Tuesday, June 9, 2009

Semantic differential scale.

What is a semantic differential scale ? Explain the steps in construction of the scale. When will you use this scale ?

THE SEMANTIC DIFFERENTIAL SCALE

The terms semantic differential scale refers to any collection of rating scales anchored by bipolar adjectives. It is very flexible approach to obtaining measures of attitudes. The object that is rated is called the “concept” and almost anything can be rated including family planning, cosmetics, shrikhand, political parties, etc.

Normally, a semantic differential scale is based on a seven-point rating scale for each of a number of attributes relating to the research topic. The extreme points represent the bipolar adjectives with the central category representing neutral. In the semantic differential scale only the extremes have names. The in-between categories have either blank spaces or sometimes a number. Some examples of the scale are as follows:
Good ………………………………. Bad
Honest………………………………. Dishonest
Progressive………………………….. Behind the times

The preparation of a semantic differential scale for a study requires expressing the things that could be used to describe the object, and thus serve as a basis for attitude formation, it terms of positive and negative statements. The negative phrase is sometimes put on the left side of the scale and sometimes on the right. This prevents a respondent with a positive attitude from simply checking either the left or right hand sides without reading the describing words.

The scale can be used for a variety of purposes. It can be used to check whether a respondent has a favorable attitude towards the object, which out of three neighborhood banks has the mot appealing profile for housewives. Etc.

It is possible to assign points to individual cells in the scale. Then one could arrive at the scores for comparisons of different objects. The figure1 gives an example based on image study of three neighborhood banks among a sample of 100 housewives.

SUMMATIVE MODELS: THE LIKERT SCALE
The summative models assume that the individual items in the scale are monotonically related to the underlying attributes and a summation of the item scores is related linearly to the attitude. In a summative model, one obtains the total score by adding scores on individual items. For the statements that imply negative attitudes, the scoring is reversed. The scales allow an expression of the intensity of feeling. These scales are also called Likert scales. Here, instead of having just “agree” and “disagree” in the scale, we can have intensities varying from “strongly agree” to “strongly disagree”.

The scale construction consists of the following steps:

1) Write a large number of statements that concern the particular attitudinal object being investigated. For instance one may be looking at the role of voluntary agencies in providing health services in rural areas. Most of these statements should either be moderately positive or moderately negative. Natural items are generally avoided in these scales. The items should be evenly divided between positive and negative statements.
2) Administer the poll of statements on a group of respondents who are similar to the population on whom the scale will be used. For example, if we want to study the attitude of housewives the pool should be administered on a group of housewives with similar background to our final population.
3) Assign scale values to the degrees of agreement or disagreement with each item. The particular values may differ from one researcher to another. Sometimes one may adopt the values 1, 2, 3, 4, 5 and sometimes +2, +1, 0, -1, -2. For negative items the directions should be reversed.
4) Calculate a total attitude score for each respondent using the same scaling procedure. The distribution of total scores is then used to refine the list of items. This step is called item analysis.
5) Items analysis : Analyze the responses and select for the scale those items which most clearly differentiate between the highest and lowest scores. This can be done by dividing the respondents into the high and the low scoring categories. The high scorers can be assumed to be with favorable attitudes and the low scorers can be taken as having the least favorable attitudes. If the statement is a good one, then it is a safe to expect that the mean score for the favorable group would be greater than the mean score for the unfavorable group. If the mean scores across the two groups, for an item, are found nearly equal or equal, then that statement can be dropped from the scale. One can take the high group as the twenty-five per cent of all total scores and the low group as the lowest twenty-five per cent. Alternatively we divide the respondents into quartiles and compute the median score for each item for the highest twenty-five per cent and the lowest twenty-five per cent of scale scores.
6) The statements remaining in the pruned list are randomly ordered on the scale form. The positive and negative ones are mixed.
7) The scale is now administered on the respondents who are asked to indicate their degree of agreement with the item. A respondent’s score is generated as the sum of his scores on each statement.
The summated scales have certain advantages. They are easy to construct, are highly reliable and can be adapted to the measurement of many different kinds of attitudes.

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