Colour patch size and measurement error using reflectance spectrophotometry

Experiments were conducted to test the accuracy of a global positioning system (GPS) in measuring the area of simulated weed patches of varying size and to determine the accuracy in navigating back to particular points in a field. Circular areas of 5, 50, and 500 m2 were established and measured using point and polygon features of a GPS. The GPS estimations of the area of those patches had errors ranging from 7 to 45%, 6 to 15%, and 3 to 6%, respectively, when compared to actual measurements. As patch size increased, errors decreased. A curve describing the relationship between GPS error and patch size had an excellent fit (r2 = 0.92). The error remained the same in all measurements across all patch sizes, but composed a smaller percentage of large patches. The GPS had submeter accuracy in navigation to the correct quadrat 73% of the time, located the correct quadrat 27% of the time, and invariably navigated to within 1.58 m of the correct quadrat. The relationship between patch size and measurement error was applied to natural infestations of hemp dogbane.

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NO EVIDENCE OF FEMALE CHOICE FOR A CONDITION-DEPENDENT TRAIT IN THE AGAMID LIZARD, CTENOPHORUS ORNATUS

Behaviour ◽

10.1163/156853901753286515 ◽

2001 ◽

Vol 138 (8) ◽

pp. 965-980 ◽

Cited By ~ 38

Author(s):

N. Justin Marshall ◽

Natasha Lebas

Keyword(s):

Female Choice ◽

Patch Size ◽

Spatial Association ◽

Female Mate Choice ◽

Condition Dependence ◽

Reflectance Spectrophotometry ◽

Lizard Species ◽

Agamid Lizard ◽

Post Hoc ◽

Accurate Quantification

AbstractFemale choice has rarely been documented in reptiles. In this study we examined the variation, condition-dependence and female preference for a range of male morphological and colour traits in the agamid lizard, Ctenophorus ornatus. Colour traits were measured with reflectance spectrophotometry which allows the accurate quantification of colour traits independent of the human visual system. All the colour traits varied greatly in brightness but only the throat showed high variation in the spectral shape. For the morphological traits, chest patch size showed the highest amount of variation and was also condition-dependent. Males with a larger chest patch also had a patch which was a darker black. Female mate choice trials were conducted on male chest patch size and body size, which is the trait females have preferred in other lizard species. Females showed no preference, measured as spatial association, for larger males or males with bigger chest patches. In post-hoc tests females did not prefer males with brighter throats or darker chests. Our findings suggest that females show no spatial discrimination between males on the basis of a range of traits most expected to influence female choice.

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Benefits from Computerized Adaptive Testing as Seen in Simulation Studies

European Journal of Psychological Assessment ◽

10.1027//1015-5759.15.2.91 ◽

1999 ◽

Vol 15 (2) ◽

pp. 91-98 ◽

Cited By ~ 10

Author(s):

Lutz F. Hornke

Keyword(s):

Measurement Error ◽

Computerized Adaptive Testing ◽

Test Procedure ◽

Adaptive Testing ◽

Parameter Estimates ◽

Simulation Studies ◽

Computerized Adaptive Test ◽

Item Banks ◽

Item Parameters ◽

General Reliability

Summary: Item parameters for several hundreds of items were estimated based on empirical data from several thousands of subjects. The logistic one-parameter (1PL) and two-parameter (2PL) model estimates were evaluated. However, model fit showed that only a subset of items complied sufficiently, so that the remaining ones were assembled in well-fitting item banks. In several simulation studies 5000 simulated responses were generated in accordance with a computerized adaptive test procedure along with person parameters. A general reliability of .80 or a standard error of measurement of .44 was used as a stopping rule to end CAT testing. We also recorded how often each item was used by all simulees. Person-parameter estimates based on CAT correlated higher than .90 with true values simulated. For all 1PL fitting item banks most simulees used more than 20 items but less than 30 items to reach the pre-set level of measurement error. However, testing based on item banks that complied to the 2PL revealed that, on average, only 10 items were sufficient to end testing at the same measurement error level. Both clearly demonstrate the precision and economy of computerized adaptive testing. Empirical evaluations from everyday uses will show whether these trends will hold up in practice. If so, CAT will become possible and reasonable with some 150 well-calibrated 2PL items.

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