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Table 1 Study characteristics

From: Air ions and mood outcomes: a review and meta-analysis

Author and year Study objective Study design Blinding Study population Total sample size
Silverman and Kornblueh 1957[27]a,b Evaluate effect of negative and positive ions on the human electroencephalogram and sleep Crossover experiment Not reported 10 healthy adults and 2 additional subjects with chronic stationary neurologic conditions 12
McGurk, 1959[17]c Evaluate effect of negative and positive ions on self-reported feelings of comfort Crossover experiment Single-blind (subjects) 10 college-aged males 10
Yaglou, 1961[19]b Evaluate effect of negative and positive ions on relaxation Crossover experiment Single-blind (subjects) 25 healthy adults (age range: 22–51) 25
Yaglou, 1961[19]b Evaluate effect of negative and positive ions on relaxation and sleepiness Crossover experiment Single-blind (subjects) 6 arthritic patients (age range: 30–62) 6
Assael et al., 1974[11]b Evaluate effect of negative ions on human electroencephalogram Crossover experiment Double-blind 10 healthy participants (age range: 20–65) and 10 subjects receiving tranquilizers 20
Albrechtsen et al., 1978[37]b,c Evaluate effect of negative and positive ions on human well-being and mental performance Crossover experiment Single-blind (subjects) Study 1: six women (age range: 20–30) chosen at random; study 2: 12 subjects (age range: 19–45) selected because they appeared to be most sensitive to ionization Study 1: 6 Study 2: 12
Charry and Hawkinshire, 1981[15]a Evaluate effect of negative and positive ions on mood Crossover experiment Single-blind (subjects) 85 adults (age range: 18–60; mean age: 30) 85
Hawkins, 1981[38]b, c Evaluate effect of negative and positive ions on subjective well-being and comfort Crossover experiment Double-blind Study groups based on three areas of variable air ionization levels within the building (area 1: 20 women; area 2: 32 adults; and area 3: 54 adults) Area 1: 20
Area 2: 22
Area 3: 54
Tom et al., 1981[34]a,b Evaluate effect of negative ions on human performance and mood Randomized controlled trial Double-blind 56 adults (age range: 17–61; mean age: 23) 56
Buckalew and Rizzuto, 1982[12]a,b Evaluate effect of negative ions on subjective feelings of mood and psychological state Randomized controlled trial Double-blind Two groups of 12 paid male volunteers matched on age, education, physical condition, and smoking habits (age range: 20–30; mean age: 22.8) 24
Dantzler et al., 1983[25]a Evaluate effect of positive and negative ions on somatic symptoms and mood changes Crossover experiment Double-blind 9 patients with bronchial asthma (age range: 35–64) 9
Baron et al., 1985[28]a Evaluate effect of negative ions on self-reported affect/mood Crossover experiment Single-blind (subjects) 71 male undergraduate students 71
Deleanu and Stamatiu, 1985[29]a,b,d Evaluate effect of negative ions on psychiatric symptoms Experimental (no control group) Not reported 112 patients with neurasthenias, psychoses, or personality disorders 112
Gianinni et al., 1986[16]a Evaluate effect of negative and positive ions on anxiety, excitement, and suspicion Crossover experiment Double-blind 14 university-affiliated volunteers 14
Gianinni et al., 1986/1987[30]a Evaluate effect of positive ions on anxiety and excitement Crossover experiment Double-blind 12 adult male volunteers 12
Finnegan et al., 1987[40]c Evaluate effect of negative ions on personal comfort rating Crossover experiment Single-blind (subjects) 26 adults working within 5 different rooms of an office building 26
Hedge and Collis, 1987[18]a Evaluate effect of negative ions on mood Crossover experiment Double-blind 28 healthy women (age range: 19–58) 28
Lips et al., 1987[13]b,c Evaluate effect of negative ions on well-being and comfort Crossover experiment Double-blind 18 normal, healthy employees working in one of two rooms, whereby room 1 had windows providing air ventilation and room 2 was mechanically ventilated 18
Misiaszek et al., 1987[14]a,b Evaluate effect of negative ions on manic behavior and sleep Experimental (phase I: no control group; phase II: with-in subjects, repeated measures) Phase I: No Blinding Phase II: Double-blind 8 manic patients (age range: 22–49) Phase I: 4 Phase II: 4
Reilly and Stevenson, 1993[33]a Evaluate effect of negative ions on anxiety Crossover experiment Single-blind (subjects) 8 healthy men (age range: 19–25) 8
Terman and Terman, 1995[6]d Evaluate effect of negative ions on seasonal depression Randomized controlled trial Double-blind 25 patients (mean age: 38.2 ± 11) with winter depression Low-density negative ion group: 13 High-density negative ion group: 12
Watanabe et al., 1997[35]a,c Evaluate effect of negative ions on mood and pleasantness Crossover experiment Single-blind (subjects) 13 healthy adults (age range: 21–49; mean age: 26.4) 13
Terman et al., 1998[8]b,d Evaluate effect of negative ions on sleep and seasonal depression Crossover experiment Double-blind 124 subjects (age range: 18–59; mean age: 39.4 ± 9.8) with seasonal affective disorder 124 (20 randomized to high-density negative ionization and 19 randomized to low-density negative ionization)
Nakane et al., 2002[10]a Evaluate effect of negative ions on anxiety Crossover experiment Not reported 12 female undergraduates (age range: 18–22) 12
Iwama et al., 2004[39]b Evaluate effect of negative ions on tension Randomized controlled trial Double-blind 44 patients randomized to the control and 51 patients randomized to receive treatment (mean age among men: 37 ± 18; mean age among women: 43 ± 20) 95
Goel et al., 2005[22]b,d Evaluate effect of negative ions on sleep and chronic depression Randomized controlled trial Double-blind 32 patients (age range: 22–65; mean age: 43.7 ± 12.4) with non-seasonal chronic depression 32 (22 randomized to low- or high-density)
Goel and Etwaroo, 2006[5]a,b,d Evaluate effect of negative ions on depression, total mood disturbance, and anger Randomized controlled trial Single-blind (subjects) 118 mildly depressed and non-depressed college students (mean age: 19.4 ± 1.7) 118 (59 randomized to low or high density)
Terman and Terman, 2006[7]b,d Evaluate effect of negative ions on sleep and seasonal depression Randomized controlled trial Double-blind 99 adults with seasonal depression (94 cases) and bipolar II disorder (five cases) (age range: 19–63; mean age: 40.4 ± 10.4) 99 (39 randomized to low or high density)
Gianinni et al., 2007[26]a Evaluate effect of negative ions on manic states Crossover experiment Double-blind 24 manic male patients (age range: 23–29; mean age: 26.7) 24 (20 analyzed)
Malcolm et al., 2009[32]a,b Evaluate effect of negative ions on positive affective memory Randomized controlled trial Single-blind (subjects) 30 healthy subjects (age range: 18–28) randomized to either receive high-density negative air ion exposure or to a control condition 30
Flory et al., 2010[4]d Evaluate effect of negative ions on seasonal depression Randomized controlled trial Single-blind (subjects) 73 university-affiliated women (age range: 18–51; mean age: 20.8 ± 5.69) with seasonal affective disorder 73 (38 randomized to low or high density)
Malik et al., 2010[9]a Evaluate effect of negative ions on psychological stress Crossover experiment Single-blind (subjects) 20 regular users of computers as part of their job (age range: 24–35; mean age: 28.9) 20
Dauphinais et al., 2012[24]d Evaluate the effect of negative air ions on seasonal depression Randomized controlled trial Double-blind 44 adult patients (20 in the low-density group) with bipolar depression 20
Harmer et al., 2012[31]a,b,d Evaluate the effect of high-density negative air ions on emotional processing in patients with seasonal depression Randomized controlled trial Double-blind 21 adult patients with seasonal depression; 21 controls. Mean ages of groups between 30–35 years 42
  1. aActivation, anxiety, mood.
  2. bRelaxation and sleep.
  3. cPersonal comfort rating.
  4. dDepression.