Quantitative Analysis

Part 1

Compare and contrast internal and external validity. Describe and give

examples of research questions for which external validity is a primary

concern. Describe and give examples of research questions in which

internal validity is a primary concern. Discuss strategies researchers

use in order to make strong claims about the applicability of their

findings to a target population.

Compare and contrast random selection and random assignment. Be sure to

include a discussion of when you would want to do one or the other and

the possible consequences of failing to do random selection or random

assignment in particular situations.

Explain the relationship between sample size and the likelihood of a

statistically significant difference between measured values of two

groups. In other words, explain why, all else being equal, as sample

size increases the likelihood of finding a statistically significant

relationship increases.

Compare and contrast probability and non-probability sampling. What are

the advantages and disadvantages of each?

Part 2

If you do a quantitative study for your dissertation, you must estimate

the sample size you will need in order to have a reasonable chance of

finding a relationship among the variables stated in your research

hypotheses (should one exist), given your statistical analysis(es) and

assumptions/calculations of factors 2-4 above. You must do this, even if

you plan to use a convenience sample (see below). There are a number of

sample size calculators available. Northcentral uses G*Power, which is

required in this Activity. You will use G*Power’s “a priori power

analysis” function to calculate a sample size. If it yields an

unrealistically large size sample, you will rethink your design and

assumptions and, perhaps, use G*Power’s “compromise power analysis” to

estimate a workable sample size that makes sense. If you plan on using a

convenience sample, you would use both analyses as part of your argument

that your convenience sample is large enough.

Main Task: Submit the Following

1.

Calculate the sample size needed given these factors:

one-tailed t-test with two independent groups of equal size

small effect size (see Piasta, S.B., & Justice, L.M., 2010)

alpha =.05

beta = .2

Assume that the result is a sample size beyond what you can obtain. Use

the compromise function to compute alpha and beta for a sample half the

size. Indicate the resulting alpha and beta. Present an argument that

your study is worth doing with the smaller sample.

2.

Calculate the sample size needed given these factors:

ANOVA (fixed effects, omnibus, one-way)

small effect size

alpha =.05

beta = .2

3 groups

Assume that the result is a sample size beyond what you can obtain. Use

the compromise function to compute alpha and beta for a sample

approximately half the size. Give your rationale for your selected

beta/alpha ratio. Indicate the resulting alpha and beta. Give an

argument that your study is worth doing with the smaller sample.

3. In a few sentences, describe two designs that can address your

research question. The designs must involve two different statistical

analyses. For each design, specify and justify each of the four factors

and calculate the estimated sample size you’ll need. Give reasons for

any parameters you need to specify for G*Power.

Include peer-reviewed journal articles as needed to support your

responses to Part I.

Support your paper with a minimum of 5 resources. In addition to these

specified resources, other appropriate scholarly resources, including

older articles, may be included.

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