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• 31. [Article] A critical examination of the ageing method for sablefish (Anoplopoma fimbria) from the U.S. west coast using edge analysis and oxytetracycline

  This thesis evaluates the current break-and-burn ageing method for the southern stock (U.S. west coast) of sablefish (Anoplopoma fimbria). Differences in growth rates between the northern (north of Vancouver ...

  Citation × Citation Citation Abstract Copy Title: A critical examination of the ageing method for sablefish (Anoplopoma fimbria) from the U.S. west coast using edge analysis and oxytetracycline Author: O'Malley, Joseph M. This thesis evaluates the current break-and-burn ageing method for the southern stock (U.S. west coast) of sablefish (Anoplopoma fimbria). Differences in growth rates between the northern (north of Vancouver Island, BC) and southern stocks (south of Vancouver Island, BC) and results from a radiometric study conducted on fish from the southern stock suggest that the ageing method, developed from fish from the northern stock, may not be appropriate for fish in the southern stock. An edge analysis, using fish landed in Oregon, confirmed the formation of one hyaline zone annually. The timing of the deposition of the hyaline zone, May through September, is unique for fish from temperate waters. Sablefish tagged and injected with oxytetracycline (OTC) did not indicate ageing error significant enough to warrant the development of a new ageing method but some amendments to the current ageing method are recommended: do not excessively split marks in the transition zone (the area on the otolith that corresponds to the change from early fast growth to older slow growth); if multiple marks originate from the same spot on the ventral edge of the otolith, concentrate on the narrowing opaque zones when determining which marks to count as annuli; and assign age ranges or discard otoliths that display odd growth patterns. These amendments may increase the accuracy and precision of sablefish age estimates. Neither final age nor any of the auxiliary catch data (sex, size, depth, and latitude at recapture) contributed significantly to the ageing error. It is also recommended that the thin section method of preparing otoliths be used in future sablefish OTC studies. Title: A critical examination of the ageing method for sablefish (Anoplopoma fimbria) from the U.S. west coast using edge analysis and oxytetracycline Author: O'Malley, Joseph M. This thesis evaluates the current break-and-burn ageing method for the southern stock (U.S. west coast) of sablefish (Anoplopoma fimbria). Differences in growth rates between the northern (north of Vancouver Island, BC) and southern stocks (south of Vancouver Island, BC) and results from a radiometric study conducted on fish from the southern stock suggest that the ageing method, developed from fish from the northern stock, may not be appropriate for fish in the southern stock. An edge analysis, using fish landed in Oregon, confirmed the formation of one hyaline zone annually. The timing of the deposition of the hyaline zone, May through September, is unique for fish from temperate waters. Sablefish tagged and injected with oxytetracycline (OTC) did not indicate ageing error significant enough to warrant the development of a new ageing method but some amendments to the current ageing method are recommended: do not excessively split marks in the transition zone (the area on the otolith that corresponds to the change from early fast growth to older slow growth); if multiple marks originate from the same spot on the ventral edge of the otolith, concentrate on the narrowing opaque zones when determining which marks to count as annuli; and assign age ranges or discard otoliths that display odd growth patterns. These amendments may increase the accuracy and precision of sablefish age estimates. Neither final age nor any of the auxiliary catch data (sex, size, depth, and latitude at recapture) contributed significantly to the ageing error. It is also recommended that the thin section method of preparing otoliths be used in future sablefish OTC studies. Close

• 32. [Article] Relations between Preschool Attention Span-Persistence and Age 25 Educational Outcomes

  Acknowledgements: We are very grateful to Robin Corley for assistance with data management.

  Citation × Citation Citation Abstract Copy Title: Relations between Preschool Attention Span-Persistence and Age 25 Educational Outcomes Author: Stallings, Michael C., McClelland, Megan M., Piccinin, Andrea, Rhea, Sally Ann, Acock, Alan C. Acknowledgements: We are very grateful to Robin Corley for assistance with data management. Title: Relations between Preschool Attention Span-Persistence and Age 25 Educational Outcomes Author: Stallings, Michael C., McClelland, Megan M., Piccinin, Andrea, Rhea, Sally Ann, Acock, Alan C. Acknowledgements: We are very grateful to Robin Corley for assistance with data management. Close

• 33. [Article] Some socio-economic factors associated with clothing purchasing habits of a selected group of women 60 years of age and over

  The purpose of this study was to identity clothing purchasing habits of women 60 years of age and over. Data for this study were obtained from a questionnaire administered to 94 women, 60 years of age ...

  Citation × Citation Citation Abstract Copy Title: Some socio-economic factors associated with clothing purchasing habits of a selected group of women 60 years of age and over Author: Burnett, Marialyce The purpose of this study was to identity clothing purchasing habits of women 60 years of age and over. Data for this study were obtained from a questionnaire administered to 94 women, 60 years of age and over, living in Portland, Corvallis, and Eugene, Oregon. The sample was analyzed on the basis of two age groups (60 to 69 and 70 and over), three income groups (less than $999, $1000 to $1999, and $2000 and over), and three education groups (less than high school, high school, and more than high school). The chi square test was used to determine if there were relationships between clothing purchasing habits and the factors of age, income, and education of this age group. Age, income, and education were related to certain aspects of the purchasing habits of women 60 years of age and over. There was a significant relationship between the factors of age and income and whether the women enjoyed shopping for dresses. Age and education had significant relationships when analyzed with the frequency of looking at magazines, catalogues, newspapers, pattern books, or displays. There was a significant relationship between income and education and the frequency of buying a dress after first seeing it pictured in a a catalogue, a newspaper, or a window display. Age and income were important factors in whether the women wished stores carried a wider selection from which to choose. Older women have an interest in clothing. Comfort and fit were found to be the most important factors to consider in the selection of a dress. The majority of the women shopped for dresses in department stores which were located in their home towns. Most of the women shopped by themselves and preferred to do so. The majority of the women wanted their dresses to be of the current fashion trends, and many of the women were able to find styles that they liked to wear. Title: Some socio-economic factors associated with clothing purchasing habits of a selected group of women 60 years of age and over Author: Burnett, Marialyce The purpose of this study was to identity clothing purchasing habits of women 60 years of age and over. Data for this study were obtained from a questionnaire administered to 94 women, 60 years of age and over, living in Portland, Corvallis, and Eugene, Oregon. The sample was analyzed on the basis of two age groups (60 to 69 and 70 and over), three income groups (less than $999, $1000 to $1999, and $2000 and over), and three education groups (less than high school, high school, and more than high school). The chi square test was used to determine if there were relationships between clothing purchasing habits and the factors of age, income, and education of this age group. Age, income, and education were related to certain aspects of the purchasing habits of women 60 years of age and over. There was a significant relationship between the factors of age and income and whether the women enjoyed shopping for dresses. Age and education had significant relationships when analyzed with the frequency of looking at magazines, catalogues, newspapers, pattern books, or displays. There was a significant relationship between income and education and the frequency of buying a dress after first seeing it pictured in a a catalogue, a newspaper, or a window display. Age and income were important factors in whether the women wished stores carried a wider selection from which to choose. Older women have an interest in clothing. Comfort and fit were found to be the most important factors to consider in the selection of a dress. The majority of the women shopped for dresses in department stores which were located in their home towns. Most of the women shopped by themselves and preferred to do so. The majority of the women wanted their dresses to be of the current fashion trends, and many of the women were able to find styles that they liked to wear. Close

• 34. [Article] Are There Gender Differences in Stress Response in Older Adults? Findings from the Normative Aging Study

  In this study, we explored the relationships among gender, age, daily stressors, positive and negative affect, and neuroticism on cortisol outcomes in older men and women. We were particularly interested ...

  Citation × Citation Citation Abstract Copy Title: Are There Gender Differences in Stress Response in Older Adults? Findings from the Normative Aging Study Author: Proulx, Jeffrey A. In this study, we explored the relationships among gender, age, daily stressors, positive and negative affect, and neuroticism on cortisol outcomes in older men and women. We were particularly interested in whether variation in positive affect would have an effect on variation in negative affect and if this relationship would mediate the stress process. Further, we were interested in whether women would have lower cortisol outcomes as a result of this process. The participants in this study included 96 men (mean age = 79) and 65 of their wives (mean age = 75) who took part in an at-home 8- day daily diary study as part of the Normative Aging Study (NAS). This study uses data collected on four of those days in which participants provided 4 measures of salivary cortisol that we matched with a NAS version of the Daily Inventory of Stressful Events (DISE; Almeida, Wethington, & Kessler, 2002), PANAS (Watson, Clark, & Tellegen, 1988), and a 2007 assessment of neuroticism (Goldberg, 1992). Bivariate, regression, and three-level MLM-mediated-moderated analyses indicated that age had a significant effect on negative affect reports, but only for women, such that women had a downward slope in negative affect as age became higher. The rest of the analyses indicated that men and women were more alike than different in later life, although neuroticism, age, and stress had some notable main effects on affect and cortisol outcomes. These results enhance our understanding of the complex relationship between psychosocial effects and physiological stress responses in an age range rarely studied in the stress and resilience literature. Title: Are There Gender Differences in Stress Response in Older Adults? Findings from the Normative Aging Study Author: Proulx, Jeffrey A. In this study, we explored the relationships among gender, age, daily stressors, positive and negative affect, and neuroticism on cortisol outcomes in older men and women. We were particularly interested in whether variation in positive affect would have an effect on variation in negative affect and if this relationship would mediate the stress process. Further, we were interested in whether women would have lower cortisol outcomes as a result of this process. The participants in this study included 96 men (mean age = 79) and 65 of their wives (mean age = 75) who took part in an at-home 8- day daily diary study as part of the Normative Aging Study (NAS). This study uses data collected on four of those days in which participants provided 4 measures of salivary cortisol that we matched with a NAS version of the Daily Inventory of Stressful Events (DISE; Almeida, Wethington, & Kessler, 2002), PANAS (Watson, Clark, & Tellegen, 1988), and a 2007 assessment of neuroticism (Goldberg, 1992). Bivariate, regression, and three-level MLM-mediated-moderated analyses indicated that age had a significant effect on negative affect reports, but only for women, such that women had a downward slope in negative affect as age became higher. The rest of the analyses indicated that men and women were more alike than different in later life, although neuroticism, age, and stress had some notable main effects on affect and cortisol outcomes. These results enhance our understanding of the complex relationship between psychosocial effects and physiological stress responses in an age range rarely studied in the stress and resilience literature. Close

• 35. [Article] The aging endoplasmic reticulum

  Hallmarks of aging include the accumulation of aberrant proteins and a lower resistance to stresses. Because the endoplasmic reticulum (ER) functions to fold proteins and possesses unique stress sensing ...

  Citation × Citation Citation Abstract Copy Title: The aging endoplasmic reticulum Author: Dixon, Brian M. Hallmarks of aging include the accumulation of aberrant proteins and a lower resistance to stresses. Because the endoplasmic reticulum (ER) functions to fold proteins and possesses unique stress sensing pathways, the central hypothesis of this dissertation is that the ER is a target of cellular aging and significantly underlies these age-related phenotypes. This hypothesis was tested using isolated microsomes from young (3-6 mo) and old (24-26 mo) rats and a novel primary hepatocyte cell culture model that maintains the aging phenotype. The ER luminal oxidation/reduction (redox) environment, exemplified by the glutathione redox ratio (GSH:GSSG), is vital for both ER stress signaling and the regulation of ER oxidoreductase activity. Therefore, the hepatic microsomal GSH:GSSG ratio from young and old rats was determined. Our results showed that the GSH:GSSG ratio in young rats was 3.8:1 and that, in contrast to the age-related loss of GSH redox in whole liver, microsomal GSH:GSSG increased to 6.4:1 in old rats. This increase is sufficient to convert ER oxidoreductases from folding proteins to enzymes involved in protein unfolding. These results show that the ER is under an increased stress with age, yet no activation of ER stress response pathways was detected. Using the aging cell culture model noted above to examine the loss of ER stress response with age, we show that following induction of an ER stress by tunicamycin, ER-mediated "pro-apoptotic" pathways were in intact with age, but induction of "pro-survival" genes were significantly delayed. Taken together, these show that aging leads to: 1) a reductive shift in ER thiol redox, and 2) an attenuation of ER stress response. Lastly, previous work showed that (R)-alpha-lipoic acid (R-LA) restores GSH levels and redox status in aged rat livers. To determine whether R-LA also reversed the age-related changes in ER GSH redox status, young and old rats were supplemented with R-LA. Results showed that R-LA reversed both the age-related increase in the ER GSH redox state and induced protective ER stress response pathways in a manner similar to young animals. Thus, R-LA may be an effective therapeutic to maintain ER homeostatic mechanisms with age. Title: The aging endoplasmic reticulum Author: Dixon, Brian M. Hallmarks of aging include the accumulation of aberrant proteins and a lower resistance to stresses. Because the endoplasmic reticulum (ER) functions to fold proteins and possesses unique stress sensing pathways, the central hypothesis of this dissertation is that the ER is a target of cellular aging and significantly underlies these age-related phenotypes. This hypothesis was tested using isolated microsomes from young (3-6 mo) and old (24-26 mo) rats and a novel primary hepatocyte cell culture model that maintains the aging phenotype. The ER luminal oxidation/reduction (redox) environment, exemplified by the glutathione redox ratio (GSH:GSSG), is vital for both ER stress signaling and the regulation of ER oxidoreductase activity. Therefore, the hepatic microsomal GSH:GSSG ratio from young and old rats was determined. Our results showed that the GSH:GSSG ratio in young rats was 3.8:1 and that, in contrast to the age-related loss of GSH redox in whole liver, microsomal GSH:GSSG increased to 6.4:1 in old rats. This increase is sufficient to convert ER oxidoreductases from folding proteins to enzymes involved in protein unfolding. These results show that the ER is under an increased stress with age, yet no activation of ER stress response pathways was detected. Using the aging cell culture model noted above to examine the loss of ER stress response with age, we show that following induction of an ER stress by tunicamycin, ER-mediated "pro-apoptotic" pathways were in intact with age, but induction of "pro-survival" genes were significantly delayed. Taken together, these show that aging leads to: 1) a reductive shift in ER thiol redox, and 2) an attenuation of ER stress response. Lastly, previous work showed that (R)-alpha-lipoic acid (R-LA) restores GSH levels and redox status in aged rat livers. To determine whether R-LA also reversed the age-related changes in ER GSH redox status, young and old rats were supplemented with R-LA. Results showed that R-LA reversed both the age-related increase in the ER GSH redox state and induced protective ER stress response pathways in a manner similar to young animals. Thus, R-LA may be an effective therapeutic to maintain ER homeostatic mechanisms with age. Close

• 36. [Article] Aging and serum MCP-1 are associated with gut microbiome composition in a murine model

  The following information was supplied regarding data availability: BioProject ID PRJNA311095, accessions SRX1581953, SRX1581958-RX1581960, and SRX1571787-RX1571792 http://files.cgrb.oregonstate.edu/Sh...

  Citation × Citation Citation Abstract Copy Title: Aging and serum MCP-1 are associated with gut microbiome composition in a murine model Author: Conley, Melissa N., Ho, Emily, Duyck, Kyle M., Hord, Norman, Wong, Carmen P., Sharpton, Thomas J. The following information was supplied regarding data availability: BioProject ID PRJNA311095, accessions SRX1581953, SRX1581958-RX1581960, and SRX1571787-RX1571792 http://files.cgrb.oregonstate.edu/Sharpton_Lab/Papers/Conley_PeerJ_2015/ Title: Aging and serum MCP-1 are associated with gut microbiome composition in a murine model Author: Conley, Melissa N., Ho, Emily, Duyck, Kyle M., Hord, Norman, Wong, Carmen P., Sharpton, Thomas J. The following information was supplied regarding data availability: BioProject ID PRJNA311095, accessions SRX1581953, SRX1581958-RX1581960, and SRX1571787-RX1571792 http://files.cgrb.oregonstate.edu/Sharpton_Lab/Papers/Conley_PeerJ_2015/ Close

• 37. [Article] Influence of landscape-scale variables on the age and growth of coastal cutthroat trout Oncorhynchus clarkii clarkii in headwater streams

  This thesis provides the first general description of the natural variation in age structure, growth rates, and survival in headwater populations of coastal cutthroat trout Oncorhynchus clarkii clarkii ...

  Citation × Citation Citation Abstract Copy Title: Influence of landscape-scale variables on the age and growth of coastal cutthroat trout Oncorhynchus clarkii clarkii in headwater streams Author: Rehe, William G. This thesis provides the first general description of the natural variation in age structure, growth rates, and survival in headwater populations of coastal cutthroat trout Oncorhynchus clarkii clarkii from western Oregon, and a subsequent synthesis of these life-history characteristics across the range of the subspecies. Age, growth, and survival were estimated by analyzing scales from 4,250 fish collected from 37 headwater watersheds in western Oregon from 1999 to 2001. Age was validated for 234 marked and recaptured coastal cutthroat trout from two watersheds, and >94% of the scales exhibited the expected number of annuli between capture dates. Variation among readings was low (< 9%), and there was only a slight bias between readings for older fish (primarily age-5 fish). Missing first-year annuli, often observed in cutthroat trout subspecies, were not observed for these populations. Mean relative growth rates decreased with age and size. In three populations maximum age was 3 years, but in the majority, maximum age was 4 (24 populations) or 5 years (8 populations). Annual survival rates of age-3 coastal cutthroat trout (i.e., between age-2 and age-3) ranged from 23% to 65%. Akaike's Information Criterion (AIC) was used to select multiple regression models that "best" described biological response (i.e., length at age-1, mean length, and survival) to physical habitat variables. The model with January water temperature and calcium ions as predictor variables was the "best approximating model" for predicting mean length at age 1. The model with maximum pool depth and stream channel connectivity was most useful for predicting mean fish length in a watershed, and mean survival was best predicted by a model with mean July water temperature and maximum pool depth as predictor variables. Summary of range-wide life-history data for coastal cutthroat trout suggests that patterns in growth, age, and length do not follow a generalized geographic trend from north to south, and at least some differences appear to be related to life-history type. Title: Influence of landscape-scale variables on the age and growth of coastal cutthroat trout Oncorhynchus clarkii clarkii in headwater streams Author: Rehe, William G. This thesis provides the first general description of the natural variation in age structure, growth rates, and survival in headwater populations of coastal cutthroat trout Oncorhynchus clarkii clarkii from western Oregon, and a subsequent synthesis of these life-history characteristics across the range of the subspecies. Age, growth, and survival were estimated by analyzing scales from 4,250 fish collected from 37 headwater watersheds in western Oregon from 1999 to 2001. Age was validated for 234 marked and recaptured coastal cutthroat trout from two watersheds, and >94% of the scales exhibited the expected number of annuli between capture dates. Variation among readings was low (< 9%), and there was only a slight bias between readings for older fish (primarily age-5 fish). Missing first-year annuli, often observed in cutthroat trout subspecies, were not observed for these populations. Mean relative growth rates decreased with age and size. In three populations maximum age was 3 years, but in the majority, maximum age was 4 (24 populations) or 5 years (8 populations). Annual survival rates of age-3 coastal cutthroat trout (i.e., between age-2 and age-3) ranged from 23% to 65%. Akaike's Information Criterion (AIC) was used to select multiple regression models that "best" described biological response (i.e., length at age-1, mean length, and survival) to physical habitat variables. The model with January water temperature and calcium ions as predictor variables was the "best approximating model" for predicting mean length at age 1. The model with maximum pool depth and stream channel connectivity was most useful for predicting mean fish length in a watershed, and mean survival was best predicted by a model with mean July water temperature and maximum pool depth as predictor variables. Summary of range-wide life-history data for coastal cutthroat trout suggests that patterns in growth, age, and length do not follow a generalized geographic trend from north to south, and at least some differences appear to be related to life-history type. Close

• 38. [Article] An Accumulation of Senescent Cells May Contribute to Chronic Inflammation of the Mammalian Liver

  The aging process is a biological phenomenon in mammals that heavily contributes to the onset of chronic diseases. While there are many theories that attempt to explain the biological onset of aging, one ...

  Citation × Citation Citation Abstract Copy Title: An Accumulation of Senescent Cells May Contribute to Chronic Inflammation of the Mammalian Liver Author: Sugiyama, Aaron The aging process is a biological phenomenon in mammals that heavily contributes to the onset of chronic diseases. While there are many theories that attempt to explain the biological onset of aging, one emerging theory involves chronic inflammation. Chronic inflammation has been previously linked to several age-related diseases and is a known driver of chronic inflammation. To examine chronic inflammation and cellular senescence in the context of aging, we examined hepatocytes harvested from rat livers as a model. We found that rat hepatocytes not only undergo cellular senescence, but that senescent cells accumulate with age. This accumulation of senescent cells with age was also accompanied by a large increase in miR-146a and miR-155 (a seven fold and a forty-five fold change respectively) in the old rat exosomes, which indicate chronic inflammatory insult. These findings corroborate with our findings regarding an accumulation of senescent cells in the liver, and suggests that the liver undergoes an inflammatory stress. We then examined a possible treatment for cellular senescence: the drug known as dasatinib. Title: An Accumulation of Senescent Cells May Contribute to Chronic Inflammation of the Mammalian Liver Author: Sugiyama, Aaron The aging process is a biological phenomenon in mammals that heavily contributes to the onset of chronic diseases. While there are many theories that attempt to explain the biological onset of aging, one emerging theory involves chronic inflammation. Chronic inflammation has been previously linked to several age-related diseases and is a known driver of chronic inflammation. To examine chronic inflammation and cellular senescence in the context of aging, we examined hepatocytes harvested from rat livers as a model. We found that rat hepatocytes not only undergo cellular senescence, but that senescent cells accumulate with age. This accumulation of senescent cells with age was also accompanied by a large increase in miR-146a and miR-155 (a seven fold and a forty-five fold change respectively) in the old rat exosomes, which indicate chronic inflammatory insult. These findings corroborate with our findings regarding an accumulation of senescent cells in the liver, and suggests that the liver undergoes an inflammatory stress. We then examined a possible treatment for cellular senescence: the drug known as dasatinib. Close

• 39. [Article] Women's alcohol consumption : personal, familial, and geopolitical dimensions

  A sample of 1,003 women, age 22 in 1983-84 and age 27 in 1988-89, were selected from the National Longitudinal Survey of Youth. Personal, familial, and geopolitical predictors of alcohol consumption were ...

  Citation × Citation Citation Abstract Copy Title: Women's alcohol consumption : personal, familial, and geopolitical dimensions Author: Goetz, Kathryn W. A sample of 1,003 women, age 22 in 1983-84 and age 27 in 1988-89, were selected from the National Longitudinal Survey of Youth. Personal, familial, and geopolitical predictors of alcohol consumption were evaluated at each time period and longitudinally. The study integrated macro- and micro-level influences to determine their influence on individual alcohol consumption. Personal and familial were most influential. Availability of alcohol and political economy had little effect on consumption. Mother's history of alcohol abuse was more important than father's. At age 22 education, being married, and having children reduced consumption, as did a prior affiliation with a religion that proscribed the use of alcohol reduced consumption. At age 27 education, being married, and children decreased consumption, but religious affiliation and parent's consumption were not significant. While marital status at age 22 reduced drinking at that age, it lead to greater consumption at age 27. Title: Women's alcohol consumption : personal, familial, and geopolitical dimensions Author: Goetz, Kathryn W. A sample of 1,003 women, age 22 in 1983-84 and age 27 in 1988-89, were selected from the National Longitudinal Survey of Youth. Personal, familial, and geopolitical predictors of alcohol consumption were evaluated at each time period and longitudinally. The study integrated macro- and micro-level influences to determine their influence on individual alcohol consumption. Personal and familial were most influential. Availability of alcohol and political economy had little effect on consumption. Mother's history of alcohol abuse was more important than father's. At age 22 education, being married, and having children reduced consumption, as did a prior affiliation with a religion that proscribed the use of alcohol reduced consumption. At age 27 education, being married, and children decreased consumption, but religious affiliation and parent's consumption were not significant. While marital status at age 22 reduced drinking at that age, it lead to greater consumption at age 27. Close

• 40. [Article] Impact of asset usage preferences on parallel replacement decisions

  Data from a state department of transportation fleet shows that the usage of a typical asset decreases as it ages. One possible explanation for decreasing asset usage with age is operator preference for ...

  Citation × Citation Citation Abstract Copy Title: Impact of asset usage preferences on parallel replacement decisions Author: Wagner, Tristan John Data from a state department of transportation fleet shows that the usage of a typical asset decreases as it ages. One possible explanation for decreasing asset usage with age is operator preference for using the newest available asset. In this research the long-term cost and replacement implications of such a "newest first" usage practice are investigated for a fleet of similar assets with a fixed replacement age (age standard). Capital constraints on replacement are not considered. Comparisons are made to a "random" usage practice that results in constant expected usage as an asset ages. For most major cost categories, the newest first usage practice results in greater or equal costs. It is also shown that asset usage and fixed replacement age are interdependent under the newest first usage practice. The implications of this are that simple approaches found in the literature to address decreasing usage with age give incorrect results. Title: Impact of asset usage preferences on parallel replacement decisions Author: Wagner, Tristan John Data from a state department of transportation fleet shows that the usage of a typical asset decreases as it ages. One possible explanation for decreasing asset usage with age is operator preference for using the newest available asset. In this research the long-term cost and replacement implications of such a "newest first" usage practice are investigated for a fleet of similar assets with a fixed replacement age (age standard). Capital constraints on replacement are not considered. Comparisons are made to a "random" usage practice that results in constant expected usage as an asset ages. For most major cost categories, the newest first usage practice results in greater or equal costs. It is also shown that asset usage and fixed replacement age are interdependent under the newest first usage practice. The implications of this are that simple approaches found in the literature to address decreasing usage with age give incorrect results. Close