In longitudinal education studies, assuming that dropout and missing data occur completely at random is often unrealistic. When the probability of dropout depends on covariates and observed responses (called "missing at random" [MAR]), or on values of responses that are missing (called "informative" or "not missing at random" [NMAR]),…

Because random assignment is not possible in observational studies, estimates of treatment effects might be biased due to selection on observable and unobservable variables. To strengthen causal inference in longitudinal observational studies of multiple treatments, we present 4 latent growth models for propensity score matched groups, and…

The Statistics Online Computational Resource (http://www.SOCR.ucla.edu) provides one of the largest collections of free Internet-based resources for probability and statistics education. SOCR develops, validates and disseminates two core types of materials--instructional resources and computational libraries. (Contains 2 figures.)

In demand paging virtual memory systems, the page fault rate of a process varies with the number of memory frames allocated to the process. When an increase in the number of allocated frames leads to an increase in the number of page faults, Belady's anomaly is said to occur. In this paper, we present a probability model for Belady's anomaly. We…

Congenital amusia is a neurogenetic disorder that affects the processing of musical pitch in speakers of non-tonal languages like English and French. We assessed whether this musical disorder exists among speakers of Mandarin Chinese who use pitch to alter the meaning of words. Using the Montreal Battery of Evaluation of Amusia, we tested 117…

On the 2009 AP[c] Statistics Exam, students were asked to create a statistic to measure skewness in a distribution. This paper explores several of the most popular student responses and evaluates which statistic performs best when sampling from various skewed populations. (Contains 8 figures, 3 tables, and 4 footnotes.)

This is a critical review of surveys conducted on the American deaf population since 1990. There is no agreement among the surveys on the number of deaf and hard of hearing individuals in the US. This behooves us to study the question: Why the lack of agreement in estimates and prevalence rates of the American general deaf and the deaf child…

Propensity score methods allow investigators to estimate causal treatment effects using observational or nonrandomized data. In this article we provide a practical illustration of the appropriate steps in conducting propensity score analyses. For illustrative purposes, we use a sample of current smokers who were discharged alive after being…

Uniformity, that is, equiprobability of all available options is central as a theoretical presupposition and as a computational tool in probability theory. It is justified only when applied to an appropriate sample space. In five studies, we posed diversified problems that called for "unequal" probabilities or weights to be assigned to the given…

In operational equating, frequency estimation (FE) equipercentile equating is often excluded from consideration when the old and new groups have a large ability difference. This convention may, in some instances, cause the exclusion of one competitive equating method from the set of methods under consideration. In this report, we study the…

In this paper, we present an analysis of the Arkansas Teacher Retirement System (ATRS) pension plan and an empirical investigation of the behavioral response to that plan, as well as to a possible reform plan. We begin by describing the plan parameters and discussing the incentives these parameters create. We then estimate the effect of pension…

Community participation in planning and managing for increased educational opportunity is necessary. To ensure the involvement of local community, the government of Pakistan experimentally launched a scheme in 1994 by establishing School Management Committees (S.M.Cs). The major purpose of the present study was to observe the functions and…

The acquisition of volitional control depends, in part, on developing the ability to countermand a planned action. Many tasks have been used to tap the efficiency of this process, but few studies have investigated how it may be modulated by participants' motivation. Multiple mechanisms may be involved in the deliberate exercise of caution when…

Concepts in probability can be more readily understood if students are first exposed to probability via experiment. Performing probability experiments encourages students to develop understandings of probability grounded in real events, as opposed to merely computing answers based on formulae.

This article examines some of the various judgmental errors and rationales that high school students make when attempting to solve basic probability exercises. Many of these errors allow the students to arrive at a correct answer and, thus, need to be examined more closely. (Contains 4 tables.)