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PubMed1987

Polychotomous logistic regression methods for matched case-control studies with multiple case or control groups.

Two statistical methods, a polychotomous and pairwise approach, are presented to derive estimates of the relative odds in a matched case-control design when multiple case or control groups are used. Test statistics are derived to determine if the relative odds between groups are different. The polychotomous method is limited to case-control sets, i.e., where data are available on all members of a matched set. In contrast, the pairwise method makes use of data from both complete and incomplete sets. Nonetheless, efficiency calculations show that the polychotomous logistic regression model is more efficient even when 40 per cent of the case-control sets are incomplete. An example using a single dichotomous variable is provided.

Adolescent↗
PubMed2006

Association of HLA-DR and -DQ genes with narcolepsy in Koreans: comparison with two control groups, randomly selected subjects and DRB1*1501-DQB1*0602--positive subjects.

The purpose of this study was to investigate the association of human leukocyte antigen (HLA) class II alleles with narcolepsy-cataplexy susceptibility in Koreans. The distribution of HLA-DRB1 and -DQB1 alleles and presence or absence of DRB3/4/5 alleles were examined in 60 narcoleptic patients with clear-cut cataplexy, and the results were compared with two groups of healthy controls: 200 randomly selected controls and 144 DRB1*1501-DQB1*0602 positive controls. All of the narcoleptic patients were DRB1*1501 and DQB1*0602 positive, and their frequencies were significantly higher in patients than in random controls (100% vs 17.0%, p(c) = 2.3 x 10(-30), OR = 583.96; 100% vs 16.5%, p(c) = 3.9 x 10(-31), OR = 605.00). The HLA association in Koreans was as tight as that reported in Japanese. Several DRB1 (*0101, *0405, *0901) and DQB1 alleles (*0303, *0401, *0501, *0601, *0604) were found to have weak protective effects against narcolepsy. DRB4 showed strong protective effect, and this was also significant when compared with DRB1*1501-DQB1*0602 positive controls (18.3% vs 44.4%, p(c) = 0.001, OR = 0.28). DRB3 (OR = 1.86) and DQB1*0301 (OR = 2.45) were found to have weak predisposing effect, when compared with DRB1*1501-DQB1*0602 positive controls. The protective effect of DRB4 has to be further studied in other populations.

Adolescent↗
PubMed1994

Secretory pattern of vasopressin in plasma and cerebrospinal fluid of patients with dementia and of two control groups.

Since the description of its antidiuretic effect in 1913, a variety of functions have been attributed to vasopressin, one of the most controversial throughout the years probably being its effect on memory processes. In an attempt to study the actual secretory rhythm of vasopressin in humans with demonstrated impaired memory, the plasma and cerebrospinal fluid levels of the peptide have been examined during 24 h in a group of patients with dementia, and their values compared with two healthy control groups of young and elderly volunteers. Patients with dementia had higher circulating levels of vasopressin in plasma than the healthy participants and the differences were statistically significant when compared with the healthy elderly (p = 0.003). This difference is not age-related because both groups were in the same age range. A possible explanation could be the higher plasma osmolality measured in the patients with dementia, despite the fact that their levels were within the normal ranges. The different results could not be attributed to changes in electrolytes or blood pressure because these parameters were similar in all groups (p = NS). But more interesting, perhaps, is the secretory pattern found in all three groups. The pattern is biphasic, with two significant peaks: at 16.00 h (p = 0.032) and at night (p = 0.002). This pattern was similar in all cases and in all groups. The total nocturnal secretion of vasopressin is higher than the diurnal secretion (p = 0.02) only in the plasma because the cerebrospinal fluid values were higher during the day.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Clinical trials: specific problems associated with the use of a placebo-control group.

In order to test hypotheses prospectively with hard data and against placebo, the scientific method of clinical trials has been developed. The present paper focuses on specific problems associated with the use of a placebo control group. (a) The placebo highlights the ethical dilemma that a controlled clinical trial can place us in. (b) Also, in a trial an atmosphere is created of enhanced risks of placebo effects. (c) "Significantly different from placebo" does not necessarily mean clinically relevant. (d) A biased placebo period due to carry-over effect is a common problem of controlled trials with a cross-over or self-controlled design. (e) Likewise an asymmetric placebo group is also a common problem in parallel-group designs. (f) The response to a placebo is generally small in comparison with the response to active treatment and is therefore sometimes more susceptible to bias. It is emphasized that routinely accounting for such problems may further improve the powerful method of controlled clinical trials.

Controlled Clinical Trials as Topic↗
PubMed1992

[Lipid indicators of vascular risk. A cross-sectional study of a group of coronary patients, a group of subjects with normal coronary angiography and a control group].

During a transverse survey, 3 groups of men with the same weight and age were compared. Group I included 42 patients with coronary disease documented by coronarography, group 2 included 19 subjects with normal coronary angiograms, and group 3 included 27 healthy controls who had not undergone coronarography. Subjects presenting diabetes or any factor associated with secondary dyslipidemia or able to modify lipid levels were excluded from study. The following parameters were measured: total cholesterol (Chol), triglycerides (TG), HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C), apoprotein A1 (apoA1), apoprotein B (apoB), lipoprotein (a) or Lp(a), fibrinogen, insulinemia and plasminogen activator inhibitor activity (PAI). The levels of chol, LDL-C and ApoB were the same in the 3 groups. The levels of TG, HDL-C, apoA1 and the ApoA-1/APoB ratio were significantly different between groups 1 and 2, on the one hand, and groups 1 and 3, on the other hand. The levels of Lp(a) and insulin were similar in the 3 groups. Fibrinogen levels were slightly higher in group 1 than in group 3. There was no significant difference between groups 1 and 2 with regard to any of the parameters. Subjects with angiographically normal coronary arteries and subjects with documented coronary disease exhibited similar lipid abnormalities. In this study, TG, HDL-chol, apoA1 and the apoB ratio were better predictors of cardiovascular risk than Chol, LDL-C or apoB.

Adult↗
PubMed2006

Minimization method for balancing continuous prognostic variables between treatment and control groups using Kullback-Leibler divergence.

This paper proposes a method for balancing prognostic variables between treatment and control groups in design of clinical trials. It assumes that some of prognostic variables are continuous and others are categorical and that they are independently distributed. The proposed method uses the Kullback-Leibler divergence (KLD) as the index of difference in distribution between two groups. It sequentially allocates each subject to a group using a biased coin method so as to reduce the estimate of KLD. That is, when first i subjects have been allocated to two groups and the (i+1)th subject is enrolled, the KLD is estimated if the (i+1)th subject was to be allocated to either of the groups, and the subject is then allocated with a certain probability, e.g. 0.80, so as to make the KLD small. Simulation studies based on the hypothetical prognostic variables and on the actual data of hyperlipidemia patients were carried out in order to compare the proposed method with the Pocock-Simon method, which transforms the continuous prognostic variables into categorical variables by dividing the whole scale into several categories. The p values of homogeneity test of means and variances were used to evaluate the achieved balance. The observed p values in the proposed method were better than those in the Pocock-Simon method. In addition to the balance, the precision of parameter estimates assuming analysis of covariance model was examined. The results showed the precision of estimators tended to be more stable in the proposed method than the Pocock-Simon method.

Clinical Trials as Topic↗
PubMed1993

Spinal sagittal mobility and joint laxity in young ballet dancers. A comparative study between first-year students at the Swedish Ballet School and a control group.

The present study compares spinal configuration, spinal range of motion and joint mobility in first-year students of the Swedish Ballet School and in nondancing students of corresponding age and sex in a state school. The study comprises all the first-year (fourth grade) students (n = 23) at the Swedish Ballet School: 11 boys and 12 girls. Their dance practice time was 10 h per week. Thirty-six children in the fourth grade at a state school comprised the control group. None of the controls took ballet classes or participated in organised gymnastics out of school. The neutral spine configuration in standing and the sagittal spine mobility were measured using Debrunner's kyphometer and Myrin's inclinometer. Joint laxity was measured by employing a modified form of the Contompasis method. Compared with the controls, the dancers showed a higher incidence of joint hypermobility, greater mobility of the thoracic spine, a less prominent lordosis of the lumbar spine and a less prominent kyphosis in the thoracic spine in the neutral standing position. The dancers had done little or no ballet training before entering the ballet school at the age of ten. The results agree with those of earlier studies and suggest that increased flexibility is an asset for those being selected as future ballet dancers.

Child↗
PubMed1993

Control group studies of suicide survivors: a review and critique.

Empirical studies of suicide survivors with designs that include control groups are reviewed. Investigations are discussed individually with respect to those in which participating survivors are friends or a combination of many different relationships to the deceased, parents of the deceased child, and spouses. Following the review is a brief discussion of the commonalities of the findings and the most frequent methodological difficulties. Concluding comments suggest methodological improvements as well as issues and groups for which additional investigations are needed.

Accidents↗
PubMed1987

Confounding in epidemiologic studies: the adequacy of the control group as a measure of confounding.

A model for confounding in epidemiologic studies is developed based on the adequacy of the "control" group, instead of the widely used criterion of collapsibility, as a measure of confounding. It is shown that conditions for no confounding in both cohort and case-control studies derived under this model generally agree with the conditions for confounding derived inductively by Miettinen and Cook (1981, American Journal of Epidemiology 114, 593-603). The concept of confounding on which this model is based is compared with the collapsibility criterion in terms of its utility in the design and analysis of epidemiologic studies.

Biometry↗
PubMed2004

High prevalence of personality disorders among healthy volunteers for research: implications for control group bias.

Individuals who volunteer as control subjects for clinical studies are regularly screened for Axis I diagnoses, but seldom screened for Axis II disorders. This study examined the relative rates of Axis II diagnoses among 341 volunteers passing an initial telephone screen for entry into biological research studies. Axis I and II diagnoses by DSM-IV were assigned by best estimate after structured clinical interview, and subjects were categorized into one of three groups based on their diagnostic profiles: (1) volunteers without lifetime Axis I or II diagnoses ("healthy controls"), (2) personality-disordered volunteers without any history of Axis I pathology, and (3) personality-disordered volunteers with past (but not current) Axis I pathology. The results revealed a high prevalence of personality disorders (44.4%) among these volunteers. Several clinically relevant self-report inventories were used to demonstrate important characterological differences between the three comparison groups. Although inventory results demonstrated multiple differences between all three groups, most scales revealed differences between healthy controls and the two personality-disordered groups (with or without lifetime Axis I diagnoses), suggesting that most of the variance was accounted for by the presence or absence of an Axis II disorder, not a past Axis I disorder. These results suggest that personality-disordered volunteers may bias a control group due to the infrequent screening for Axis II disorders among volunteers for medical and psychiatric research. Implications are discussed for routine Axis II screening of volunteers for research with specific diagnostic instruments.

Adult↗
PubMed2006

WMS-III Logical Memory performance after a two-week delay in temporal lobe epilepsy and control groups.

Conventional memory assessment may fail to identify memory dysfunction that is characterized by intact recall for a relatively brief period but rapid forgetting thereafter. This study assessed immediate memory and retention after 30-minute and two-week delays in a control group (n = 25) and a group of individuals with temporal lobe epilepsy (TLE, n = 25). For raw free recall, thematic unit, and recognition memory scores from the Wechsler Memory Scale-3rd ed. (WMS-III) Logical Memory (LM) subtest, there were no group x trial interactions and the TLE group performed significantly worse than the controls on all trials. At the individual level, none of the patients (0%) demonstrated isolated free recall impairment at the two-week delay when raw scores were analyzed, and one patient (4%) but also five controls (20%) did so when percent retention scores were examined. In summary, TLE patients did not demonstrate disproportionate forgetting over two weeks on a widely used story memory test.

Adult↗
PubMedDate not supplied

Posttraumatic headache: biopsychosocial comparisons with multiple control groups.

OBJECTIVE: This study examined somatic, psychological, and cognitive functioning of subjects with posttraumatic headache in comparison with multiple control groups. BACKGROUND: Posttraumatic headache is not as widely studied as other forms of headache (eg, tension-type, migraine). Previous research has suggested poor psychological functioning in patients with posttraumatic headache in comparison with other groups of patients with pain; however, this group has yet to be compared with a group of persons who have experienced trauma but are headache-free. DESIGN AND METHODS: Nineteen subjects with posttraumatic headache were studied, with full assessments available for 14 participants. Comparison groups, containing 16 participants each, included another headache group, a nonheadache group, and a trauma (motor vehicle accident) survivor nonheadache group. Participants completed several measures assessing somatic, psychological, and cognitive functioning. RESULTS: Findings revealed that the posttraumatic headache group exhibited significantly poorer functioning than the comparison groups on several measures including the Psychosomatic Symptom Checklist, Postconcussion Syndrome Checklist, axis II psychiatric diagnoses, Minnesota Multiphasic Personality Inventory, and the Daily Hassles Scale (frequency and total). Additionally, they scored higher on the following: number of axis I psychiatric diagnoses, the Daily Hassles Scale (intensity), Beck Depression Inventory, State-Trait Anxiety Inventory, and State-Trait Anger Expression Inventory. The posttraumatic headache group was similar to the other trauma group on the Posttraumatic Stress Disorder Symptom Checklist and the Life-Trauma Checklist. CONCLUSIONS: This study confirmed the distress seen in this understudied population of persons with headache and highlights areas of focus for proper assessment and treatment of those with headache and who have had an accident.

Accidents, Traffic↗
PubMed1978

[Method of medical history taking and control group recruitment in oncoepidemiological studies].

Some methodical aspects of using the questionnaire as one of the basic tests, employed in oncoepidemiological investigations, are analysed. Under discussion is the potentialities and limits of the questionnairing method; the rules and ways of the optimum application of the given test to obtain the most comprehensive and objective enough information are reported. Also, the principles and criteria of selecting control groups in oncoepidemiological investigations are considered. The factors and conditions which may cause significant differences between the control and "test" groups irrespective of the genesis of the affection under study are discussed. An analysis is made of a number of typical methodical errors in oncoepidemiological investigations.

Clinical Trials as Topic↗
PubMed2004

Selenium levels of patients with newly diagnosed prostate cancer compared with control group.

OBJECTIVES: To compare the toenail selenium level of patients with prostate cancer with that of controls. A tumor-protective effect of selenium has been discussed for many years. Published data about the influence of the selenium level in the plasma and toenails are controversial. METHODS: Our prospective study included 150 patients. Of these, 70 patients had recently diagnosed prostate cancer (cancer group) and 80 patients had no evidence of prostate cancer (negative digital rectal examination and prostate-specific antigen level within age-specific range or negative biopsies) or any other malignant disease (control group). Toenail clippings exhibit selenium levels for up to 1 year. Both groups were compared by assessing their selenium levels using inductively coupled plasma dynamic reaction cell mass spectrometry after microwave-assisted closed vessel digestion. The results of the selenium levels in both groups were statistically compared using the Wilcoxon test. Possible correlations between the selenium level and age, body mass index, smoking habits, and prostate cancer were analyzed by multiple regression analysis. RESULTS: The median age of the cancer and control group was 65 and 69 years, respectively. The median toenail selenium level in the cancer and control group was 528 ng/g (range 393 to 4274) and 502 ng/g (range 201 to 831), respectively (P value not statistically significant). Furthermore, no correlation was found between selenium level and age, body mass index, or smoking status. CONCLUSIONS: The patients in our study with newly diagnosed and not yet treated prostate cancer did not have different toenail selenium levels than controls. Body selenium levels may not influence prostate cancer incidence. A protective effect of selenium for prostate cancer seems questionable.

Aged↗
PubMed1997

Selecting a control group in studies of the familial coaggregation of two disorders: a quantitative genetics perspective.

We sought to compare four different definitions of control groups in studies of the coaggregation between two disorders (A and B) on: 1) their ability to detect valid familial coaggregation; 2) their liability to artifactual evidence for familial coaggregation; and 3) their robustness to the overselection of comorbid cases. Using a quantitative genetic model of transmission, we simulated sibling pairs with familial and nonfamilial sources of comorbidity. Four different definitions of controls were tested to predict disorder B in siblings of cases vs. controls: 1) unscreened controls included subjects with A or B as well as subjects with either A or B; 2) in the symmetrical selection method, controls included only subjects without A; 3) supernormal controls included only subjects without A or B; and 4) in the pure proband method, cases included subjects with A only, and controls included only subjects without A or B. In the absence of selection bias, 1) the unscreened control and the symmetrical selection methods did not yield spurious evidence for familial coaggregation and could detect familial coaggregation; 2) the supernormal controls yielded spurious evidence of familial coaggregation; and 3) the pure proband method sometimes yielded spurious evidence for negative familial coaggregation, and had limited power to detect familial coaggregation. However, the pure proband method was the only one unaffected by overselection of comorbid cases. In the absence of selection bias, both the unscreened control and the symmetrical selection methods are appropriate, and the robustness of the pure proband method to overselection of comorbid cases may be an interesting feature in studies using clinical samples. Moreover, quantitative genetics methods may offer important advantages in the study of familial coaggregation.

Anxiety Disorders↗