# jspsych-survey-likert plugin

The survey-likert plugin displays a set of questions with Likert scale responses. The subject responds by selecting a radio button.

## Parameters

Parameters with a default value of *undefined* must be specified. Other parameters can be left unspecified if the default value is acceptable.

Parameter | Type | Default Value | Description
----------|------|---------------|------------
questions | array | *undefined* | An array of objects, each object represents a question that appears on the screen. Each object contains a prompt, labels and required parameter that will be applied to the question. See examples below for further clarification.`prompt`: Type string, default value is *undefined*. The strings are the question that will be associated with a slider. `labels`: Type array, default value is *undefined*. Each array element is an array of strings. The innermost arrays contain a set of labels to display for an individual question. If you want to use blank responses and only label the end points or some subset of the options, just insert a blank string for the unlabeled responses.`required`: Type boolean, default value is false. Makes answering questions required. `name`: Name of the question. Used for storing data. If left undefined then default names (`Q0`, `Q1`, `...`) will be used for the questions.
randomize_question_order | boolean | `false` | If true, the display order of `questions` is randomly determined at the start of the trial. In the data object, `Q0` will still refer to the first question in the array, regardless of where it was presented visually.
preamble | string | empty string | HTML formatted string to display at the top of the page above all the questions.
scale_width | numeric | null | The width of the likert scale in pixels. If left `null`, then the width of the scale will be equal to the width of the widest content on the page.
button_label | string |  'Continue' | Label of the button.

## Data Generated

In addition to the [default data collected by all plugins](overview#data-collected-by-plugins), this plugin collects the following data for each trial.

Name | Type | Value
-----|------|------
responses | JSON string | A string in JSON format containing the response for each question. The encoded object will have a separate variable for the response to each question, with the first question in the trial being recorded in `Q0`, the second in `Q1`, and so on. The responses are recorded as integers, representing the position of the slider on the scale. If the `name` parameter is defined for the question, then the response will use the value of `name` as the key for the response in the `responses` object.
rt | numeric | The response time in milliseconds for the subject to make a response. The time is measured from when the questions first appear on the screen until the subject's response.
question_order | JSON string | A string in JSON format containing an array with the order of questions. For example `[2,0,1]` would indicate that the first question was `trial.questions[2]` (the third item in the `questions` parameter), the second question was `trial.questions[0]`, and the final question was `trial.questions[1]`.

## Examples

#### Basic example

```javascript
var scale_1 = [
  "Strongly Disagree", 
  "Disagree", 
  "Neutral", 
  "Agree", 
  "Strongly Agree"
];

var likert_page = {
  type: 'survey-likert',
  questions: [
    {prompt: "I like vegetables.", labels: scale_1}
  ]
};
```

#### Multiple questions in a random order

```javascript
var scale_1 = [
  "Strongly Disagree", 
  "Disagree", 
  "Neutral", 
  "Agree", 
  "Strongly Agree"
];

var likert_page = {
  type: 'survey-likert',
  questions: [
    {prompt: "I like vegetables.", name: 'Vegetables', labels: scale_1},
    {prompt: "I like fruit.", name: 'Fruit', labels: scale_1},
    {prompt: "I like meat.", name: 'Meat', labels: scale_1},
    {prompt: "I like dairy.", name: 'Dairy', labels: scale_1}
  ],
  randomize_question_order: true
};
```