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The three main questions to ask yourself about any report before applying its findings to your patients are:

1) Are the results valid?
2) What are the results?
3) Will the patients help me with my individual patient?

The data required to answer these questions varies between the domains and, depending upon the type of question, the types of evidence used.

Are the results valid?

To the extent that a screening test is used to identify the presence or absence of a disease, many of the measures of validity are the same as those for diagnosis .

You will also want to know if there is randomized trial evidence that earlier intervention works?  This calls for a fairly complex trial since the researchers will first have to randomized patients to those that are screened and those that are not screened.  Then the patients that produce positive results will have to be randomized for treatment and non-treatment.  As screening is performed on an asymptomatic population, the patients that were not screened may not develop the disease and may skew the results.

What are the results?

More often than not, screening studies don't produce results so much as recommendations.  You will have to determine whether the recommendations are valid.  In support of the recommendations, researchers will often produce such statistics as Relative Risk Reduction, Absolute Risk Reduction, Number Needed to Treat, or even Number Needed to Screen.  These statistics are treated in greater depth in the Important Concepts section on screening.

Will the results help me in patient care?

To determine whether to follow the results of a screening study, you will need to determine three things:

1) What are the benefits?
        Is there, in fact, a treatment for this condition?
        Can early detection assist in preventing the condition from occurring?
        Does early detection of untreatable conditions assist in quality of life decisions?

2) What are the harms?
        Does the treatment produce side effects?
        Are there adverse effects of the screening?
        Will there be unnecessary treatment due to false positive results?
        Will there be anxiety generated by the investigations?
        What are the costs and inconveniences incurred during investigations and treatment?
        Is the test sensitive enough to prevent false reassurances for those who actually have the condition?

3) How do the benefits and harms compare in different people and with different screening strategies?
        Does screening affect people differently at different ages?  races? genders?
        Is the risk of disease the same for all people?

More often than not, reports on screening take the form of clinical practice guidelines.  Like systematic reviews, these reports carry special concerns of their own.

BIAS: Were the data identified, selected and combined in an unbiased fashion?  Were the criteria for selection and exclusion of data clear?  Did the researchers include data that did not support their theory?

VALIDITY:  Were all important options and outcomes specified?  Were important recent developments included?  Has the guideline had peer review and testing?

RECOMMENDATIONS;  How strong are the recommendations.  Could the uncertainty in the evidence change the guideline's recommendations?   Are the recommendations applicable to my patients?

The University of Alberta provides a worksheet on analyzing practice guidelines.

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