http://spssx-discussion.165.s1.nabble.com/ANOVA-Assumption-of-Independence-tp5719551p5719567.html
I would state your assumption of independence in a different way.
What is assumed for the sake of testing is that the errors are
independent. That is seldom achieved perfectly. What we do
insist on is that the major "sources of variance" be accounted for --
by including factors or covariates in the design.
You describe a Student-by-Success design, where Success would be
a within-student effect. If, as seems likely, the same teachers appear
more than once, then there would be a Teacher effect to be taken into
account. If there aren't a large number of teachers, you hardly have
data to generalize across "Teachers" as a between-Teacher effect, to
compare "older" versus "younger" (or by experience) .
If there are a lot of years of data, then it is possible that there also
could be a Year-of-test effect. (For instance, in the US: It is known
that the scoring on SAT college-entrance tests vary a bit by year to year,
and they did somewhat dramatically change their standardization at a
specific year in the past. Recently, high scores are easier to get.)
- I can imagine, for a huge amount of historical data, that one could
examine "Success" as a within-Teacher effect, to see whether it changes
systematically with Years-of-Experience. If there is anything there, I
think I would expect it to be some improvement in the first few years.
I expect competition between experience and enthusiasm
--
Rich Ulrich
Date: Fri, 19 Apr 2013 09:13:34 +0100
From:
[hidden email]Subject: ANOVA Assumption of Independence
To:
[hidden email]
Hi,
Not strictly a SPSS question but a stats
question instead, hoping it may take interest to others and elicit a response from
any one of the list members.
Suppose I have multiple records per student, for
simplicity say 3 records per student, each record representing each of their A-Levels
undertaken in secondary school. Suppose each A-Level is taught by a single
teacher and data is collected on the age of the teacher (or years of experience
of teacher – essentially an interval measure) and also a dichotomous variable indicating
pass or failure of the A-level.
Would it be valid to use an ANOVA to test if
the mean age (or years of experience of teacher) is different between the 2
groups (Pass vs. Failure).
One of three assumptions of ANOVA is that the
groups must be independent. What I describe above instinctively feels like this assumption is
violated. So if ANOVA cannot be used, how should I be analyzing this data to
answer this same questions?
Many thanks in advance.
Jignesh