Are the Steps on Likert Scales Equidistant? Responses on Visual Analog Scales Allow Estimating Their Distances.

A recurring question regarding Likert items is whether the discrete steps that this response format allows represent constant increments along the underlying continuum. This question appears unsolvable because Likert responses carry no direct information to this effect. Yet, any item administered in Likert format can identically be administered with a continuous response format such as a visual analog scale (VAS) in which respondents mark a position along a continuous line. Then, the operating characteristics of the item would manifest under both VAS and Likert formats, although perhaps differently as captured by the continuous response model (CRM) and the graded response model (GRM) in item response theory. This article shows that CRM and GRM item parameters hold a formal relation that is mediated by the form in which the continuous dimension is partitioned into intervals to render the discrete Likert responses. Then, CRM and GRM characterizations of the items in a test administered with VAS and Likert formats allow estimating the boundaries of the partition that renders Likert responses for each item and, thus, the distance between consecutive steps. The validity of this approach is first documented via simulation studies. Subsequently, the same approach is used on public data from three personality scales with 12, eight, and six items, respectively. The results indicate the expected correspondence between VAS and Likert responses and reveal unequal distances between successive pairs of Likert steps that also vary greatly across items. Implications for the scoring of Likert items are discussed.

Both reduced ovarian reserve and severe semen alterations are overrepresented in couples seeking assisted reproductive technology treatment for the first time: a cross-sectional study.

BACKGROUND: Once a mate choice decision has been made, couples that fail to reach a live birth in natural and/or intrauterine insemination (IUI) cycles will likely visit fertility clinics seeking assisted reproductive technology (ART) treatment. During the more or less prolonged period of infertility experienced, those couples with mild/moderate reproductive anomalies would have advantage over couples displaying more severe reproductive alterations in achieving a natural or IUI conception. Thus, we can expect to find a progressive increase in the proportion of couples with more severe reproductive anomalies as duration of infertility rises. In this study, we aim to ascertain whether there is an association between male and female infertility diagnoses and duration of infertility in couples seeking ART treatment for the first time. METHODS: A cross-sectional analysis of 1383 infertile couples that sought ART treatment for the first time. Forward-stepwise binary logistic regression analyses were applied to calculate exponentiated regression coefficients. RESULTS: Men suffering from any combination of oligo-, astheno-, and teratozoospermia (ACOAT) exhibited higher odds of having a duration of infertility > 2 years compared with non-ACOAT men [odds ratio (95% confidence interval): 1.340 (1.030-1.744)]. Women from ACOAT couples displaying a duration of infertility > 2 years presented shorter menstrual cycles (P ≤ 0.047) and lower antral follicular count (AFC) values (P ≤ 0.008) and serum anti-Müllerian hormone (AMH) levels (P ≤ 0.007) than women from non-ACOAT couples exhibiting > 2 years of infertility. Likewise, AFC values (P ≤ 0.013) and serum AMH levels (P ≤ 0.001) were decreased when compared with women from ACOAT couples displaying ≤ 2 years of infertility. A relative low but significant percentage of ACOAT couples displaying > 2 years of infertility stood out for their smoking habits. CONCLUSIONS: Couples consisting of ACOAT men and women with a relative low ovarian reserve are overrepresented in couples seeking ART treatment for the first time after experiencing > 2 years of infertility. This outcome leads us to develop a general hypothesis proposing that the origin of couple's infertility is a consequence of a process of positive assortative mating shaped by sexual selection forces.

Accuracy and precision of responses to visual analog scales: Inter- and intra-individual variability.

Visual analog scales (VASs) are gaining popularity for collecting responses in computer administration of psychometric tests and surveys. The VAS format consists of a line marked at its endpoints with the minimum and maximum positions that it covers for respondents to place a mark at their selected location. Creating the line with intermediate marks along its length was discouraged, but no empirical evidence has ever been produced to show that their absence does any good. We report a study that asked respondents to place marks at pre-selected locations on a 100-unit VAS line, first when it only had numerical labels (0 and 100) at its endpoints and then when intermediate locations (from 0 to 100 in steps of 20) were also labeled. The results show that settings are more accurate and more precise when the VAS line has intermediate tick marks: The average absolute error decreased from 3.02 units without intermediate marks to 0.82 units with them. Provision of intermediate tick marks also reduced substantially inter- and intra-individual variability in accuracy and precision: The standard deviation of absolute error decreased from 0.87 units without tick marks to 0.25 units with them and the standard deviation of signed distance to target decreased from 1.16 units without tick marks to 0.24 units with them. These results prompt the recommendation that the design of VASs includes intermediate tick marks along the length of the line.

It Is Premature to Use Postmortem Sperm for Reproductive Purposes: a Data-Driven Opinion.

Postmortem sperm retrieval for reproductive purposes is an assisted reproduction procedure that offers women an opportunity to have a child using sperm retrieved from their deceased partners. The ethical issues of this procedure have been discussed in previous works. However, an assessment of the procedure using a scientific perspective is still lacking. Here, we aim to ascertain, using a biological standpoint, whether postmortem sperm should be rescued for reproductive purposes. Data suggest that it is premature to use postmortem sperm for reproductive purposes. This procedure should not be clinically applied until appropriate and comprehensive analyses have been completed. Such analyses should be focused not only on fertilization, embryo development, and pregnancy outcomes, but also on potential postmortem alterations of sperm DNA, RNAs, and proteins. In addition, genetic and epigenetic analyses of sperm, pre-implantation embryos, and newborns, as well as mental and physical health follow-up of the resulting offspring during a whole life cycle, using appropriate non-human mammalian models, are warranted.

Order effects in two-alternative forced-choice tasks invalidate adaptive threshold estimates.

Adaptive psychophysical methods are widely used for the quick estimation of percentage points (thresholds) on psychometric functions for two-alternative forced-choice (2AFC) tasks. The use of adaptive methods is supported by numerous simulation studies documenting their performance, which have shown that thresholds can be reasonably estimated with them when their founding assumptions hold. One of these assumptions is that the psychometric function is invariant, but empirical evidence is mounting that human performance in 2AFC tasks needs to be described by two different psychometric functions, one that holds when the test stimulus is presented first in the 2AFC trial and a different one that holds when the test is presented second. The same holds when presentations are instead simultaneous at two spatial locations rather than sequential. We re-evaluated the performance of adaptive methods in the presence of these order effects via simulation studies and an empirical study with human observers. The simulation study showed that thresholds are severely overestimated by adaptive methods in these conditions, and the empirical study corroborated these findings. These results question the validity of threshold estimates obtained with adaptive methods that incorrectly assume the psychometric function to be invariant with presentation order. Alternative ways in which thresholds can be accurately estimated in the presence of order effects are discussed.

Predictors of live birth in women with a history of biochemical pregnancies after assisted reproduction treatment.

OBJECTIVES: To ascertain whether women with a history of biochemical pregnancies (BPs) in in-vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) treatment cycles have decreased chances of live birth (LB); and (2) to build a predictive model for LB in this particular population of infertile women. METHODS: In order to achieve the first objective, data from 1536 women that had a LB using autologous fresh or frozen embryos, or dropped out of further IVF/ICSI treatments after completing one to three unsuccessful treatment cycles were retrospectively analyzed. A subpopulation of 90 women that experienced one or more BPs in our assisted reproduction unit were selected to build a predictive logistic regression model for LB. RESULTS: LB percentages significantly decreased from a value of 55.3 % in women with no history of previous BPs to 30.9 % and 11.1 % in women that displayed a history of one or more than one BP, respectively. Three out of 35 selected potential predictors were finally included into the model: "number of the last embryo transfer cycle resulting in a BP", "women's age", and "oligo-, astheno-, and/or teratozoospermia". The value of the c-statistic was 0.819 (asymptotic 95 % CI: 0.724-0.913). The model adequately fitted the data with no significant over or underestimation of predictor effects. CONCLUSION: (1) A history of BPs is negatively associated with later chance of LB in women undergoing a series of IVF/ICSI treatment cycles; and (2) LB probability of women with a history of BPs can be predicted using a model with excellent discriminatory capacity.

Asymptotic versus exact methods in the analysis of contingency tables: Evidence-based practical recommendations.

Controversy over the validity of significance tests in the analysis of contingency tables is motivated by the disagreement between asymptotic and exact p values and its dependence on the magnitude of expected frequencies. Variants of Pearson's X2 statistic and their asymptotic distributions were proposed to overcome the difficulties, but several approaches also exist to conduct exact tests. This paper shows that discrepant asymptotic and exact results may or may not occur whether expected frequencies are large or small: Eventual inaccuracy of asymptotic p values is instead caused by idiosyncrasies of the discrete distribution of X2. More importantly, discrepancies are also artificially created by the hypergeometric sampling model used to perform exact tests. Exact computations under the alternative full-multinomial or product-multinomial models require eliminating nuisance parameters and we propose a novel method that integrates them out. The resultant exact distributions are very accurately approximated by the asymptotic distribution, which eliminates concerns about the accuracy of the latter. We also discuss that the two-stage approach that tests for significance of residuals conditional on a significant X2 test is inadvisable and that an alternative single-stage test preserves Type-I error rates and further eliminates concerns about asymptotic accuracy.

Correction to: a predictive model for women's assisted fecundity before starting the first IVF/ICSI treatment cycle.

The original article unfortunately contained a mistake. In Table 2, the headers "Development set" and "Validation set" were not aligned to to their sub-headers.

Cumulative probabilities of live birth across multiple complete IVF/ICSI cycles: a call for attention.

PURPOSE: To call attention to the fact that cumulative live birth (LB) proportions exhibit an inverted pattern to that displayed by each individual oocyte retrieval cycle (ORC-specific LB proportions) as well as when grouping together all the ORCs undergone by a woman (TNORC-specific LB proportions). METHODS: A retrospective study of 1433 infertile women that had a LB using autologous fresh or frozen embryos and/or dropped out of IVF/ICSI treatment after completing a maximum number of three treatment cycles. Generalized Estimating Equations (GEE) and standard and landmark Kaplan-Meier survival analyses were applied. RESULTS: A standard Kaplan-Meier analysis indicated that cumulative LB proportions rose as number of ORCs increased (0.320, 0.484, and 0.550 at ORC 1, 2, and 3, respectively). In contrast, landmark ORC-specific LB proportions showed an inverted pattern (0.320, 0.242, and 0.127 at ORC 1, 2, and 3, respectively). GEE models revealed that women's clinical outcomes decreased as TNORCs increased. In particular, compared to women that experienced just one ORC, women that underwent two and three ORCs displayed higher incidences of cycle cancellations before either oocyte retrieval or embryo transfer, and clinical pregnancy losses, and lower odds of LB. CONCLUSION: Infertile women should be informed that cumulative LB probabilities exhibit an inverted pattern to that displayed by each individual ORC as well as when grouping together all the ORCs undergone by a woman.

A predictive model for women's assisted fecundity before starting the first IVF/ICSI treatment cycle.

PURPOSE: To introduce a prognostic model for women's assisted fecundity before starting the first IVF/ICSI treatment cycle. METHODS: In contrast to previous predictive models, we analyze two groups of women at the extremes of prognosis. Specifically, 708 infertile women that had either a live birth (LB) event in the first autologous IVF/ICSI cycle ("high-assisted-fecundity women", n = 458) or did not succeed in having a LB event after completing three autologous IVF/ICSI cycles ("low-assisted-fecundity women", n = 250). The initial sample of 708 women was split into two sets in order to develop (n = 531) and internally validate (n = 177) a predictive logistic regression model using a forward-stepwise variable selection. RESULTS: Seven out of 32 initially selected potential predictors were included into the model: women's age, presence of multiple female infertility factors, number of antral follicles, women's tobacco smoking, occurrence of irregular menstrual cycles, and basal levels of prolactin and LH. The value of the c-statistic was 0.718 (asymptotic 95% CI 0.672-0.763) in the development set and 0.649 (asymptotic 95% CI: 0.560-0.738) in the validation set. The model adequately fitted the data with no significant over or underestimation of predictor effects. CONCLUSION: Women's assisted fecundity may be predicted using a relatively small number of predictors. This approach may complement the traditional procedure of estimating cumulative and cycle-specific probabilities of LB across multiple complete IVF/ICSI cycles. In addition, it provides an easy-to-apply methodology for fertility clinics to develop and actualize their own predictive models.

Psychophysical Tests Do Not Identify Ocular Dominance Consistently.

Classical sighting or sensory tests are used in clinical practice to identify the dominant eye. Several psychophysical tests were recently proposed to quantify the magnitude of dominance but whether their results agree was never investigated. We addressed this question for the two most common psychophysical tests: The perceived-phase test, which measures the cyclopean appearance of dichoptically presented sinusoids of different phase, and the coherence-threshold test, which measures interocular differences in motion perception when signal and noise stimuli are presented dichoptically. We also checked for agreement with three classical tests (Worth 4-dot, Randot suppression, and Bagolini lenses). Psychophysical tests were administered in their conventional form and also using more dependable psychophysical methods. The results showed weak correlations between psychophysical measures of strength of dominance with inconsistent identification of the dominant eye across tests: Agreement on left-eye dominance, right-eye dominance, or nondominance by both tests occurred only for 11 of 40 observers (27.5%); the remaining 29 observers were classified differently by each test, including 14 cases (35%) of opposite classification (left-eye dominance by one test and right-eye dominance by the other). Classical tests also yielded conflicting results that did not agree well with classification based on psychophysical tests. The results are discussed in the context of determination of ocular dominance for clinical decisions.

Nonparametric tests for equality of psychometric functions.

Many empirical studies measure psychometric functions (curves describing how observers' performance varies with stimulus magnitude) because these functions capture the effects of experimental conditions. To assess these effects, parametric curves are often fitted to the data and comparisons are carried out by testing for equality of mean parameter estimates across conditions. This approach is parametric and, thus, vulnerable to violations of the implied assumptions. Furthermore, testing for equality of means of parameters may be misleading: Psychometric functions may vary meaningfully across conditions on an observer-by-observer basis with no effect on the mean values of the estimated parameters. Alternative approaches to assess equality of psychometric functions per se are thus needed. This paper compares three nonparametric tests that are applicable in all situations of interest: The existing generalized Mantel-Haenszel test, a generalization of the Berry-Mielke test that was developed here, and a split variant of the generalized Mantel-Haenszel test also developed here. Their statistical properties (accuracy and power) are studied via simulation and the results show that all tests are indistinguishable as to accuracy but they differ non-uniformly as to power. Empirical use of the tests is illustrated via analyses of published data sets and practical recommendations are given. The computer code in MATLAB and R to conduct these tests is available as Electronic Supplemental Material.

Order-Constrained Estimation of Nominal Response Model Parameters to Assess the Empirical Order of Categories.

Bock's nominal response model (NRM) is sometimes used to identify the empirical order of response categories in polytomous items but its application tags many items as having disordered categories. Disorderly estimated categories may not reflect a true characteristic of the items but, rather, a numerically best-fitting solution possibly equivalent to other solutions with orderly estimated categories. To investigate this possibility, an order-constrained variant of the NRM was developed that enforces the preassumed order of categories on parameter estimates, for a comparison of its outcomes with those of the original unconstrained NRM. For items with ordered categories, order-constrained and unconstrained solutions should account for the data equally well even if the latter solution estimated disordered categories for some items; for items with truly disordered categories, the unconstrained solution should outperform the order-constrained solution. Criteria for this comparative analysis are defined and their utility is tested in several simulation studies with items of diverse characteristics, including ordered and disordered categories. The results demonstrate that a comparison of order-constrained and unconstrained calibrations on such criteria provides the evidence needed to determine whether category disorder estimated on some items by the original unconstrained form of the NRM is authentic or spurious. Applications of this method to assess category order in existing data sets are presented and practical implications are discussed.

Note of clarification: Potential risks to offspring of intrauterine exposure to maternal age-related obstetric complications.

Several hypotheses have been proposed to explain the negative effects of delayed motherhood on an offspring's morbidity later in life. However, these hypotheses are not supported by clinical and epidemiological evidence. Because advanced maternal age is associated with increased risk of obstetric complications, the aim of the present study was to ascertain whether the negative effects on offspring of intrauterine exposure to maternal age-related obstetric complications may explain the reported negative effects of delayed motherhood on offspring. To this end, a literature search was performed to identify relevant publications up to March 2016 on PubMed; references cited in relevant articles were also searched. There was a direct correlation between the risks to offspring conferred by intrauterine exposure to at least one of the obstetric complications present at the time of delivery in women aged ≥35 years and the risks to offspring of delayed motherhood. This correlation was not observed when comparing the risks to offspring of delayed motherhood and the risks associated with maternal transmission of defective mitochondria, chromosomal anomalies or DNA double-strand breaks. Most of the effects on offspring of intrauterine exposure to maternal age-related obstetric complications may be induced by epigenetic DNA reprogramming during critical periods of embryo or fetal development. Women wanting to enrol in a fertility preservation program to offset age-related declines in fertility should be informed not only about their chances of pregnancy and the percentage of live births, but also about the risks to themselves and their prospective offspring of delaying motherhood.

The Indecision Model of Psychophysical Performance in Dual-Presentation Tasks: Parameter Estimation and Comparative Analysis of Response Formats.

Psychophysical data from dual-presentation tasks are often collected with the two-alternative forced-choice (2AFC) response format, asking observers to guess when uncertain. For an analytical description of performance, psychometric functions are then fitted to data aggregated across the two orders/positions in which stimuli were presented. Yet, order effects make aggregated data uninterpretable, and the bias with which observers guess when uncertain precludes separating sensory from decisional components of performance. A ternary response format in which observers are also allowed to report indecision should fix these problems, but a comparative analysis with the 2AFC format has never been conducted. In addition, fitting ternary data separated by presentation order poses serious challenges. To address these issues, we extended the indecision model of psychophysical performance to accommodate the ternary, 2AFC, and same-different response formats in detection and discrimination tasks. Relevant issues for parameter estimation are also discussed along with simulation results that document the superiority of the ternary format. These advantages are demonstrated by fitting the indecision model to published detection and discrimination data collected with the ternary, 2AFC, or same-different formats, which had been analyzed differently in the sources. These examples also show that 2AFC data are unsuitable for testing certain types of hypotheses. matlab and R routines written for our purposes are available as Supplementary Material, which should help spread the use of the ternary format for dependable collection and interpretation of psychophysical data.

An Analysis of (Dis)Ordered Categories, Thresholds, and Crossings in Difference and Divide-by-Total IRT Models for Ordered Responses.

Threshold parameters have distinct referents across models for ordered responses. In difference models, thresholds are trait levels at which responding beyond category k is as likely as responding at or below it; in divide-by-total models, thresholds are trait levels at which responding in category k is as likely as responding in category k - 1. Thus, thresholds in divide-by-total models (but not in difference models) are the crossings of the option response functions for consecutive categories. Thresholds in difference models are always ordered but they may inconsequentially yield ordered or disordered crossings. In contrast, assimilation of thresholds and crossings in divide-by-total models questions category order when crossings are disordered. We analyze these aspects of difference and divide-by-total models, their relation to the order of response categories, and the consequences of collapsing categories to instate ordered crossings under divide-by-total models. We also show that item parameters in models for ordered responses can never contradict the pre-assumed order of categories and that the empirical order can only be established using a polytomous model that does not assume ordered categories, although this often gives rise to spurious outcomes. Practical implications for scale development are discussed.

Potential risks to offspring of intrauterine exposure to maternal age-related obstetric complications.

Several hypotheses have been proposed to explain the negative effects of delayed motherhood on an offspring's morbidity later in life. However, these hypotheses are not supported by clinical and epidemiological evidence. Because advanced maternal age is associated with increased risk of obstetric complications, the aim of the present study was to ascertain whether the negative effects on offspring of intrauterine exposure to maternal age-related obstetric complications may explain the reported negative effects of delayed motherhood on offspring. To this end, a literature search was performed to identify relevant publications up to March 2016 on PubMed; references cited in relevant articles were also searched. There was a direct correlation between the risks to offspring conferred by intrauterine exposure to at least one of the obstetric complications present at the time of delivery in women aged ≥35 years and the risks to offspring of delayed motherhood. This correlation was not observed when comparing the risks to offspring of delayed motherhood and the risks associated with maternal transmission of defective mitochondria, chromosomal anomalies or DNA double-strand breaks. Most of the effects on offspring of intrauterine exposure to maternal age-related obstetric complications may be induced by epigenetic DNA reprogramming during critical periods of embryo or fetal development. Women wanting to enrol in a fertility preservation program to offset age-related declines in fertility should be informed not only about their chances of pregnancy and the percentage of live births, but also about the risks to themselves and their prospective offspring of delaying motherhood.

Thou Shalt Not Bear False Witness Against Null Hypothesis Significance Testing.

Null hypothesis significance testing (NHST) has been the subject of debate for decades and alternative approaches to data analysis have been proposed. This article addresses this debate from the perspective of scientific inquiry and inference. Inference is an inverse problem and application of statistical methods cannot reveal whether effects exist or whether they are empirically meaningful. Hence, raising conclusions from the outcomes of statistical analyses is subject to limitations. NHST has been criticized for its misuse and the misconstruction of its outcomes, also stressing its inability to meet expectations that it was never designed to fulfil. Ironically, alternatives to NHST are identical in these respects, something that has been overlooked in their presentation. Three of those alternatives are discussed here (estimation via confidence intervals and effect sizes, quantification of evidence via Bayes factors, and mere reporting of descriptive statistics). None of them offers a solution to the problems that NHST is purported to have, all of them are susceptible to misuse and misinterpretation, and some bring around their own problems (e.g., Bayes factors have a one-to-one correspondence with p values, but they are entirely deprived of an inferential framework). Those alternatives also fail to cover a broad area of inference not involving distributional parameters, where NHST procedures remain the only (and suitable) option. Like knives or axes, NHST is not inherently evil; only misuse and misinterpretation of its outcomes needs to be eradicated.

An analysis of (dis)ordered categories, thresholds, and crossings in difference and divide-by-total IRT model for ordered responses

Threshold parameters have distinct referents across models for ordered responses. In difference models, thresholds are trait levels at which responding beyond category k is as likely as responding at or below it; in divide-by-total models, thresholds are trait levels at which responding in category k is as likely as responding in category k - 1. Thus, thresholds in divide-by-total models (but not in difference models) are the crossings of the option response functions for consecutive categories. Thresholds in difference models are always ordered but they may inconsequentially yield ordered or disordered crossings. In contrast, assimilation of thresholds and crossings in divide-by-total models questions category order when crossings are disordered. We analyze these aspects of difference and divide-by-total models, their relation to the order of response categories, and the consequences of collapsing categories to instate ordered crossings under divide-by-total models. We also show that item parameters in models for ordered responses can never contradict the pre-assumed order of categories and that the empirical order can only be established using a polytomous model that does not assume ordered categories, although this often gives rise to spurious outcomes. Practical implications for scale development are discussed (AU)

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Obstetric and offspring risks of women's morbid conditions linked to prior anticancer treatments.

BACKGROUND: Literature shows the effects of type of cancer and/or anticancer treatment on live birth percentages and/or pregnancy and neonatal complications in female cancer survivors. However, studies analyzing the obstetric and offspring risks of the morbid conditions associated with previous anti-cancer treatments are missing. The present review aims to uncover these risks. METHODS: A literature search based on publications up to March 2016 identified by PubMed and references cited in relevant articles. RESULTS: The morbid conditions associated with prior anticancer treatments including chemotherapy, radiotherapy, surgery, and/or hematopoietic stem-cell transplant may induce not only obstetric and neonatal complications but also long-term effects on offspring. Whereas some risks are predominantly evidenced in untreated women others are observed in both treated and untreated women. These risks may be superimposed on those induced by the current women's trend in Western societies to postpone maternity. CONCLUSIONS: Medical professionals should be aware and inform female cancer survivors wishing to have a child not only of the short- and long-term risks to themselves and their prospective offspring of previous anticancer treatments, fertility-preservation technologies, and pregnancy itself, but also of those risks linked to the morbid conditions induced by prior anticancer treatments. Once female cancer survivors wishing to have a child have been properly informed about the risks of reproduction, they will be best placed to make decisions of whether or not to have a biological or donor-conceived child. In addition, when medical professionals be aware of these risks, they will be also best placed to provide appropriate treatments before/during pregnancy in order to prevent or alleviate the impact of these morbid conditions on maternal and offspring health.