Experimental and Quasi-Experimental Design
Use these abbreviations: • A • X • O &B Subjects Treatment Observation
� A O � B O X O O
� A O � B O X(1) X(2) O O
� Non-Experimental � Groups or Quasi-Experimental are not equivalent (not random)
Example This study was designed to compare the efficacy of two methods on accuracy of multiplication of five students with learning disabilities. During oral recitation, the students orally answered the problems presented by the experimenter. The other method was similar except that the students were required to write the answer after hearing the problem. Results showed that all students achieved higher accuracy with the oral answers method.
� Is this experimental or non-experimental? � Is it qualitative or quantitative? � What are the variables? � Design?
Stratified Random Sampling
Systematic Random Sampling
Cluster Random Sampling Choose only the people who live In the Red “clusters”
Nonprobability Sampling � Purposive Sampling – Purposively choose people who will be good examples � Convenience Sampling- Use a pre-formed group (such as a class) � Quota Sampling – like Stratified except it is not random � Snowball sampling – Find 1 candidate and have him recommend another and so on…
Selection Bias � This occurs when some members of the population are inadequately represented in the sample. � A classic example is the Literary Digest voter survey, which predicted that Alfred Landon would beat Franklin Roosevelt in the 1936 presidential election. The survey sample suffered because they did not survey low-income voters, who tended to be Democrats.
How did this happen? � The survey relied on a convenience sample, drawn from telephone directories and car registration lists. In 1936, people who owned cars and telephones tended to be more affluent.
Non-Response bias � Non-response bias occurs when individuals chosen for the sample are unwilling or unable to participate in the survey. � The Literary Digest experience illustrates a common problem with mail surveys. Response rate is often low, making mail surveys vulnerable to non-response bias.
Voluntary Response Bias � Voluntary response bias occurs when sample members are self-selected volunteers, as in voluntary samples. An example would be call -in radio shows that solicit audience participation in surveys on controversial topics (abortion, affirmative action, gun control, etc. ). The resulting sample tends to over represent individuals who have strong opinions.
Leading questions � The wording of the question may be loaded in some way to unduly favor one response over another. For example, a satisfaction survey may ask the respondent to indicate where she is satisfied, dissatisfied, or very dissatisfied. By giving the respondent one response option to express satisfaction and two response options to express dissatisfaction, this survey question is biased toward getting a dissatisfied response.
Social desirability � Most people like to present themselves in a favorable light, so they will be reluctant to admit to unsavory attitudes or illegal activities in a survey, particularly if survey results are not confidential. Instead, their responses may be biased toward what they believe is socially desirable.
Sampling Distribution �A survey produces a sample statistic, which is used to estimate a population parameter. If you repeated a survey many times, using different samples each time, you would get a different sample statistic with each replication. And each of the different sample statistics would be an estimate for the same population parameter.
Instrumentation � Blind � Double Blind � Tests: ◦ Norm Referenced – individuals are scored against a “Norm” ◦ Criterion Referenced – independent of anyone else who takes the test. Does this student meet expectations.
Types of Tests � Achievement Tests � Aptitude Tests � Intelligence Tests � Likert Scale Tests/Questionnaires � Interviews � Unobtrusive Methods � Observations