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Thread: Low Cronbach alpha on recognised instrument

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    Low Cronbach alpha on recognised instrument




    Hi,

    I am using a standard survey instrument that during a meta analysis over 15 years has shown a relability of 0.73 for a particular facet. I conducted cronbach alpha for my study and it came back as 0.51 well below an acceptable level. My question is simple, do I disregard the 0.51 as the instrument has been proven already, or do I remove it from the study and explain due to the 0.51 alpha that I have excluded it from any further correlations etc. Or do I continue to use it, but caution any results against it due to the low alpha number.

    Thanks for any advice in advance.

    Jake

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    Re: Low Cronbach alpha on recognised instrument

    Reliability typically doe not mean Cronbach alpha, so are you saying 0.73 is the reported Cronbach alpha and the instrument's reliability? Please clarify this before we address whether you are even able to compare your value to 0.73 (might be comparing apples to oranges).
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    Re: Low Cronbach alpha on recognised instrument

    The reliability of the OCQ was tested in a meta-analysis by Meyer, Stanley, Herscovitch, & Topolnytsky (2002) with 15 years of OCQ questionnaire results using both the 24 item and 18 item versions of the OCQ. They found the reliability of the OCQ to be .82 for affective commitment, .73 for continuance commitment, and .76 for normative commitment.

    here is the narrative for the instrument.

    I am just wondering if my cronbach alpha comes in below 0.7 what should I do. Use with caution, remove it from study or go with the facts above. Thanks for replying.

    I'm a bit out of my depth here, so any guidance greatly appreciated

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    Re: Low Cronbach alpha on recognised instrument

    I am just wondering if my cronbach alpha comes in below 0.7 what should I do. Use with caution, remove it from study or go with the facts above.
    Who can tell without knowing anything about your study
    (context, theoretical background, objectives, design,
    sampling procedure and sample size, what the scales are
    used for...) ?

    With kind regards

    K.

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    Re: Low Cronbach alpha on recognised instrument

    Are Affective commitment, continuance commitment, and normative committed groupings of instrument questions? If so, are you grouping the same questions for your 0.73. Also DOES the Meyer et. al paper say reliability, cronbach alpha, or uses them interchangeably?
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    Re: Low Cronbach alpha on recognised instrument

    Hi. I'm using SPSS and have grouped the 6 questions of each type (t 18). So cronbach alpha all six AC, then all six NC and then all six CC. Affective came back as .79, Normative as 0.85 but Continuance came back as 0.51. This is an organisational commitment questionaire which I have used in addition to a job satisfaction questionnaire to compare the two and to compare each with demographics if that makes sense. But before I use the information, I elected to run a cronbach alpha as i have seen in other studies/books, but nowhere have I seen what they say you should do if your cronbach comes in below the .7 value. ? So if i am correlating between organisational commitment and job satisfaction should I just use the other two. Is it reasonable/justifiable to remove the continuance aspect based on the low cronbach?
    It is used interchangably and to be honest, I'm new to this so some of it going over my head a bit
    Last edited by JakeMac; 03-12-2013 at 12:53 PM.

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    Re: Low Cronbach alpha on recognised instrument

    A good question is, what are you planning on doing with these data?
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    Re: Low Cronbach alpha on recognised instrument

    Hi JakeMac,

    I apologize if you have done it already, but I have in seen several studies that an unexpectedly low Cronbach's alpha was the result of a data entry/data coding mistake. Have you checked if any specific item of the respective subscale is responsible for dragging down your value?

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    Re: Low Cronbach alpha on recognised instrument

    In the SPSS output there should be a place that says something like Alpha if removed (to go with Regina's comment). If you see this going above the Alpha level this item is suspect. Also be wary of reverse scoring where low is actually high and high is actually low. Many instruments contain reverse scored items that would kill Alpha if you don't enter them in as reverse scored.

    If everything is entered correctly then HlSmith's question really is the key to your answer.
    "If you torture the data long enough it will eventually confess."
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    Re: Low Cronbach alpha on recognised instrument

    Hi all, Thank you all for your time.
    I have reversed score all the negatively worded items. I have also check the item deleted scale which show no significant change to the figure. There is no mssing data etc. I have checked and rechecked this.

    A brief description of what I'm doing
    A demographic survey as independant variable
    A job satisfaction survey as a dependant variable
    A organisational survey as a dependant variable

    From this I want to calculate;
    the mean job satisfaction of the group under different facets scores and a total job satisfaction mean. All these facets has a cronbach of near or over .9,
    the mean organisational commitment of the group which we actuall be a mean for the three different types as opposed to an overal score,
    Correlation between the demographics and the facets of job satisfaction,
    Corelation between the demographics and the 3 types of organisational commitment,
    Correlation between the 3 types of organisational commitment and overall job satisfaction.

    The organisational questionnaire is a 18 question instrument. 6 items for each of the 3 types of commitment. Does that help?

    Thanks again all

    Jake

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    Re: Low Cronbach alpha on recognised instrument

    @Jake I believe that hlsmith's question was more what you plan to do with the info. Is it policy you want to influence or a pilot study. An acceptable alpha is different for these two cases.
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    Re: Low Cronbach alpha on recognised instrument

    It is a cross sectional study for a university dissertation and will not be used for policy but will probably be read by management. I suppose I'm asking if the normal accepted value is .7 then what is the procedure for a research paper that the values comes well below this. If an examiner is to look at what I did and say why did you proceed to use the continuance commitment in the research when it only had a reliabilty cronbach alpha of .51 or am I over analysing this. If I was to declare in the research that due to the fact that the cronbach alpha for this aspect is 0.51 that I have decided to disregard it for the rest of the research. I can do this, but is it a correct train of thought if you were to comment on my decision to do so?

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    Re: Low Cronbach alpha on recognised instrument

    You could use structural equation modelling which takes into account measurement error. For an example see a paper I am a co-author on in Journal of Educational Psychology, vol 105(1) pp.108 where we deal with low reliability of an established measure in this way.

    P.S. see this paper http://link.springer.com/article/10....9101-0?LI=true for the reasons I no longer use alpha.

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    Re: Low Cronbach alpha on recognised instrument

    Very interesting thanks. I have conducted the glb as suggested in your conclusion.
    Here is what I got

    Reliability Statistics
    Lambda
    1 .423
    2 .544
    3 .507
    4 .689
    5 .534
    6 .551
    N of Items 6

    Not sure if that helps though
    I'm far from an expert and may be going further than I need to with this, but learning as I go

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    Re: Low Cronbach alpha on recognised instrument


    I don't think that is the glb. From memory SPSS will not provide the glb. Rather you have to do it in the psych package in R.

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