, the first unit being selected at random.
Here k is called the sampling interval; the reciprocal 1/k is the sampling fraction.
1-in-k Systematic sampling
Explain the linear process of systematic sampling
Method A
Step 1: Number the units of the population consecutively from 1 to N.
Step 2: Determine k, the sampling interval using the formula k = N/n.
Step 3: Select the random start r, where 1 ≤ r ≤ k. The unit corresponding to r is the first unit of the sample.
Step 4: The other units of the sample correspond to r + k, r + 2k, r + 3k, and so on.
Explain the circular process of systematic sampling
Method B
Step 1: Number the units of the population consecutively from 1 to N.
Step 2: Let k be the nearest integer less than N/n.
Step 3: Select the random start r, where 1 ≤ 𝑟 ≤ 𝑁. The unit corresponding to r is the first unit of the sample.
Step 4: Consider the list of units of the population as a circular list, i.e., the last unit in the list is followed by the first. The other units in the sample are the units corresponding to r + k, r + 2k, r + 3k,…, r+ (n-1)k.
the population of N units is first divided into subpopulations called strata. Then a simple random sample is drawn from each stratum, the selection being made independently in different strata.
Stratified random sampling
Explain the process of stratified random sampling
Step 1: Divide the population into strata. Ideally, each stratum must consist of more or less homogeneous units.
Step 2: After the population has been stratified, a simple random sample is selected from each stratum.
A common strategy is to select a number of units from each stratum that is proportional to the number of sample units (or size) within each stratum
proportional allocation
method of sampling where a sample of distinct groups, or clusters, of elements is selected and then a census of every element in the selected clusters is taken.
Cluster sampling
Explain the process of cluster sampling
Step 1: Number the clusters from 1 to N.
Step 2: Select n numbers from 1 to N at random. The clusters corresponding to the selected numbers form the sample of clusters.
Step 3: Observe all the elements in the sample of clusters.
- the population is divided into a hierarchy of sampling units corresponding to the different sampling stages. In the first stage of sampling, the population is divided into primary stage units (PSU) then a sample of PSUs is drawn.
- In the second stage of sampling, each selected PSU is subdivided into second-stage units (SSU) then a sample of SSUs is drawn.
Multistage sampling
