The 7 Minute Screen (7MS: Solomon et al., 1998)

The Seven-Minute Screen Neurocognitive battery is a brief screening test for cognitive impairment aimed at early identification of dementia (Solomon et al., 1998). It consists of four tests (temporal orientation, short- and long-term memory, naming, visuospatial organisation, semantic processing and storage), selected because they examine cognitive domains typically impaired in Alzheimer’s disease (see pages A9-A12). Abnormalities in these domains are considered highly sensitive in identifying early stage Alzheimer’s disease (Solomon et al., 1998). The 7MS has excellent predictive validity and can reliably distinguish Alzheimer’s disease from normal ageing and other dementias, such as fronto-temporal dementia (e.g.,

Drake et al., 2003; Meulen et al., 2004).

Solomon et al. (1998) validated the test in a community sample of 60 patients with Alzheimer’s disease and 30 healthy controls. He reported an overall test/retest reliability in the range of 0.83 to 0.92 and an inter-rater reliability of 0.93. The 7MS classified 92% of patients with Alzheimer’s disease correctly and 96% of control subjects correctly. Unlike the MMSE, scores on the 7MS are not influenced by age, sex or education.

The 7MS has been widely accepted as a screening test for identifying early Alzheimer’s disease due to its good diagnostic power and reliability (e.g., Del Ser et al., 2006; Drake et al., 2003; Meulen et al., 2004; Skjerve et al., 2007; Tsolaki et al., 2002). Meulen et al. (2004) reported a high level of sensitivity of 92.9% for Alzheimer’s disease and 89.4% for other types of dementias, and equally high specificity in both populations (93.5%).

However, in Meulen’s et al. (2004) study, performance was influenced by age, sex and education.

Compared to the MMSE, Meulen et al. (2004) reported the 7MS is more sensitive in identifying Alzheimer’s disease. Others have indicated the 7MS is a useful brief screening tool for deciding who would benefit from further neuropsychological assessment (Henderson, 2004; Solomon et al., 1998).

6.5.1.1 7MS subscales

The 7MS consists of the following 4 subscales:

1. Benton Temporal Orientation (BTO): In this test, orientation to time is measured and quantified by the degree of error. The subject is asked the

date (day-month-year) and time. The fewer errors made, the more likely the full score is given. For example, 10 points are subtracted for each year off the target year, 5 points for each month off the target month, 1 point for each date and day of the week off the target date and day, and 1 point for each 30 minutes off the correct time. However, when a question is met with a non-response or a response of “I don’t know”, the subject is asked to guess. If they refuse to guess, no points are deducted. The maximum total error score is 113, which indicates the worst possible performance. The best score is 0. For the purpose of analysis, only errors are recorded as high scores indicate poor performance.

2. Memory (Enhanced cued recall: ECR): Enhanced cued recall is a memory test that induces semantic processing and encoding, and is sensitive to early Alzheimer’s disease (Grober et al., 1988). Patients with Alzheimer’s disease are typically unable to benefit from semantic cues to facilitate remembering.

This test consists of 16 pictures, which are presented four at a time on four individual cards. During the learning trial of each pictured item, the subject is given a semantic cue to assist with learning the to-be-remembered item.

For example, “There’s an insect on this page; what is it?” Immediately after presentation of all items, the subject is asked to free recall as many of the pictures as possible. After a short interval, during which a distracter task is presented, the subject is asked to free recall all pictures. The appropriate semantic cue is provided for unnamed pictures. For example, “I showed you a picture of a musical instrument; what was it?” Scores range between 16 (maximum) and zero.

3. Clock Drawing (CD): Clock Drawing measures visuo-spatial memory and visuo-constructional ability, which are usually impaired in mild and moderate Alzheimer’s disease (Brodaty and Moore, 1997; Esteban-Santillan et al., 1998). In this test, the subject is asked to draw the face of a clock and place the hands at a fixed time “twenty-to-four”. Points are deducted for different types of errors. These include missing numbers, incorrect order and position of numbers. Points are also deducted if both hands are not present, the hour or minute number is not indicated and if the hands are proportionally incorrect. The best score is 7, which is the maximum total score; the lowest is zero.

4. Category fluency (CF): Category fluency measures the integrity and ability to access semantic memory and is a sensitive marker of Alzheimer’s disease (Monsch et al., 1992). In this test, the subject is asked to generate as many words as possible from the semantic category animals and is given a 60-second time limit. The total number of animals named is the score recorded.

The best score is 45. If no animals are named, a score of zero is assigned.

6.5.1.2 Calculating the 7MS total score

To determine the degree to which the 7MS discriminated between control subjects and patients with Alzheimer’s disease, Solomon et al. (1998) estimated a logistic regression model using the raw scores of the four subtests as predictor variables:

Ln [P/(1-P)] = 35.59 – 1.303*ECR – 1.378 * CF + 3.298 * BTO - 0.838 * CD

P indicates the probability of having Alzheimer’s disease, and ECR, VF, BTO, and CD are the scores for the Enhanced Cued Recall, Category Fluency, Benton Temporal Orientation, and Clock Drawing tests, respectively. The natural logarithm (Ln) of P/(1-P) is equal to the total 7MS score of the above logistic regression formula. The probability of having dementia decreases with a lower total score. For example if the total score is -24.6, the probability of having dementia is less than 1%. If the total score is 0, the probability of dementia is 50%. Finally, when the total score is more than 7 the risk is more than 99.9% (Solomon et al., 1998).

In Solomon et al’s. (1998) initial study, total scores from the 7MS that fell between the normal control threshold (probabilities less than 0.3) and dementia (p>0.7) were not categorised (diagnosis deferred) and it was recommended to re-test these subjects 3-6 months later. This indicated that the subject’s performance did not fit neatly into either category.