Census

Sampling

Observational study

Experiment

Methods of Data Collection

Methods of Data Collection

- obtains data from EVERY member of a population

- Survey of the WHOLE population

- Census data are commonly used for research, business marketing, and planning, as well as a baseline for sampling surveys

1. CENSUS

CENSUS

1. Preparation Work

2. Enumeration of Field Work

3. Post-enumeration Work

Phases of the census operation

Methods of Data Collection

- obtains data from a subset of a population, in order to estimate population attributes- Obtain a representative sample of the population

- e.g., Online surveys, Poll surveys, Popularity ratings

2. Sampling

Methods of Data Collection

3. Observational study - Basically, a researcher goes out into the world and looks for variables that are associated with one another

EXAMPLE: Charles Darwin based his explanation of evolution entirely on observations he made- The researcher do not determine which subjects are to be in control and which is treatment.

EXAMPLE: In a study on smoking, the SMOKERS form the treatment group and the NONSMOKERS are the control group

Observational Study

A control group is a baseline group that receives no treatment or a neutral treatment. For example, when examining test tubes for catalytic reactions of enzymes when added to a specific substrate, the control test tube would be identical to all other test tubes with the exception of lacking the enzyme.

The treatment group is the item or subject that is manipulated.

Observational Study

ADVANTAGES• They put the researcher

directly in touch with the behaviors in question

• They involved real-time data, describing behavior occurring in the present rather than the past

• They are adapting in that they can be modified depending on what is being observed

DISADVANTAGES• Difficulties interpreting the

meaning underlying the observations.

• Observers must decide which to observe; choose time periods, territory and events

Methods of Data Collection

4. Experiment

- the researcher controls: a) how subjects are assigned to groups b) which treatments each group receives

- a scientific test carried out in order to discover whether a theory or hypothesis is correct or what the results of a particular course of action would be- most clearly shows cause-and-effect because it isolates and manipulates a single variable, in order to clearly show its effect

Experiment

Types of ExperimentA. CONTROLLED- generally compares the results obtained from an

experimental sample against a control sample

The sample or group

receiving the drug

The one receivin

g the placebo

Control GroupTreatment/

Experimental

Group

EXAMPLE: A Drug Trial

Experiment

Types of ExperimentB. NATURAL OR QUASI-EXPERIMENTS - relies solely on observations of the

variables of the system under study

Nuclear weapons testing released large quantities of radioactive isotopes into the atmosphere, some of which could be incorporated into biological tissues. - The release stopped after the Partial Nuclear Test Ban Treaty in 1963, which prohibited atmospheric nuclear tests. This resembled a large-scale pulse-

chase experiment, but could not have been performed as a regular experiment in humans due to scientific ethics. - Several types of observations were made possible (in people born before 1963), such as determination of the rate of replacement for cells in different human tissues.

Experiment

Types of ExperimentC. FIELD EXPERIMENTS - outcomes are observed in a natural setting rather than in an unnatural laboratory environment

- generally randomize subjects (or other sampling units) into treatment and control groups and compare outcomes between these groups.

Examples:• Clinical trials of pharmaceuticals are one example of

field experiments.• Economists have used field experiments to analyze

discrimination, health care programs, charitable fundraising, education, information aggregation in markets, and microfinance programs.

• Engineers often conduct field tests of prototype products to validate earlier laboratory tests and to obtain broader feedback.

Pros and Cons• Resources. When the population is large, a sample survey

has a big resource advantage over a census. A well-designed sample survey can provide very precise estimates of population parameters - quicker, cheaper, and with less manpower than a census.

• Generalizability. If participants in a study are randomly selected from a larger population, it is appropriate to generalize study results to the larger population; if not, it is not appropriate to generalize. Observational studies do not feature random selection; so generalizing from the results of an observational study to a larger population can be a problem.

• Causal inference. Experiments, which allow the researcher to control assignment of subjects to treatment groups, are the best method for investigating causal relationships.

REFERENCEShttp://en.wikibooks.orghttp://images.google.comhttp://en.wikipedia.orghttp://stattrek.comhttp://www.ncsu.eduElementary Statistics, Neil A. Weiss, Addison-Wesley Publishing Company, 1989Microsoft® Encarta® 2009. © 1993-2008 Microsoft Corporation.