Alternatively generic himcolin 30 gm otc impotence mayo, the group can be omitted from the analyses although this will reduce the generalizability of the results himcolin 30gm low cost erectile dysfunction effects on women. As a rule of thumb order himcolin 30 gm online erectile dysfunction treatment by exercise, the maximum number of cells that can be tested using chi-square is the sample size divided by 10 cheap 30gm himcolin free shipping 60784 impotence of organic origin. Thus, a sample size of 160 could theoretically support 16 cells such as an 8 × 2table,a5× 3tableora4× 4 table. However, this relies on an even distribution of cases over the cells, which rarely occurs. In practice, the maximum number of cells is usually the sample size divided by 20. In this data set, this would be 141/20 or approximately seven cells which would support a 2 × 2or2× 3table. The pathway for analyzing categorical variables when some cells have small numbers is shown in Figure 8. However, if two or more unrelated groups need to be combined, they could be described with a generic label such as ‘other’ if neither group is more closely related to one of the other groups in the analysis. To ensure that all output is self-documented, it is important to label each new variable in Variable View after re-coding and to verify the frequencies of place3 using the commands shown in Box 1. Non-ordered Cells with small Exact methods categories numbers Categorical Combine data cells Each cell has Pearson’s or sufficient continuity corrected numbers chi-square Combine cells Non-parametric Ordered with small statistics or chi-square categories numbers trend Figure 8. Rates and proportions 265 Frequencies Place of Birth (Binary) Valid Cumulative Frequency Per cent per cent per cent Valid Local 90 63. With the small cells combined into larger cells, the footnote shows that no cell has an expected count less than ﬁve and thus the assumptions for chi-square are met. Crosstabs Place of Birth (Binary) * Prematurity Crosstabulation Prematurity Premature Term Total Place of birth Local Count (binary) % within place of birth 29 32. In addition, the odds ratio (as discussed in Chapter 9) can also be reported for 2 × 2 tables to indicate the size of the association between the two variables. In the example above, the results can be presented as ‘Of the 132 babies, 29 of the 90 babies who were born locally were premature (32. A chi-square test indicated that there was no signiﬁcant association between prematurity and place of birth (P = 0. When presenting crosstabulated information of the effects of explanatory factors for a report, journal article or presentation, it is usual to present the results in tables with the outcome variable presented in the columns and the risk factors or explanatory variables presented in the rows as shown in Table 8. The chi-square analyses show that the number of males and females referred for surgery is signiﬁcantly different but that the per cent of premature babies from regional or overseas areas is not signiﬁcantly different from the per cent of premature babies in the group born locally. A 95% conﬁdence inter- val around this difference is valuable in interpreting the signiﬁcance of the difference Rates and proportions 267 Table 8. The difference in proportions is calculated as p1 − p2 and the standard error √ of the difference as ((p1 ×(1 − p1)∕n1)+(p2 ×(1 − p2)∕n2)),wherep1 is the proportion and n1 is the number of cases in one group and p2 is the proportion and n2 is the number of cases in the other group. This type of presentation is useful, for example, when comparing percentages between two groups that were studied in different time periods and the outcome of interest is the change over time. The 95% conﬁdence interval for the difference between genders does not contain the zero value of no difference as expected because the P value is signiﬁcant. On the other hand, the conﬁdence interval for the difference between places of birth contains the zero value indicating there is little difference between groups and that the P value is not signiﬁcant. Research question Question: Are babies who are born prematurely more likely to require different types of surgical procedures than term babies? Null hypothesis: That the proportion of babies who require each type of surgical procedure in the group born prematurely is the same as in the group of term babies. Variables: Outcome variable = procedure performed (categorical, three levels) Explanatory variable = prematurity (categorical, two levels) In situations such as this where the table is 3 × 2 because the outcome has three lev- els, both the row and column cell percentages can be used to provide useful summary statistics for between-group comparisons. In addition, the column percentages can be obtained by clicking on Cells in the Crosstabs dialog box and ticking Column under Percentages. Crosstabs Prematurity * Procedure Performed Crosstabulation Procedure performed Abdominal Cardiac Other Total Prematurity Premature Count 9 23 13 45 % within prematurity 20. Rates and proportions 269 The row percentages in the Crosstabulation table show that fewer of the premature babies required abdominal procedures than the term babies (20. In addition, more of the premature babies than the term babies had other pro- cedures (28. Since the contingency table is now larger than 2 × 2, the Fisher’s exact test is not produced and the Pearson’s chi-square test is used. However, this P value does not indicate the speciﬁc between-group comparisons that are signiﬁcantly different from one another. In practice, the P value indicates that there is a signiﬁ- cant difference in percentages within the table but does not indicate which groups are signiﬁcantly different from one another. In this situation where there is no ordered explanatory variable, the linear by linear association has no interpretation. The column percentages shown in the Crosstabulation table can be used to interpret the 2 × 2 comparisons. These percentages show that rates of surgery types in premature babies are abdominal vs cardiac surgery 17. To obtain P values for these comparisons, the Data → Select Cases → If condition is satisﬁed option can be used to select two groups at a time and compute three separate 2 × 2 tables. The original P value from the 2 × 3 table was signiﬁcant because the rate of prematurity was signiﬁcantly lower in the abdominal surgery group compared to both the cardiac and other surgery groups. However, there was no signiﬁcant difference between the car- diac vs other surgery group. This process of making multiple comparisons increases the chance of a type I error, that is, ﬁnding a signiﬁcant difference when one does not exist. A preferable method is to compute conﬁdence intervals as shown in the Excel spread- sheet in Table 8. The rates and their conﬁdence intervals can then be plotted using SigmaPlot as shown in Box 8. The data sheet has the proportions and conﬁdence interval widths converted into percentages for the premature babies in columns 1 and 2 and for the term babies in columns 3 and 4 as follows: Column 1 Column 2 Column 3 Column 4 17. The per cent of premature babies in the cardiac surgery and other procedure groups are almost identical as described by the P value of 1. Premature Term Other procedures Cardiac Abdominal 0 Per cent (%) of group Figure 8. However, the same assumptions apply and the sample size should be sufﬁcient so that small cells with few expected counts are not created. Research question Question: Do babies who have a cardiac procedure stay in hospital longer than babies who have other procedures? Null hypothesis: That length of stay is not different between children who undergo different procedures. Variables: Outcome variable = length of stay (categorized into quintiles) Explanatory variable = procedure performed (categorical, three levels) In the data set, length of stay is a right skewed continuous variable (see Chapter 2). As an alternative to using rank-based non-parametric tests, it is often useful to divide non-normally distributed variables such as this into categories. The ranges are important for describing the quintile values when reporting the results. The number of cases in some quintiles is unequal because there are some ties in the data. Procedure performed * Length of stay quintiles Crosstabulation Length of stay quintiles ≤19 20–22 23–30 31–44 45+ Total Procedure Abdominal Count 5 8 15 11 9 48 performed % within procedure 10. In the crosstabulation, the procedure performed is entered into the rows as explanatory variable and length of stay quintiles are entered in the columns as the outcome variable. Although some cells have only two or three cases, the Chi-Square Tests footnote shows that no cells have an expected number less than 5, so that the analysis and the P value are valid. If the cardiac and abdominal patients are compared, the abdominal group has fewer babies in the lowest quintile and the cardiac group has slightly fewer babies in the highest quintile. In the group of babies who had other procedures, most babies are either in the lowest or in the highest quintiles of length of stay.
Internal Radiation Dosimetry (c) Composition of the target organ (d) Amount of the radioactivity present in the source (e) Shape of the source organ 5 purchase 30gm himcolin overnight delivery erectile dysfunction protocol scam. Does the mean absorbed dose per cumulated activity buy himcolin 30gm online erectile dysfunction pills side effects, S proven 30gm himcolin erectile dysfunction pump pictures, depend on: (a) Absorbed fraction (b) Target mass (c) Photon energy (d) Photon abundance 6 buy himcolin 30gm impotence gandhi. What is the important parameter that is considered in adjusting the activity to be administered to children compared to adults for a nuclear medicine test? Considering the contribution from other organs negligible, calculate the effective dose. Speciﬁc absorbed fractions for radiation sources uniformly distributed in various organs of a heterogeneous phantom. During the passage through living matter, radiation loses energy by interaction with atoms and molecules of the matter, thereby causing ionization and excitation. Radiation biology is a vast subject, and it is beyond the scope of this book to include the full details of the subject. The following is only a brief outline of radiation biology, highlighting the mechanism of radiation damage, radiosensitivity of tissues, different types of effect on living matter, and risks of cancer and genetic effects from radiation exposure. The Cell The cell is the building unit of living matter and consists of two primary components: the nucleus and the cytoplasm (Fig. All metabolic activities are carried out in the cytoplasm under the guidance of the nucleus. The nucleus contains chromosomes, which have a threadlike structure of two arms connected by a centromere (Fig. Chromosomes are formed of genes, which are the basic units of heredity in the cells of all living species. Two categories of cells—namely, germ cells (repro- ductive cells such as oocytes and spermatozoa) and somatic cells (all other cells)—are based on the number of chromosomes they contain. Whereas germ cells contain n number of individual chromosomes, somatic cells contain 2n number of chromosomes in pairs, where n varies with species of the animal. In humans, n is equal to 23; therefore, there are 23 chromosomes in germ cells and 46 chromosomes in somatic cells. In the cytoplasm of the cell exist four important organelles—ribosomes, endoplasmic reticula, mitochondria, and lysosomes—that carry out the 226 The Cell 227 Fig. Endoplasmic reticula are tubular structures mostly responsible for protein synthesis. Mitochondria are ellipsoidal structures with a central cavity and contain speciﬁc enzymes to oxidize carbohydrate and lipid to produce energy. Lysosomes are small organelles in the cytoplasm that contain enzymes capable of lysing many nutrients and cells. The entire cytoplasm is enclosed within a cell membrane made of lipids and proteins. Its primary function is to selectively prohibit or permit the passage of substances into and out of the cell. The growth of living matter is caused by proliferation of cells by cell divi- sion—a process in which a cell divides into two cells. The cell division of somatic cells is called mitosis and that of germ cells is called meiosis. Both mitosis and meiosis, designated as M, consist of four phases: prophase, metaphase, anaphase, and telophase. Each of these phases involves the rearrangement of the number of chromosomes and represents the pro- gression of cell division (Fig. In prophase, the chromosome thickens in the shape of dumbbell with a constriction at the center, called centromere. The nuclear membrane breaks open, leading to the mixture of cytoplasm and nuclear material, and spin- dles made of ﬁbers are formed extending from one end (pole) of the cell to the other. Next in the metaphase, the chromosomes move to and line up at the central (or equatorial) plane of the cell, and the centromeres divide into two, each attaching to the spindle. The last step of cell division involves the deconvolution of the chromosomes leading to the regenera- tion of the nuclear membrane and nucleoli around both poles. Division of cytoplasm (cytokinesis) sets in, and ultimately two daughter cells are formed. The period between the telophase and the S phase is termed G1, and the period between the S phase and the prophase is termed G2 (Fig. During the G1 and G2 periods, no functional activity related to cell division occurs. The period of the entire cell cycle including the M and S phases varies with the types of cells. The S phase normally is the longest and G1 is the most variable phase in the cell cycle. M is the period of mitosis during which the prophase, metaphase, anaphase, and telophase take place. G1 is the period between the telophase and S, and G2 is the period between S and the prophase. It has a double-helical structure consisting of two strands, which are like the two rails of a ladder (Fig. The two strands are connected to each other by rungs made of four bases: thymine (T), adenine (A), guanine (G), and cytosine (C) (Fig. The rungs of the ladderlike structure are formed by bases connected to each other by the hydrogen band (dashed line) and to the sugar molecule on the strands on both sides. Effects of Radiation 231 cule on the strands on both sides, and are paired to each other by hydro- gen bonds. These four bases are arranged in a very speciﬁc manner to form a speciﬁc gene in every living species and provide the unique characteris- tics to these species. These changes result in so-called mutations, which have adverse effects on the genetic codes. At low-dose exposures, the breaks are single stranded and can be repaired by joining the broken components in the original order. At higher exposures, however, double strand breaks occur and the odds for repair decrease. If the cell is not repaired, it may suffer a minor functional impairment or a major consequence (cell death). However, chromosomes themselves can be cleaved by radiation producing single or double breaks in the arms. These aberrations are categorized as chromatid aberrations and chromosome aberrations. Whether chromosome aberrations are induced by single-strand breaks or double-strand breaks in the structure determines the fate of the cell. In single-strand breaks, the chromosome tends to repair by joining the two fragments in a process called restitution, provided sufﬁcient time is allowed. Random combination of these fragments will then produce acentric and dicentric chromatids as illustrated in Figure 15. Such chromosomes suffer severe consequences due to the mismatch of genetic information. Radiation Biology A G T G T A T C A C A A G T G T B T C A C A A G G T C T C A A G T G T D T C A C A G A G T G T G E C T C A C A C F Fig. Radiation Biology If radiation produces single-strand breaks in two separate chromosomes, then there are four ways of recombining the broken ends as shown in Figure 15. However, these cells suffer severe consequences because of the mismatch of genetic information from two separate damaged chromosomes. The translocation is a process in which two fragments—one with a centromere from one chromosome and one without a centromere from another chromosome—combine to form a new chromosome (Fig.
P. Hamil. University of Alabama, Birmingham.