Correlated Errors

Top PDF Correlated Errors:

Markov Properties for Linear Causal Models with Correlated Errors

Markov Properties for Linear Causal Models with Correlated Errors

A linear causal model with correlated errors, represented by a DAG with bi-directed edges, can be tested by the set of conditional independence relations implied by the model. A global Markov property specifies, by the d-separation criterion, the set of all conditional independence relations holding in any model associated with a graph. A local Markov property specifies a much smaller set of conditional independence relations which will imply all other conditional independence relations which hold under the global Markov property. For DAGs with bi-directed edges associated with arbitrary probability distributions, a local Markov property is given in Richardson (2003) which may invoke an exponential number of conditional independencies. In this paper, we show that for a class of linear structural equation models with correlated errors, there is a local Markov property which will invoke only a linear number of conditional independence relations. For general linear models, we provide a local Markov property that often invokes far fewer conditional independencies than that in Richardson (2003). The results have applications in testing linear structural equation models with correlated errors.

30 Read more

Kernel Regression in the Presence of Correlated Errors

Kernel Regression in the Presence of Correlated Errors

It is a well-known problem that obtaining a correct bandwidth and/or smoothing parameter in non- parametric regression is difficult in the presence of correlated errors. There exist a wide variety of methods coping with this problem, but they all critically depend on a tuning procedure which requires accurate information about the correlation structure. We propose a bandwidth selection procedure based on bimodal kernels which successfully removes the correlation without requiring any prior knowledge about its structure and its parameters. Further, we show that the form of the kernel is very important when errors are correlated which is in contrast to the independent and iden- tically distributed (i.i.d.) case. Finally, some extensions are proposed to use the proposed criterion in support vector machines and least squares support vector machines for regression.

22 Read more

Computing Maximum Likelihood Estimates in Recursive Linear Models with Correlated Errors

Computing Maximum Likelihood Estimates in Recursive Linear Models with Correlated Errors

The requirement of uncorrelated errors may be overly restrictive in many settings. While arbitrary correlation patterns over the errors may yield rather ill-behaved statistical models, there are sub- classes of models with correlated errors in which some of the nice properties of DAG models are preserved; compare McDonald (2002). In this paper we consider path diagrams in which there are no directed cycles and no ‘double’ edges of the form i → ↔ j (compare Def. 2 and 3). Since such double edges have been called ‘bows’, we call this class bow-free acyclic path diagrams (BAPs). An example of a BAP arose in our motivating example in §1.1; see Figure 1. While instrumental variable models, which are much studied in economics, contain bows, most models in other social sciences are based on BAPs. For instance, all path diagrams in Bollen (1989) are BAPs.

20 Read more

On the Local Power of Fixed T Panel Unit Root Tests with Serially Correlated Errors

On the Local Power of Fixed T Panel Unit Root Tests with Serially Correlated Errors

The original WG and IV tests allow for heterogeneous disturbances across i but this assumption is trimmed so that tractable results may be obtained. For the same reasons, normal errors provide analytic formulas for the variances of the tests. Condition (1.1) ensures the existence of at least one moment condition free of correlation nuisance parameters but does not specify the true order of serial correlation. De…ne p the order of serial correlation assumed by the researcher and p the true order. As long as p p the limiting distribution of the test statistics is valid. Since inference in both tests is based on moments that are free of correlation parameters, choosing p > p means selecting fewer than possible moments for inference. For a discussion on how to estimate the order of serial correlation see Hayakawa (2010).

42 Read more

Efficiency Comparisons of Different Estimators for Panel Data Models with Serially Correlated Errors: A Stochastic Parameter Regression Approach

Efficiency Comparisons of Different Estimators for Panel Data Models with Serially Correlated Errors: A Stochastic Parameter Regression Approach

Abstract: This paper considers panel data models when the errors are first-order serially correlated as well as with stochastic regression parameters. The generalized least squares (GLS) estimators for these models have been derived and examined in this paper. Moreover, an alternative estimator for GLS estimators in small samples has been proposed, this estimator is called simple mean group (SMG). The efficiency comparisons for GLS and SMG estimators have been carried out. The Monte Carlo studies indicate that SMG estimator is more reliable in most situations than the GLS estimators, especially when the model includes one or more non-stochastic parameter.

15 Read more

New evidence of factor structure and measurement invariance of the SDQ across five European nations

New evidence of factor structure and measurement invariance of the SDQ across five European nations

The study of the internal structure, by means of CFAs, supported the five-factor structure in all the countries and in the total sample, as it is the case in previous studies [40,27,11,24,28,29,25]. Nevertheless, adequate goodness-of-fit indices were found after adding error correlation between items, indicating discrete values in the five-factor baseline model in all the countries. Moreover, some goodness-of-fit indices of Ireland were still not appropriate. Similar results were found in previous studies [40,32,19,26]. For instance, the study of Ortuño-Sierra et al. [40] showed that the five-factor structure was the better to fit the data, but appropriate goodness-of-fit were only reached after correlated errors were added. Thus, the five-factor structure is still questionable. In the same line, a modified five factor model allowing the reverse-worded items to cross-load on the Prosocial factor displayed significant better goodness-of-fit indices in all the countries, including the total sample, as it was the case in the study of van de Looij–Jansen et al. [26]. However, the study of factor loadings revealed that some of them were non-significant, questioning the adequacy of this model.

27 Read more

Measuring mental well being in Norway: validation of the Warwick Edinburgh Mental Well being Scale (WEMWBS)

Measuring mental well being in Norway: validation of the Warwick Edinburgh Mental Well being Scale (WEMWBS)

Measurement invariance was examined separately for gender (male vs female), and equal sized age groups (18–30; 31–43; ≥44). First, configural invariance was tested by estimating the 1-factor model of the WEMWBS in each group without constraining factor loadings and intercepts. In the next step, metric invari- ance was tested by constraining the factor loadings to be equal in each group. Due to the categorical nature of the indicators, additional constraints were required to test metric invariance; the first threshold of each item was held equal across groups and the second threshold of the item that was used to set the metric of the factor was also held equal across groups [42]. Finally, both factor loadings and thresholds were constrained to be equal across groups to test for scalar invariance. Scalar invariance is required for comparing absolute scores across groups. In many cases, full scalar invariance cannot be obtained and one or more of the constrained model parameters need to be set free in order to improve model fit. According to recommendations from Byrne et al. [43] partial scalar invariance is obtained when at least two of the factor indicators are invariant. Testing strict measure- ment invariance, in which residual variances are fixed to one across groups, was considered less relevant for the present study since correlated errors were explicitly accounted for in the measurement model [44]. Adjust- ments to the model were informed by SEPC. In line with Cheung and Rensvold [45], we used a change in CFI of more than 0.01 as an indicator of true difference in relative model fit.

9 Read more

Using message logs and resource use data for cluster failure diagnosis

Using message logs and resource use data for cluster failure diagnosis

We presented the CRUMEL framework that correlated both the message logs and resource use data to identify errors and resource usage patterns. We showed that the new approach to integration of resource use data and message logs, and the use of multiple correlation algorithms can identify more events associated with system failures. The framework confirmed six groups of errors, identified Lustre I/O resource use counters that are correlated with occurrence of Lustre faults that are potential flags for online detection of failures, matched the dates when correlated errors and correlated resource use counters are associated with the dates of compute node hang- ups, and identified two more error groups - process errors and file-system errors - associated with compute node hang-ups.

11 Read more

A New Method of Construction of Robust Second Order Rotatable Designs Using Balanced Incomplete Block Designs

A New Method of Construction of Robust Second Order Rotatable Designs Using Balanced Incomplete Block Designs

Das [1,2] studied robust second order rotatable designs (RSORD) and constructed second order rotatable designs with correlated errors (SORDWCE) under the auto correlated structure using central composite design. In this paper, a new method of construction of RSORD using balanced incomplete block designs (BIBD) is suggested. In this method the number of design points required is in some cases less than the number required in Das [1,2] method of construction of robust rotatable central composite designs (RRCCD). We may point out here that this RSORD using BIBD has 113 design points for 7-factors where as the corresponding RRCCD obtained by Rajyalakshmi and Victorbabu [3] needs 157 design points. Thus the new method leads to a 7-factor RSORD in less number of design points than the corre- sponding RRCCD. Here we also obtained the variance of the estimated response for the factors 3 ≤ v ≤ 8.

9 Read more

Pharmacist's Intervention and Medication Errors Prevention at Pediatrics, Obstetrics and Gynecology Hospital in East Province, Saudi Arabia

Pharmacist's Intervention and Medication Errors Prevention at Pediatrics, Obstetrics and Gynecology Hospital in East Province, Saudi Arabia

reduce the medication errors and prevent harms from reaching the patients. It can be reached through building safer organization endlessly improve its quality. The medication safety manual, which is considered as the foundation of the program, was the first step to be formulated to serve as guide for MOH organizations. There are medication safety officers, as well as there is a committee to medication safety in both the hospitals, primary health care and the Committee for each region as well as the main committee meets monthly in the ministry’s pharmaceutical care administration. For the eastern region, there are 10 hospitals containing medication safety officer, medication safety committee, ISMP medication safety for hospitals in 2014, medication safety committee in the region to analyze the study to develop plans and prevent their reoccurrence. In 2015, basic medication safety course was started in maternity children hospital, Dammam, where 42 nurses, 9 doctors and 7 pharmacists were the highest attendees. Medication error is an essential variable to determine patient safety services, so it is crucial to realize the weak points of health care members regarding medication error and provide an educational program to resolve them.

7 Read more

A Review on Medication Errors

A Review on Medication Errors

Abstract: Role of clinical pharmacist is to provide optimal pharmaceutical care for individual patients and optimal pharmaceutical care is attained when the right drug in the correct dosage and quality reaches the right patients at the right point in time with the right information. Any preventable event that may cause or lead to inappropriate medication use or patient harm during medication to user is called medicational error and is in the control of the health care professional, patient and consumer. In this review on medication errors, prescr - ibing errors (67 %), administration errors (25%), dispensing errors (08%) were found on the basis of review of literature. Prescribing errors are the prime cause of MEs that further leads to subsequent dispensing and administration errors. Medication errors are common cause of adverse drug events or subtherapeutic outcomes of pharmaceutical care.

8 Read more

A Comparison of MT Errors and ESL Errors

A Comparison of MT Errors and ESL Errors

students than to low-performing MT systems. Comparing the error distributions of the eight MT sys- tems, we observe that all eight MT systems have fairly similar distributions regardless of their source languages. Moreover, the four high-performing MT systems have er- ror distribution that are more similar to those of the low- performing MT systems than to those of ESL learners with the same L1. Thus, the results suggest that our two hy- potheses do not hold. However, it is also not the case that the source language has no impact on the performance of the systems. For example, consider the German-English case. Comparing to other ESL students, German students make a significant amount of punctuation mistakes (51%). In a more subdued fashion, the low-performing German- English MT system makes more punctuation errors than the high-performing system. In contrast, for the other lan- guages the low and high-performing machine translation systems make similar proportions of punctuation mistakes. There are two possible explanations for why the error dis- tribution patterns of MT systems behaved differently than what we hypothesized. One is that the MT systems have largely the same underlying model – they are statistical phrase-based systems. They use the same English language model; therefore, they have similar preferences in terms of the fluency of the output sentences. Another possibility is that because MT systems are still struggling with word choice decisions, which is an adequacy problem, their dis- tribution of errors is skewed by the high word choice errors, which are mostly due to unaligned words in the reference and MT output sentences. In contrast, the focus of the ESL error categories is on fluency problems only. To factor out the impact of word choice error, we examine article errors in greater detail.

5 Read more

An adapted version of the element wise weighted total least squares method for applications in chemometrics

An adapted version of the element wise weighted total least squares method for applications in chemometrics

The Maximum Likelihood PCA (MLPCA) method has been devised in chemometrics as a generalization of the well-known PCA method in order to derive consistent estimators in the presence of errors with known error distribution. For similar reasons, the Total Least Squares (TLS) method has been generalized in the field of computational mathematics and engineering to maintain consistency of the parameter estimates in linear models with measurement errors of known distribution. In a previous paper [M. Schuermans, I. Markovsky, P.D. Wentzell, S. Van Huffel, On the equivalance between total least squares and maximum likelihood PCA, Anal. Chim. Acta, 544 (2005), 254 – 267], the tight equivalences between MLPCA and Element-wise Weighted TLS (EW-TLS) have been explored. The purpose of this paper is to adapt the EW-TLS method in order to make it useful for problems in chemometrics. We will present a computationally efficient algorithm and compare this algorithm with the standard EW-TLS algorithm and the MLPCA algorithm in computation time and convergence behaviour on chemical data.

7 Read more

Accurate Determination of GPS Receiver with Different Classification Methods

Accurate Determination of GPS Receiver with Different Classification Methods

Nowadays localization has become an important necessity in life. One of the best methods for estimation of position is Global Positioning System (GPS). GPS receivers can estimate position, velocity and time. GPS position errors are determined by pseudo-range errors and satellite geometry. The main pseudo-range measurements errors can be divided into three groups: ephemeris errors and satellite clock errors, atmospheric errors, and user receiver errors (frequency drift, pseudo- noise sequence phase drift, and signal detection time). Ephemeris errors and satellite clock errors occur when the GPS message does not transmit the correct satellite location. With the use of measurements of pseudo- ranges on two frequencies, the ionospheric amendment (correction) of measurements of pseudo-range on a C/A code for ground receivers is determined. After obtaining the pseudo-range and Doppler frequency measurements errors connected to stability of a frequency generator, the stability of pseudo-noise sequence phase drift and stability signal detection time, are called by various synchronization of user's receiver time and GPS-system. The dynamics of an oscillator of receiver frequency generator and pseudo-noise sequence phase drift and accuracy of signal detection time is investigated [1].

10 Read more

Need for Re - Engineering Quality Assurance in Clinical trials

Need for Re - Engineering Quality Assurance in Clinical trials

During the conduct of clinical trials, two types of errors can occur and they are 'Random Errors' and 'Systematic Errors' , Random errors include measurement errors (such as assay precision,frequency of visits ect) errors due to slopiness (such as transcription errors). Systematic errors include design flaws(such as exclusion of patients with incomplete treatment or unequal schedule of visits); apart from but cannot be classified either to the two errors are Errors resulting from “falsified data” (Fraud) are always serious and must be dealt with accordingly; other errors may be serious or trivial. However, every clinical study must include procedures to avoid or minimize data errors. Most frauds have little impact on the trial results because: they introduce random but not systematic errors (i.e. noise but no bias) in the analyzes they affect secondary variables (e.g. eligibility criteria) their magnitude is too small to have an influence (one site and/or few patients) [2,3]

8 Read more

PRESCRIPTION ERRORS: PREVENTABLE MEDICATION ERRORS

PRESCRIPTION ERRORS: PREVENTABLE MEDICATION ERRORS

Errors of commission are a serious threat to the patients health as compared to the errors of omission which though looks to be harmless but can create a problem for the patient and which occurs 3 to 4 folds more than the errors of commission [17,18,32,33]. Failure to mention the patient’s important information like name, age, M.R number and weight can create problem. If the patient age or weight is not mentioned than it can be problematic while dispensing medicines like cardiac or those related to CNS. The name of physician must be mentioned on the prescription along with his/her signature as in case of any query the pharmacist can easily contact him/her. And above all the prescription should be written clearly which can be read easily as bad handwriting can lead to dispensing of wrong medication. Absences of information related to the drug like dose, route, dosage form, strength and the refill time too should not be taken lightly as they can hinder in dispensing the correct and required dose of medication to the patient. Errors of commission are more severe than the errors of omission as the information is supplied but is incorrect. The wrong dose, strength or frequency may be dangerous for the patient, as the dose more than required can be toxic and below the therapeutic level will have provide effect.

10 Read more

Optimized Basis Sets for the Environment in the Domain-Specific Basis Set Approach of the Incremental Scheme

Optimized Basis Sets for the Environment in the Domain-Specific Basis Set Approach of the Incremental Scheme

In this work DSBSenv minimal basis sets and matching auxiliary basis sets have been de- veloped for H–Ar for use as the environmental basis in the framework of the domain-specific basis set approach of the incremental scheme. These basis sets increase the computational speed performance of the incremental scheme and achieve a comparable accuracy to the pre- vious ad hoc choice of environmental basis. Using the DSBSenv/MP2Fit ABS, the density fitting for the evaluation of the two-electron integrals are three to four orders of magnitude smaller than the BSIE of the DSBSenv OBS. Also the CABS approach to the RI with the DSBSenv/OptRI ABS introduces errors about two to three orders of magnitude smaller than the BSIE.

46 Read more

State space modeling with correlated measurements with application to small area estimation under benchmark constraints

State space modeling with correlated measurements with application to small area estimation under benchmark constraints

Application of the proposed solution to the state-space models employed by the BLS introduces a serious computational problem. The dimension of the state vector in the separate models is of length 30 (see next section), implying that the dimension of the state vector of the joint model fitted to a group of say 12 States would be 360. A possible solution to this problem investigated in the present article is to include the sampling errors as part of the observation (measurement) equation instead of the current practice of modeling their stochastic evolvement over time and including them in the state vector. Implementation of this idea reduces the dimension of each of the separate state vectors by half, because the sampling errors make up 15 ele ments of the state vector.

21 Read more

Machine-learning-assisted correction of correlated qubit errors in a topological code

Machine-learning-assisted correction of correlated qubit errors in a topological code

A quantum computer needs the help of a powerful classical computer to overcome the inherent fragility of entangled qubits. By encoding the quantum in- formation in a nonlocal way, local errors can be de- tected and corrected without destroying the entangle- ment [1, 2]. Since the efficiency of the quantum error correction protocol can make the difference between failure and success of a quantum computation, there is a major push towards more and more efficient de- coders [3]. Topological codes such as the surface code, which store a logical qubit in the topology of an array of physical qubits, are particularly attractive because they combine a favorable performance on small cir- cuits with scalability to larger circuits [4–9].

10 Read more

Auxiliary Basis Sets for Density Fitting in Explicitly Correlated Calculations: The Atoms H–Ar

Auxiliary Basis Sets for Density Fitting in Explicitly Correlated Calculations: The Atoms H–Ar

However, these guidelines have emerged from investigations at the conventional MP2 level and there is no reason to assume that they will be appropriate in the specific context of explicitly correlated methods. As well as the additional two-electron integrals required in the aforementioned computation of the V and B matrices, BSIE is drastically reduced in explicitly correlated methods; meaning that the fitting accuracy must be increased in order that any density fitting errors remain negligible. Recently published MP2Fit sets matched to the cc-pVnZ-PP-F12 basis sets for the post-d main group elements Ga–Rn required functions with an angular momentum of ℓ occ + ℓ OBS + 1 in order to reach sufficient accuracy. This

24 Read more

Show all 8310 documents...