Labor force
All civilians who are working or actively looking for work, plus members of
the Armed Forced stationed in the U.S.


Labor force participation rates
The ratio of the population working or looking for work in an age-sex category
to the total population in the category.


Laboratory experiments
Experiments conducted in a controlled setting.


Laddering
A probing technique, used in one-on-ones and focus groups, designed to delve
into the real reasons for participants' attitudes and behaviour toward the topic.
It is generally considered to be an intensive technique. The moderator seeks the
reason behind each answer until he or she arrives at a basic human need such
as ego or status.


Lelly triads
Also known as repertory grids. used especially by advertising agencies to elicit
consumer language for the products in question.  Products (or whatever) are
written or pictured on cards which are dealt three at a time. The respondent is
invited to pick the odd one out and explain why it is odd. The language and
key discriminators are noted.


Level of significance
Probability of making a Type I error.


Lifestyle research
Research that attempts to explain behaviour by analysing people's attitudes,
hobbies, activities and opinions. Often associated with psychographic research.


Lifestyle selectivity
Selectivity based on lifestyle habits of segments of the population, e.g.,
hobbies, interests, ownership etc.


Likert scale
A scale in which the respondent specifies a level of agreement or disagreement
with statements that express a favourable or unfavourable attitude toward the
concept under study. See also semantic differential.


Listed sample
A sample which contains only directory-listed telephone households.


Listed telephone households
Households which are listed in published telephone directories.


Logit model
A version of regression analysis using an S-shaped curve instead of a straight
line. Used when responses are binary, e.g., yes/no, rather than continuous
numbers.


Long census form
The decennial census questionnaire that was answered by a sample of the
population. Data from the long form are available only for large geographic
areas because the Census Bureau protects the anonymity of all respondents.


Longitudinal study
A long-term survey based on repeated analysis of either the same sample
(called a panel study) or new samples chosen at regular intervals.