Arsanilic acid and Rating scale: Difference between pages

Revision as of 22:55, 26 April 2006

Revision as of 02:56, 21 May 2007

Line 1:

A '''rating scale''' is a set of categories designed to elicit information about a [[quantitative]] attribute in social science. Common examples are the [[Likert scale]] and 1-10 rating scales for which a person selects the number which is considered to reflect the perceived quality of a product.

{{Drugbox|

|IUPAC_name = (4-aminophenyl)arsonic acid

| image= Atoxyl.png

| CAS_number= 98-50-0

| ATC_prefix= ?

| ATC_suffix= ?

| PubChem= 7389

| DrugBank= EXPT00575

| chemical_formula = C₆H₈AsNO₃

| molecular_weight = 217.054 g/mol

| bioavailability= ?

| metabolism = ?

| elimination_half-life= ?

| excretion = ?

| pregnancy_category = ?

| legal_status = ?

| routes_of_administration= ?

}}

== Background ==

'''Atoxyl<sup>®</sup >''' (''p-aminophenyl-. arsenic acid'') is the name of a toxic [[arsenic]]-containing ([[arsenical]]) drug used in the late 19th and early 20th centuries.

In [[Psychometrics]], rating scales are often referenced to a statement which expresses an attitude or perception toward something. The most common example of such a rating scale is the Likert scale, in which a person is asked to select a category label from a list indicating the extent of disagreement or agreement with a statement.

==Origins and uses==

The basic feature of any rating scale is that it consists of a number of categories. These are usually assigned integers. For example, an example of the use of a Likert scale is as follows.

Atoxyl was first synthesized in [[1859]] by [[Antoine Béchamp]] by chemically reacting [[aniline]] and [[arsenic acid]]. Béchamp chose the name ''Atoxyl'' referring to the reduced toxicity of the resulting compound, compared to arsenic.

:'''Statement:''' I could not live without my iPod.

Atoxyl was initially used in medicine to treat simple [[skin disease]]s. In [[1905]], two British physicians, H.W. Thomas and A. Breinl, discovered that Atoxyl was active against the trypanosomes of [[sleeping sickness]]. The effect of atoxyl was however not very pronounced, and the necessary [[dosage]] was so high that its [[toxicity|toxic]] side effects far outweighed the benefits. Atoxyl frequently caused [[blindness]] by damaging the [[optic nerve]] and other varied disorders.

:'''Response options:'''

Nevertheless, the discovery of atoxyl's activity against trypanosomes was the basis for a major advance by the bacteriologist [[Paul Ehrlich]]. Ehrlich believed the accepted formula for atoxyl at that time was incorrect. Ehrlich and an organic chemist, Alfred Bertheim, identified the correct structural formula. The correct formula suggested new ways that the atoxyl molecule could be modified, and a series of such derivatives were then synthesized for testing. Testing for anti-[[syphilis|syphilitic]] activity was performed by [[Sahachiro Hata]] who worked in Ehrlich's lab. The result of this team effort was the discovery of the drug [[Salvarsan]] in [[1909]].

:*1. Strongly Disagree

==External links==

:*2. Disagree

:*3. Agree

:*4. Strongly Agree

It is common to treat the numbers obtained from a rating scale directly as measurements by calculating averages, or more generally any [[arithmetic]] operations. Doing so is not however justified. In terms of the [[levels of measurement]] proposed by S.S. Stevens, the data are ordinal categorisations. This means, for example, that to agree strongly with the above statement implies a more favourable perception of iPods than does to agree with the statement. However, the numbers are not interval-level measurements in Stevens' schema, which means that equal differences do not represent equal intervals between the degree to which one values iPods. For example, the difference between strong agreement and agreement is not necessarily the same as the difference between disagreement and agreement. Strictly, even demonstrating that categories are ordinal requires empirical evidence based on patterns of responses (Andrich, 1978).

* [http://www.chemheritage.org/EducationalServices/pharm/chemo/readings/ehrlich/pabio.htm Atoxyl at Chemical Heritage] More about the origins and uses of the medicine.

* [http://stevenlehrer.com/explorers/chapter_7.htm Explorers of the Body] Some info about sleeping sickness and atoxyl.

* [http://preview.pesticideinfo.org/Detail_ChemReg.jsp?Rec_Id=PC37540 Arsonic Acid poisoning information].

* Ihde, Aaron J. ''The Development of Modern Chemistry'', Dover, New York, 1984. pp. 697-698.

More than one rating scale is required to [[measurement|measure]] an attitude or perception due to the requirement for statistical comparisons between the categories in the [[polytomous Rasch model]] for ordered categories (Andrich, 1978). In terms of [[Classical test theory]], more than one question is required to obtain an index of internal reliability such as [[Cronbach's alpha]] (Cronbach, 1951) which is a basic criterion for assessing the effectiveness of a rating scale and, more generally, a psychometric instrument.

[[Category:Aromatic compounds]]

[[Category:Arsenic compounds]]

== Rating scales used online ==

Rating scales are used widely online in an attempt to provide indications of consumer opinions of products. Examples of sites which employ ratings scales are [[IMDb]], [[Epinions.com]], [[Internet Book List]], [[Yahoo! Movies]], [[Amazon.com]], [[BoardGameGeek]], [[TV.com]] and [[Ratings.net]]. The [[Criticker]] website uses a rating scale from 0 to 100 in order to obtain "personalised film recommendations".

In almost all cases, online rating scales only allow one rating per user per product, though there are exceptions such as ''Ratings.net'', which allows users to rate products in relation to several qualities. Most online rating facilities also provide few or no qualitative descriptions of the rating categories, although again there are exceptions such as ''Yahoo! Movies'' which labels each of the categories between F and A+ and BoardGameGeek, which provides explicit descriptions of each category from 1 to 10. Often, only the top and bottom category is described, such as on ''IMDb'''s online rating facility.

With each user rating a product only once, for example in a category from 1 to 10, there is no means for evaluating internal [[reliability (statistics)|reliability]] using an index such as [[Cronbach's alpha]]. It is therefore impossible to evaluate the [[validity]] of the ratings as measures of viewer perceptions. Establishing validity would require establishing both reliability and accuracy (i.e. that the ratings represent what they are supposed to represent).

Another fundamental issue is that online ratings usually involve convenience [[sampling (statistics)|sampling]] much like television polls, i.e., they represent only the conglomeration of those inclined to submit ratings.

Sampling is one factor which can lead to results which have a specific bias or are only relevant to a specific subgroup. To illustrate the importance of such factors, consider an example. Suppose that a film's marketing strategy and reputation is such that 90% of its audience are attracted to the particular kind of film; i.e. it does not appeal to a broad audience. Suppose also that the film is very popular among the audience that does see the film and, in addition, that those who feel most strongly about the film are inclined to rate the film online. This combination may lead to very high ratings of the film which do not generalize beyond the people who actually see the film (or possibly even beyond those who actually rate it).

Qualitative description of categories is an important feature of a rating scale. For example, if only the points 1-10 are given without description, some people may select 10 rarely whereas other may select the category often. If, instead, "10" is described as "near flawless", the category is more likely to mean the same thing to different people. This applies to all categories, not just the extreme points. Even with category descriptions, some may be harsher raters than others. Rater harshness is also a consideration in marking essays in educational contexts. [http://66.102.7.104/search?q=cache:o1l_qRDI9QwJ:www.cambridgeesol.org/rs_notes/rs_nts13.pdf+rater+harshness+references&hl=en&ct=clnk&cd=4].

These issues are also compounded when aggregated statistics such as averages are used for lists and rankings of products. User ratings are at best [[levels of measurement|ordinal]] categorizations. While it is not uncommon to calculate averages or means for such data, doing so cannot be justified because in calculating averages, equal intervals are required to represent the same difference between levels of perceived quality. The key problems with aggregate data based on the kinds of rating scales commonly used online are as follow:

*Averages should not be calculated for data of the kind collected.

*It is usually impossible to evaluate the reliability or validity of user ratings.

*Products are not compared with respect to explicit, let alone common, criteria.

*Only users inclined to submit a rating for a product do so.

*Data are not usually published in a form that permits evaluation of the product ratings.

==References==

* Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. ''Psychometrika, 16'', 297-333.

* Andrich, D. (1978). A rating formulation for ordered response categories. ''Psychometrika'', 43, 357-74.

==See also==

*[[Voting system]]

*[[Rotten Tomatoes]]

*[[Metacritic]]

==External links==

[http://www.rasch-analysis.com/ How to apply Rasch analysis]

[[Category:Aromatic compoundsPsychometrics]]

[[de:Natriumhydrogenarsanilat]]