Dissertation control groups

Dissertation control groups

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What is Effect Size and Why Does It Matter?

Federal government websites often end in. gov or. The site is secure, dissertation control groups. This report was prepared under contract HHS between the U. Department of Health and Human Services HHSOffice of Social Services Policy now the Office of Disability, Aging and Long-Term Care Policy and Mathematica Policy Dissertation control groups, Inc.

Additional work on this project was conducted by Temple University. Humphrey Building, Independence Avenue, S. The e-mail address is: webmaster. DALTCP hhs. The Project Officer was Robert Clark. This paper represents work in progress and is not to be cited without the permission of the author.

This report was prepared for the Department of Health and Human Services under contract no. The Department of Health and Human Services project officer is Mr, dissertation control groups. Robert Clark, Office of the Secretary, Department of Health and Human Services, Room F, Hubert Humphrey Building, Washington, D. Throughout the design and implementation of the channeling demonstration, emphasis has been placed on the importance of random assignment of eligible applicants into treatment and control groups.

Due to the random assignment, the resulting control and treatment groups should be composed of eligible individuals that on average are very similar at the time of application on any observed or unobserved characteristic. This lack of pre-existing differences between treatments and controls implies that the control group yields reliable estimates of what would have happened to clients in the absence of channeling, and when these estimates are compared to outcomes for clients, reliable estimates of channeling impacts are obtained.

Only two factors can lead to differences in the true mean values of the pre-application characteristics of the treatment and control groups: deviation from the randomization procedures and normal sampling variability. Deviations from the carefully developed randomization procedures could be either deliberate e. The dedication and professionalism of this site staff and the safeguards built into the assignment procedure make either occurrence very unlikely.

Site staff were extremely cooperative in faithfully executing the procedures. Sampling variability, on the other hand, is the difference between the two groups that occurs simply by chance. For the sample sizes available at the model level, such differences between the two groups should be very small, dissertation control groups, and statistically insignificant. For example, dissertation control groups, if we find that the treatment group was more severely impaired at the time the screen was given, differences between the two groups in mean impairment level six months after randomization would reflect both initial differences and the effects of channeling.

The relationship may also be more subtle. For example, if channeling were more effective for certain subgroups than for others e. Regression procedures can help to control for initial differences such as these, but there is no guarantee that the variables available to include in the regression will control for all of the factors which are differentially represented in the two groups and which affect the post-randomization values of outcome variables.

Furthermore, the appropriate relationship may not be linear, as would typically be assumed in regression. Thus, one of the primary virtues of experimental design, the ability to rely on simple, dissertation control groups, robust comparisons of treatment and control group means to obtain unbiased estimates of program impacts, is lost if treatment and control groups are not equivalent at the time of randomization.

Unbiasedness is then dependent upon assumptions about the correctness of the regression specification i. The comparability of the treatment and control groups at randomization is also important because it is the first stage in our investigation of a set of methodological problems that could result in biased estimates of channeling's impact.

Differences between treatment and control groups in dissertation control groups types of individuals who fail to respond to interviews could result in noncomparable groups in the sample being analyzed, even if the full samples were comparable. Differences in the way baseline data were collected for treatments and controls could lead to differential measurement error, dissertation control groups, which could cause regression estimates of program impacts to -be biased, dissertation control groups.

In order to assess these other potential sources of bias, it is important to first determine whether the two groups were comparable before the baseline interview. Because of these goals and concerns, in this paper we assess the equivalence of the treatment and control groups at the time of randomization by comparing the screen characteristics of the two groups.

The data collected at the screen do not provide an ideal basis for the comparison in that differences between treatments and controls in the extent of item nonresponse and differences in the accuracy of the screen data ultimately recorded could lead to differences in the computed means at the screen, even if the two groups are comparable.

However, these dissertation control groups did not seem to occur, and in any case are much less significant than the problems of interpretation that would be caused by using baseline data to assess comparability of the two groups. The differences between the two groups in baseline data collection procedures and interview nonresponse are potential problems with that interview that are not problems with the screen. If our analysis of comparability of the two groups using screen data indicates no differences between the treatment and control groups, then comparisons of their data at baseline can be conducted to assess the issues of nonresponse and measurement bias described above, dissertation control groups.

If preenrollment differences between the dissertation control groups groups are found, dissertation control groups, then these differences must be controlled for in the other methodological investigations. Section I contains descriptions of the screen data used for this analysis, and the randomization process employed to assign treatment status to eligible elders expressing potential interest in channeling. Section II contains a description of the statistical tests performed and the results of these tests.

The emphasis is on comparisons between treatment and control groups at the model level; however, site-specific comparisons are also examined, dissertation control groups. Section III concludes the paper, indicating the implications of the results for the analysis of channeling impacts.

The source and nature of the screen data on dissertation control groups this analysis is based are discussed below, and sample sizes are indicated. This is followed by a dissertation control groups description of the randomization dissertation control groups. The screening instrument was developed to identify those elderly individuals who were at high risk of nursing home placement those who in the absence of channeling would be in an institution.

A set of objective criteria were established that were felt would distinguish such individuals, dissertation control groups. Data collected from the screen were used dissertation control groups establish whether a given applicant satisfied these criteria and should therefore be classified as eligible. The criteria incorporated the following dimensions: severe functional impairment; expected unmet need in two service categories e. for six months or more, or expected lack of sufficient help from family and friends in the coming months; residence in the community or, if institutionalized, certified as likely to be discharged into a noninstitutional setting within three months; residence within the project's geographical boundaries; age; and for financial control sites only Medicare Part A eligibility.

The screening instrument was designed for a short telephone interview, to be administered in dissertation control groups uniform manner by each of the 10 demonstration projects, dissertation control groups. The telephone screening process was intended to reduce the cost of determining appropriateness for channeling compared to using a comprehensive in-person assessment for that purpose. Channeling project staff who conducted the screening interviews were in a separate administrative unit from assessment and case management staff.

This was required chiefly to preserve the integrity of the experimental design--the potential for influencing the behavior of persons assigned to the control groups through contact with channeling staff was minimized by this administrative separation.

Applicants for channeling services came to the attention of the screening unit primarily in two ways: elderly individuals or family, friends, clergy, neighbors, or other persons acting on their behalf contacted the screening unit directly, or formal provider organizations contacted channeling to make a referral.

Hospitals, home health agencies, senior centers, and nursing homes were among the formal referral sources. Screeners were instructed to conduct the interview directly with potential clients where possible, but could also accept reports from formal referral sources, families, friends, and other proxies.

Projects imposed guidelines of generally no more than 72 hours from referral to screen completion although it was not always possible to meet these guidelines. Most screens were conducted by telephone, dissertation control groups, but in a very small proportion of the cases in-person screens were performed instead. Major reasons reported dissertation control groups the use of in-person screens included applicants who had hearing impairments, difficulty understanding the project, or no access to telephones.

The analysis presented here is based on the screen data for 6, research sample observations treatments and controls see Table 1. Those who enrolled either before or after the March to June period 2 during which randomization of eligible applicants occurred are not included in this analysis, nor are individuals residing in the same household as a previously assigned sample member.

A small number of eligible applicants 15 control group members are excluded because their screening instruments were lost in the mail. After the screen was completed, eligible applicants were randomly assigned to either the treatment or the control group. The randomization process was designed to be as error-free and easy to implement as possible. A random number generator was used to create a string of ones and zeroes for each site, dissertation control groups, designating treatment and control status, respectively.

The process is summarized below:. This information was then read back or spelled, as necessary, by the MPR clerk to ensure that it was recorded accurately. This structured process leaves little room for error or ambiguity and has worked well throughout the course of the project. Although three instances of misrecorded treatment status were discovered, dissertation control groups, 5 no general problems with these procedures were encountered that could compromise the integrity of the experimental design.

Thus, the procedures used are not likely to result in differences between the treatment and control groups. Only empirical analysis of the data, as discussed below, can reveal whether either sampling error or procedural mistakes have produced non-equivalent treatment and control groups, dissertation control groups. To assess whether the treatment and control groups created by the randomization procedures were equivalent at the time of randomization, variables describing the characteristics of the sample members were constructed from the screen data, dissertation control groups.

Mean values of these variables were obtained for treatment and control groups at each site and a standard statistical test of the difference between these means 7 was conducted. This statistical test provides us with an indication of whether any observed differences between the two groups on average should be considered "large" relative to what would be expected as the result of chance sampling variability. If the difference between the means is so great that randomly drawn samples would produce a difference that large fewer than one time in 10, we may not be very confident that the two groups being compared are alike enough that mean outcomes for the control group can be assumed to dissertation control groups a good indication of what would have happened to treatments in the absence of channeling.

For screen values of outcome variables, such as ability to perform activities of daily living ADLstatistical significance of differences is also important because they imply that even if channeling had no impact at all, a comparison of treatment and control group means on ADL at six months after randomization would appear to indicate that channeling had had a statistically significant impact, because the difference in initial values would also be reflected in the values at six months.

Statistically significant differences will occur by chance, dissertation control groups when many different variables are being examined, dissertation control groups. However, the differences are not expected to be pervasive or large.

Mean values of variables for the treatment and control, groups could be computed and dated for statistically significant differences at the model level; however, the results could be very misleading, dissertation control groups.

This is because dissertation control groups ratio of treatment to control group members is different in different sites, 8 ranging from about in the larger sites to in the smaller sites. Simple means at the model level for each group are equal to a weighted average of the five site means for the group, with the weight for each site being the proportion of observations for the group which come from that site.

Thus, in estimating the model level mean for the treatment group, the treatment group mean at a site will have a larger weight than will the corresponding site control group mean in estimating the dissertation control groups level mean for controls.

This different weight applied to treatment and control groups from a given site can lead to anomalous results and can eliminate the very advantages that a randomized design offers. Suppose further that 25 percent of dissertation control groups treatment group came from Site A but only 15 percent of the control group did.

This would result in a treatment group mean at the model level that was lower than the control group mean, dissertation control groups, simply because the site with low ADL comprised a greater proportion of the treatment group, and in spite of the fact that the randomization process produced equivalent treatment and control groups in every site.

What is required is a procedure that preserves the equivalence of the two groups in comparisons at the model level. That is, the estimated model-level difference between treatments and controls should be a weighted average of the site-level difference. An attractive choice for a set of weights would be one in which the site differences that were measured most precisely received the largest weights. That is the procedure implemented in this report. In practice, this weighted average is obtained by regressing each variable being examined e.

The weight for the i th site is: 9. where r i is the proportion dissertation control groups observations from the i th site that belong to the treatment group. Standard errors and t-statistics of these estimates are readily obtained from the computer printout, dissertation control groups. These estimates and test statistics are presented below for screen data on a variety of variables, dissertation control groups.

Treatment group means are also presented for reference, dissertation control groups. Results are presented for the model level differences followed by a brief discussion of site-specific differences in means. The screen contains data on respondents' demographic characteristics, financial resources, living arrangement, health and functioning, help received, and referral source.

Dissertation Webinar Series Session 3: Methodology \u0026 IRB/URR

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Dissertation Control Groups - What is a Control Group? - Definition and Use in Research

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