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Bimodal distribution - Wikipedia, the free encyclopedia In statistics, a bimodal distribution is a distribution with two different peaks — that is, there are two distinct values that measurements tend to center around. A good example is the height of a person; the heights of males form a roughly normal distribution, as do those of females, but when added together we obtain a bimodal distribution with values clustering around both the averages. Bimodal distributions are a commonly-used example of how deceptive summary statistics such as the mean, median, and standard deviation can be when used on an arbitrary distribution. en.wikipedia.org /wiki/Bimodal_distribution   (252 words)

Basic Statistics Review - Unit 1 - 112 A symmetric distribution is one in which the shape of left side of the distribution is a "mirror image" of the right side. A positively skewed distribution is one in which the right (positive) tail of the distribution is the long one (see Figure 6.1). A negatively skewed distribution is one in which the left (negative) tail of the distribution is the long one (see Figure 6.2). www.msu.edu /user/sw/statrev/strv112.htm   (362 words)

1.3.3.14.4. Histogram Interpretation: Symmetric and Bimodal The mode of a distribution is that value which is most frequently occurring or has the largest probability of occurrence. For many phenomena, it is quite common for the distribution of the response values to cluster around a single mode (unimodal) and then distribute themselves with lesser frequency out into the tails. A common approach to this case is to fit a mixture of 2 normal or lognormal distributions. www.itl.nist.gov /div898/handbook/eda/section3/histogr4.htm   (262 words)

Evidence for bimodal particle distribution from the spectra of polar mesospheric clouds Evidence for bimodal particle distribution from the spectra of polar mesospheric clouds Dividing the PMC spectra by the solar spectrum yields a scattering spectrum expressible as a matrix-vector formalism of Mie scattering functions and the particle distribution. A lognormal distribution of small particles (mode ∼ 50 nm) produces the overall shape of the spectrum but not the “hump.” Although not unique, a simple bimodal distribution of small particles (r ∼ 50 nm) and large particles (r ∼ 200 nm) describes the scattering spectrum and its hump very well. www.agu.org /pubs/crossref/2004/2004GL020101.shtml   (304 words)

Ch2 Distributions Pt1   (Site not responding. Last check: 2007-10-09) Or to put it in pictorial terms, a negatively skewed distribution is one whose elongated tail extends to the left (the low or "negative") end of the range, while a positively skewed distribution is one whose elongated tail extends to the right (the high or "positive") end of the range. In the mesokurtic distribution illustrated by Section C the clustering is more moderate than in the leptokurtic distribution, and the curve as it falls away from the peak is more tapering than in the platykurtic distribution. In skewed distributions the mean, median, and mode will tend to be separated from one another, with the mean falling toward the tail of the skew, the mode falling away from the tail, at the peak, and the median falling somewhere in-between. vassun.vassar.edu /~lowry/ch2pt1.html   (3381 words)

Repetitive Genetic Inversion of Optical Extinction Data It is apparent that although the larger diameters of the inverted distributions in Fig. Bimodal size distribution models(light curves).obtained by genetic inversion of synthetic data at six wavelengths generated using the heavy fl curve model. This distribution pattern of volcanic aerosol was consistent with the wind fields as well as aerosol optical depths derived from the SeaWifs satellite. www.soest.hawaii.edu /lidar/genetic_inversion_paper.htm   (3450 words)

J6.4 Bimodal distribution of tropical upper tropospheric humidity (2003 - VARIH2O)   (Site not responding. Last check: 2007-10-09) Bimodality in upper-tropospheric water vapor distributions is shown to be a common feature in the tropics, implying sharp gradients between dry and moist regions in space and time. Using this method, the bimodality of water vapor is surveyed in both satellite and in situ observations, as well as a hierarchy of model simulations. Bimodality implies that the homogenization time for moisture, whether physical (mixing) or mathematical (averaging), is long compared to a radiative-subsidence drying time after an injection of moisture by convection. ams.confex.com /ams/annual2003/techprogram/paper_53527.htm   (231 words)

Basic Statistics Review - Unit 1 - 137 This is a bimodal distribution with modes at one referral and eleven referrals. As with the skewed distribution, the bimodal distribution is not uncommon. It is always a good idea to inspect the distribution of the data as part of the process of analysis. www.msu.edu /user/sw/statrev/strv137.htm   (242 words)

CORRELATION LENGTHS OF VERTICAL FLOWPATHS IN MELTING SNOWPACKS The spatial distribution of meltwater flowing from the bottom of melting snowpacks is the result of horizontal and vertical flow paths within the snowpack. The spatial distribution of meltwater flowing from the bottom of melting snowpacks is the result of horizontal and vertical flow paths within the snowpack [Marsh and Woo, 1985; Kattelmann, 1985; Marsh, 1988]. These results suggest that the characteristic distance of 5-7 meters in the bimodal distribution of brightness values may be composed of higher-frequency patterns in vertical flowpaths. snobear.colorado.edu /Markw/Flowpaths/flowpaths.html   (4081 words)

Descriptive Statistics: Distributions of Variables The distribution of a variable refers to the way the scores are distributed across all possible values or levels of the variable. A frequency distribution can be said to have a shape, which is easy to see when it is displayed as a histogram. A symmetrical frequency distribution has a left side that is roughly a mirror image of its right side, whereas a skewed (asymmetrical) distribution is clearly “lopsided.”  A positively skewed distribution has more low scores and fewer high scores. psych.csufresno.edu /price/psych144/desc.html   (683 words)

Bimodal Distribution of Angiographic Measures of Restenosis Six Months After Coronary Stent Placement -- Schömig ...   (Site not responding. Last check: 2007-10-09) a normal distribution of the response of the vessel to the intervention. Bimodal distribution of diameter stenosis 4 to 12 months after angioplasty: implications for definitions and interpretation of restenosis. Contributions of frequency distribution analysis to the understanding of coronary restenosis: a reappraisal of the gaussian curve. circ.ahajournals.org /cgi/content/full/96/11/3880   (4531 words)

Hydraulic cement composition - Patent 4353746 The preference for fractions having narrow bands of size in a bimodal distribution is likewise preferred in the case of a trimodal distribution. The multi-modal distribution of particulate hydraulic cement may be achieved by modifying the comminution of the raw cement particles and using appropriate classifying, separating or mixing procedures. Preferably, the particle size distribution of the hydraulic cement is chosen so as to enable a suitably deformable cement composition containing a water proportion in the range 8% to 15% by weight of the cement to be produced. www.freepatentsonline.com /4353746.html   (3614 words)

Creating Bimodal Distributions To model these two situations, you need a "bimodal" distribution, where one hump represents revenue with no competition and another hump represents the reduced revenue that results from competition. Although the Crystal Ball distribution gallery contains only single-mode distributions, it is possible to create a bimodal distribution through an IF statement in Excel. "I use this technique to help create a risked distribution where the one distribution is the failure case (an exploration dry hole or the dry hole cost), and the second is the successful exploration case distribution of values or reserves. www.decisioneering.com /support/cbtips/cb_tips71.html   (463 words)

Normal Distribution and z-values   (Site not responding. Last check: 2007-10-09) Note that though the underlying distribution is bimodal, the distribution of the forty means is "heaped" and close to symmetrical. Understanding the SHAPE of the distribution of many sample means is a key to using a single sample mean (a statistic) to estimate the population mean (a parameter). The standard deviation of the distribution of the sample means is equal to the actual population standard deviation divided by the square root of n. www.comfsm.fm /~dleeling/statistics/notes07.html   (859 words)

Evolution - Wikipedia, the free encyclopedia On his return, he was informed in 1837 by Richard Owen that fragments of armor were from the gigantic extinct glyptodons, creatures related to the modern armadillos he had seen living nearby. The similarities between these two unusually scaly mammals and their geographic distribution provided Darwin with a clue that helped him develop his theory of how evolution occurs. For instance, monotremes, such as platypus, and most marsupials, like kangaroos or koalas, are found only in Australia showing that their common ancestor with placental mammals lived before the submerging of the ancient land bridge between Australia and Asia. en.wikipedia.org /wiki/Evolution   (9682 words)

Particle Size Distributions Shown in Figure 1 is the bimodal size distribution of ice crystals often seen in cloud observations [e.g., Mitchell et al., 1996; Platt, 1997]. The bimodal distribution of ice particle spectra is not fully understood although it has been speculated as a result of balancing between the nucleation of ice particles and the removal of ice particles by aggregation and enhanced diffusion growth via ventilation [Mitchell, 1994]. Bimodal size distributions are used to fit the lidar/radar data, showing a much wider spread of the large particle mode than the above two parameterizations. mls.jpl.nasa.gov /dwu/cloud/RetrievalUncertainties.html   (1234 words)

[No title] "At what point does a bimodal distribution become just a distribution with two peaks?" Except for a few quite extreme situations, dealing with mixtures of distributions and the like, it will rarely ever be the case that the two peaks of a distribution are EXACTLY the same height. Date: Thursday, August 30, 2001 2:19 PM A bimodal distribution is often thought to be a mixture of two other distributions with different modes. In the bimodal case, some refer to the higher "hump" as the major mode and the other as the minor mode. core.ecu.edu /psyc/wuenschk/docs30/Shapes.doc   (503 words)

Audience Response Graphs, About - Understanding and Interpreting Bimodal Distribution The bimodal graph is characterized by two distinct peaks. A bimodal distribution typically indicates that there is substantial disagreement. Although the bimodal response may require some effort to clarify, a rectangular distribution is the often the most difficult. www.audience-response-rentals.com /interpretation/bimodal.htm   (230 words)

STAT-LAM Temperature Both display a bimodal distribution with the cool weak bias in the simulation evident in the small shift toward cooler temperatures. Maximum temperature also has a bimodal distribution in both the observations and the simulation, though it is more clearly evident in the simulation results. The bimodal distribution could be obscured in the observations by removal on just one or two categories, i.e., it is not as robust. www.pircs.iastate.edu /people/Gutowski/STAT_LAM/SLtmm.html   (290 words)

Niche Modeling » How are bimodal distributions created and modeled? Humans are probably bimodal in feature space (men and women being distinct enough to classify as one or the other with a high degree of accuracy) - the relevant state in this case being sex or its genetic proxy. In my mind, a bimodal distribution would likely be modeled by a mixture of distributions chosen to reflect the observed data (or nonparametrically estimated by a kernal estimate, perhaps). Based on your reference to the distribution of species, it seems that you might be interested in a test that works for two dimensions (or more, if the species is aquatic, I guess). landshape.org /enm/how-are-bimodal-distributions-created-and-modeled   (991 words)

National MS Society | Clinical Study Measures   (Site not responding. Last check: 2007-10-09) When large numbers of patients are tested with a given instrument, the scores are often plotted on a graph in which the horizontal axis represents the scores (from low to high) and the vertical axis represents the number of patients obtaining a given score. This graph may take the form of a "bell-shaped" curve in which the distribution of scores forms a single, rounded peak in the middle of the graph and then gently tapers toward either extreme of the scale, i.e., like a bell. A bimodal distribution may result from an undesirable characteristic of a scale in which different scores along the scale do not represent equal intervals. www.nationalmssociety.org /MUCS_glossary1.asp   (1284 words)

Measures of Central Tendancy - Faculty of Arts at The University of Auckland, New Zealand Distribution A represents Ann-Geselle's frequency of 'ouis' in her everyday conversation, and distribution B represents her frequency of 'yes's' in her everyday conversation. In computing the median from a frequency distribution based on the score of 30 pupils, Judith noted that the median is located in the class interval whose score limite are 60-64. He decides that he is interested in the bulk of the scores and does not want the very few deviant scores to alter extensively his measure of central tendency. www.arts.auckland.ac.nz /staff/index.cfm?P=4875   (1365 words)

ASTRONOMY: ON GLOBULAR CLUSTERS We know that the color of old stellar systems correlates with their metallicity [2], so the bimodal colors were interpreted as a bimodal metallicity distribution, and therefore as evidence for the predicted two populations of clusters. New work[3] shows that a single cluster population with a broad monomodal metallicity distribution can have a bimodal distribution of color, because the relation between color and metallicity is not linear. From the time of its discovery, the bimodal color distribution of the clusters in elliptical galaxies was interpreted as a bimodal metallicity distribution. scienceweek.com /2006/sw060324-1.htm   (1777 words)

Math Forum - Ask Dr. Math   (Site not responding. Last check: 2007-10-09) I know that if a distribution is sharp and peaked, then the standard deviation is small. We call the smaller of the peaks a "local mode." If the two peaks are the same height we say that the distribution is "bimodal" or "multimodal." But you have to be careful that you're not over-scrutinizing the data. A small increase in a generally decreasing pattern may just be a glitch, an aberration of how the data were sampled, and may not be significant. mathforum.org /library/drmath/view/52795.html   (227 words)

Stats: Searching for bimodality (August 4, 2004) The first step is to see if the distribution of values for some measurement has a bimodal distribution. A second mode is an indication of a subgroup of patients that may have a genetic variation from the rest of the patients. If you had nine data values, the smallest one would be compared to the 10th percentile, the next smallest one to the 20th percentile and so forth, until the largest one was compared to the 90th percentile of a normal distribution. www.childrens-mercy.org /stats/weblog2004/bimodality.asp   (509 words)

Dispersion Technology, Inc.- Instruments for Characterizing Concentrated Colloidal Dispersions. Particle size distribution of zirconia is wider than that of the alumina AA-2 as it is shown on Figure 13 for individual systems. Acoustic spectroscopy is capable to characterize particle size distribution of individual materials as well as of their mixtures. These computed size distributions are consistent with general understanding of the physical chemistry of such a cement system. www.dispersion.com /pages/applications/applications.htm   (3253 words)

Rotation Periods of PMS Stars   (Site not responding. Last check: 2007-10-09) The main feature of the figure is the bimodal distribution of the periods. The distribution is clearly bimodal; there are 20 stars in the ``gap'' from 4 to 6 days which is about half the number expected for a smooth distribution. The gap may arise either because the distribution has a hole, or because it is made up of two distinct distributions. hea-www.harvard.edu /~swolk/thesis/intro/node5.html   (712 words)

Astronomy & Astrophysics Bimodal distribution of the autocorrelation function in gamma-ray bursts Autocorrelation functions (ACFs) are studied for a sample of 16 long gamma-ray bursts (GRBs) with known redshift z, that were observed by the BATSE and Konus experiments. When corrected for cosmic time dilation, the ACF shows a bimodal distribution. www.edpsciences.org /articles/aa/abs/2004/17/aa0567/aa0567.html   (198 words)

Determination of Molecular Weight The distribution shown above is bimodal (two identifiable peaks) and skewed (neither of the peaks is a symmetric about their means and the entire bimodal distribution is not symmetric about the mean. For a simple unimodal symmetric distribution only the first and second moments are needed to describe the distribution if a functional form such as a Gaussian or Lorentzian distribution is appropriate. In general, the number of distinct moments needed to fully describe a distribution is equal to the number of features in the distribution curve. www.eng.uc.edu /~gbeaucag/Classes/Characterization/MolecularWeighthtml/MolecularWeight.html   (2323 words)

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