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Topic: Observational error

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	OBSERVATIONAL ERROR
		This term ought to mean an error of observation but sometimes occurs as meaning a response error.
		Observational error is the difference between a measured value of quantity and its true value.
		The random error (or random variation) is due to factors which we cannot (or do not) control.
	www.websters-online-dictionary.org /definition/english/ob/observational+error.html (387 words)

	Observational error - Wikipedia, the free encyclopedia
		Observational error is the difference between a measured value of quantity and its true value.
		When either randomness or uncertainty modeled by probability theory is attributed to such errors, they are "errors" in the sense in which that term is used in statistics; see errors and residuals in statistics.
		The random error (or random variation) is due to factors which we cannot (or do not) control.
	en.wikipedia.org /?title=Observational_error (245 words)

	Quirks.com - Articles - Increasing survey accuracy
		Sampling error-This error occurs when we survey only a sample of the population rather than every person, i.e., we may survey 1,000 households rather than the approximate 93 million households comprising the total U.S. population.
		Observational error-This type of error includes incorrect measurements caused by a variety of factors such as the respondent's failure to recall information accurately (e.g., the last brand bought).
		One way to decrease observational error is by enhancing the communication between interviewer and respondent, thereby improving the collection of accurate data.
	www.quirks.com /articles/a1992/19920606.aspx?searchID=2188819&sort=9 (1286 words)

	Error (Site not responding. Last check: 2007-11-04)
		Statistical error is caused by random (and therefore inherently unpredictable) fluctuations in the measurement apparatus, whereas systematic error is caused by an unknown but nonrandom fluctuation.
		Errors in a system can also be latent design errors that may go unnoticed for years, until the right set of circumstances arises that cause them to become active.
		An error is judged by the official scorer when a runner advances a base because of a fielding mistake, and perfect play would have prevented the advancement, and the mistake was physical.
	www.worldhistory.com /wiki/E/Error.htm (622 words)

	page15 (Site not responding. Last check: 2007-11-04)
		The observation error distributions are generally not Gaussian, which violates a common assumption in the assimilation theory.
		Observational error distributions can also be non-Gaussian due to gross errors in the data created by transmission errors and other sources.
		Moreover, it is much easier to quantify errors when the observation is the raw signal from the instrument rather than a construct of the raw signal, questionable approximations, and supplemental information, sometimes even a prediction model.
	www.mmm.ucar.edu /uswrp/reports/five_year_plan/page15.html (421 words)

	Model error in weather forecasting: does chaos matter (Site not responding. Last check: 2007-11-04)
		Errors are expressed as a weighted sum of the wind and temperature errors between the forecast and the analysis (the analysis being our best approximation to the real weather), integrated vertically over all model levels, and horizontally over the Northern hemisphere.
		The negative curvature of the model error is due to the fact that, in high dimension spaces, vectors tend to be orthogonal to one another.
		Also, because initial condition error and model error are unrelated to one another (the first is a property of the model alone, the second depends on the real weather), the singular vectors are expected to be orthogonal to the model error.
	www.beatrizl.freeserve.co.uk /AGUposter.htm (2220 words)

	NationMaster - Encyclopedia: Planning statistical research
		In every type of research, we must be concerned with managing the observational error that is inherent in all empirical research.
		We can increase the precision of our research by Observational error is the difference between a measured value of quantity and its true value.
		Physiology is an example of a discipline in which this kind of focus is common.
	www.nationmaster.com /encyclopedia/Planning-statistical-research (622 words)

	Observational Errors and Limitations
		These errors could be due to inaccurate leveling of the instrument, motion of the instrument caused by traffic, microseisms, or people walking about, or errors in reading the output of the instrument.
		If the errors associated with the readings are random, it can be shown that the reading error is reduced by the square root of the number of observations made.
		Download the observation error data set to your machine The first column in the data set lists the time of day in hours and minutes (Hr:mn) that each observation was made, and the second column is the relative gravity reading in mGals.
	www.earthsci.unimelb.edu.au /ES304/MODULES/GRAV/OBSERVATIONS/obs.html (1444 words)

	[No title]
		THFG documented the scale-dependence of the representativeness error, finding that its magnitude was dependent on the difference in variability between the grid scale and the scale of the radar data (2 km).
		Since representativeness error increased with the scale of averaging for the observation-point approach (referred to as area-to-point conversion; A-P), it was interpreted that error in assigning areal averages to observation points increases as the block area becomes larger.
		This is because the representativeness error is observed to decrease as the difference in variability between the model output and the observations is reduced.
	www.atmos.washington.edu /~epgrimit/misc/WAF_NOTE_0.5.DOC (1599 words)

	PREPBUFR PROCESSING AT NCEP
		The background guess information is used by certain quality control programs while the observation error is used by the analysis to weigh the observations.
		The forecast background (first guess) interpolated to each observation location is also encoded in the PREPBUFR file in all networks and the observational error, read in from a look-up table, is also encoded in the PREPBUFR file in the AVN and FNL networks.
		Each observation is subjected to the optimum interpolation formalism using all observations except itself in each check.
	www.emc.ncep.noaa.gov /mmb/data_processing/prepbufr.doc/document.htm (3783 words)

	Features
		Many people refer to the inexactness of experiments as "experimental error." This is what I mean by the word noise, except I think that noise describes the issue better because some of the inexactness of experiments is unavoidable, and therefore unlike an error of some type.
		The observational unit doesn't have to be identical to the experimental unit.
		Observational error or noise is a part of the total noise in an experiment but it cannot tell us anything about the experimental noise.
	www.sas.org /E-Bulletin/2001-12-21/features/features.html (1130 words)

	Towards Estimating Climatic Trends in SST, Part 2: Random Errors (Site not responding. Last check: 2007-11-04)
		A statistical technique, semivariogram analysis, is used to isolate the variance due to the observational error from that due to the spatial variability in a dataset of the differences of paired SST reports.
		The error estimates are robust to changes in the details of the regression method used to estimate the spatial variability.
		The resulting error estimates are shown to vary with region, time, the quality control applied, the method of measurement, the recruiting country and the source of the data.
	www.soc.soton.ac.uk /JRD/MET/ABSTRACTS/sst_part2.html (267 words)

	[No title]
		The main idea in all three methods is to estimate the amount of initial error in the observations and attempt to come up with a range of possibilities that are all equally valid due to the observational uncertainty.
		Suppose the error is represented by E, and the perturbation is represented by P. If two runs of the model are taken, with E+P and E-P, one run has to be closer to the correct value as long as P is not bigger than 2E.
		Their data showed that observational errors will not have a great effect on your forecast when high certainty is reached, because ensemble members are all close to agreement on the future state of the atmosphere.
	incolor.inetnebr.com /string/ensemble/paper.html (2050 words)

	The LDAD Observation QC and Monitoring System
		The error threshold (to which the absolute value of the difference between analyzed and observed values is compared) is a function of the forecast error, the observational measurement error, and the expected analysis error (Belousov et al.
		Including the OI error in the threshold is necessary to determine whether large differences between analyses and observations are caused by observational error or uncertainty in the analyzed value at the observation point.
		The expected observational error accounts for both the measurement and the sampling (unrepresentativeness) errors present in the observations.
	www-sdd.fsl.noaa.gov /~fxa/publications/10th_SMOI_98/Miller-et-al.SMOI98.html (3949 words)

	Environmental Health Perspectives: Exposure Measurement Error in Time-Series Studies of Air Pollution: Concepts and ...
		Because measurement error may have substantial implications for interpreting epidemiologic studies on air pollution, particularly the time-series analyses, we developed a systematic conceptual formulation of the problem of measurement error in epidemiologic studies of air pollution and then considered the consequences within this formulation.
		In general, exposure measurement error tends to blunt the sensitivity of epidemiologic studies for detecting the effects of environmental agents, although the specific impact of exposure error on effect estimates depends on several factors including the study design, the types of error, and the relationships between the outcome and the independent variables (1,2).
		Because exposure measurement error may have substantial implications for interpreting epidemiologic studies on air pollution, particularly the time-series analyses, we developed one systematic conceptual formulation of the problem of exposure error in epidemiologic time-series studies of air pollution and considered the possible consequences for relative risk estimation.
	www.findarticles.com /p/articles/mi_m0CYP/is_5_108/ai_63322040 (1382 words)

	GLOBAL OCEAN ASSIMILATION SYSTEM
		The model and observational error covariances are assumed to have a Gaussian horizontal structure with latitudinal and longitudinal scales specified.
		The observational errors are assumed to be spatially uncorrelated, with a higher error variance in mid and high latitude western boundary regions to account for sampling biases due to mesoscale variability which is not resolvable by this relatively coarse ocean model.
		Since the model errors are assumed to be vertically uncorrelated, the variational scheme is solved independently on horizontal model levels using a conjugate gradient solver.
	www.gfdl.noaa.gov /~mh2/assimilation.html (758 words)

	Measurement Errors
		Systematic errors mean that different methods of measurement are being applied to the same variable.
		This is due to random errors associated with grading the questions and assigning a point value in a lightly subjective manner.
		Understanding the role of measurement errors is crucial to proper data interpretation.
	zebu.uoregon.edu /1999/es202/l16.html (765 words)

	Observational error -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-11-04)
		The (Click link for more info and facts about systematic error) systematic error is sometimes called (Click link for more info and facts about statistical bias) statistical bias.
		Part of the education in every (A particular branch of scientific knowledge) science is how to use the standard instruments of the discipline.
		The (Click link for more info and facts about random error) random error (or (Click link for more info and facts about random variation) random variation) is due to factors which we cannot (or do not) control.
	www.absoluteastronomy.com /encyclopedia/o/ob/observational_error.htm (336 words)

	NPG - Abstract
		However, a prescribed observational error distribution may project on states that are off the attractor, resulting in unrepresentative error growth.
		The 'correct' error growth problem examines growth for the projection of the observational error distribution onto the model's attractor.
		While the magnitude of these errors is not large in the simple dynamical systems examined, the impact could be much larger in more realistic forecast models.
	www.copernicus.org /EGU/npg/4/157.htm (284 words)

	Statistical dispersion - Wikipedia, the free encyclopedia
		One of the forms in which statistical variability is realized in the empirical sciences is that of differences in repeated measurements of the same quantity.
		In the physical sciences, such variability may result only from random measurement errors: instrument measurements are often not perfectly precise and accurate.
		One may assume that the quantity being measured is unchanging and stable, and that the variation between measurements is due to observational error.
	www.wikipedia.com /wiki/Statistical_variability (321 words)

	Observational research techniques
		Direct observation, if carried out in a structured and disciplined way is one of the purest forms on research, as it taps directly into behaviour, rather than perceptions, secondary or self-reports of behaviour.
		Objective observation, expecially from observers that have had an opportunity to compare cases using an objective structured method (eg: observations in several fast food chain oulets, observation of several flight sectors for an airline company, observations of several different airlines), provides a far more realistic data set.
		Though generally more expensive, observational techniques are often of higher value than the cheaper self report methods, simply because they focus on actual behaviour.
	www.orientpacific.com /observational-techniques.htm (640 words)

	Intelligent Enterprise Magazine - Data in the Time of Cholera
		The one thing I have not seen in data warehousing, which plays a key role in the other observational sciences, is the concept of observational error and error propagation.
		Observational scientists have figured out ways to deal with observational errors by eliminating systematic recording errors, reducing random errors in the recording process, and increasing the signal-to-noise ratio of data in the data analysis step through various mathematical techniques.
		This missing piece of observational data allowed the geologists and geophysicists to realize that mountains resulted when giant plates on the surface of the earth collided like a very bad car accident in slow motion.
	www.intelligententerprise.com /010308/feat3_3.jhtml (737 words)

	HD 209458 (Site not responding. Last check: 2007-11-04)
		As we are interested in the ratio of DN counts, we must combine the error in each image in fractional quadrature to determine the error in each ratio value.
		This inherent error is then added in quadrature to the propagated error expected from our equipment and analysis, which is dominated by the uncertainty in the flat field.
		Taking a larger number of observations and increasing the exposure duration are two ways to reduce error, ideally putting observed error in the regime of theoretical error.
	www.ugastro.berkeley.edu /~alicia/error.html (274 words)

	Observational error - Weather Terms and Definitions by Health Dictionary
		Systematic errors affect the whole of a series of observations in nearly the same way.
		The personal equation of an observer may lead him or her to make small systematic errors in his or her readings, for example, if the scale is not at eye level.
		Random errors, which appear in any series of observations, are generally small and as likely to be positive as negative.
	www.sciencedictionary.org /weather-term-details/Observational-error (170 words)

	Environmental Health Perspectives: Exposure Measurement Error in Time-Series Studi... @ HighBeam Research (Site not responding. Last check: 2007-11-04)
		In contrast, under the classical error model [[Beta].sub.z] obtained by regressing [y.sub.t] on the imperfect measure exposure [z.sub.t] is a biased estimate of [[Beta].sub.x] In the simple linear regression with one explanatory variable, [[Beta].sub.z] is expected to be smaller than [[Beta].sub.x], or attenuated.
		In the Berkson error case, the assumption that [x.sub.t] is an imprecise version of [z.sub.t] or E([x.sub.t][z.sub.t]) = [z.sub.t] still assures that the estimates of the regression coefficients are unbiased, as in the univariate instance.
		In certain specific time-series models, the degree of attentuation due to classical error might be reduced became to account for the autocorrelated errors, the ARIMA filters or smooths both the responses and the predictors that might reduce the degree of measurement error.
	highbeam.com /library/doc0.asp?DOCID=1G1:63322040&... (8500 words)

	AMIP-CMIP Comparison (Site not responding. Last check: 2007-11-04)
		Errors in wind and temperature are connected by the principle of geostrophic balance.
		Space-time pattern errors could arise in a simulated field that is perfectly correlated with observed patterns but contains erroneous variance magnitudes, or vice versa.
		We are grateful to the CSM and PCM modelers for contributing their results and to Michael Fiorino and Benjamin D. Santer for useful discussions.
	www.lmd.jussieu.fr /pcmdi-mirror/cmip/Comparison_MS/covey_text.html (5242 words)

	Energy Citations Database (ECD) - Energy and Energy-Related Bibliographic Citations
		When the velocity field is retrieved by a variational data assimilation method from the tracer (reflectivity) pattern movement observed by a Doppler radar, the accuracy of the retrieved velocity is affected by the observational error and data resolution.
		This systematic error is caused by the nonlinear response of the retrieved velocity to the observed data.
		In addition, there is also a nonsystematic error in the retrieved velocity caused by the observational errors in the tracer field and tracer gradient field.
	www.osti.gov /energycitations/product.biblio.jsp?osti_id=443500 (284 words)

	Return to ‘Inner Sense’:
		It is quite natural to think of introspection as a kind of “inner sense, by means of which the mind intuits itself or its inner state,” as Kant said; or as a kind of “perception of what passes in a man’s own mind,” as Locke said.
		Inner sense models of introspection, on the other hand, allow for the possibility of brute error by maintaining that in properly functioning rational agents there is merely a contingent causal relation between introspective judgments and the thought contents they attribute.
		I say ‘apparent’ epistemological disadvantage because I argue elsewhere that even if introspective judgments are immune to brute error, there remains an important qualitative difference between introspective and ordinary perceptual judgments—one that is sufficient to ground the distinctive epistemic privilege enjoyed by introspective judgments over ordinary perceptual judgments.
	www.siue.edu /~wlarkin/research/concepts.html (6320 words)

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